DEFINITION Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. Chemically, fats are generally triesters of glycerol and fatty acids. Fats may be either solid or liquid at normal room temperature, depending on their structure and composition. Although the words "oils", "fats", and "lipids" are all used to refer to fats, "oils" is usually used to refer to fats that are liquids at normal room temperature, while "fats" is usually used to refer to fats that are solids at normal room temperature. "Lipids" is used to refer to both liquid and solid fats, along with other related substances. The word "oil" is used for any substance that does not mix with water and has a greasy feel, such as petroleum (or crude oil) and heating oil, regardless of its chemical structure.[1]

Fats form a category of lipid, distinguished from other lipids by their chemical structure and physical properties. This category of molecules is important for many forms of life, serving both structural and metabolic functions. They are an important part of the diet of most heterotrophs (including humans). Fats or lipids are broken down in the body by enzymes called lipases produced in the pancreas.

Examples of edible animal fats are lard (pig fat), fish oil, and butter or ghee. They are obtained from fats in the milk, meat and under the skin of the animal. Examples of edible plant fats are peanut, soya bean, sunflower, sesame, coconut, olive, and vegetable oils. Margarine and vegetable shortening, which can be derived from the above oils, are used mainly for baking. These examples of fats can be categorized into saturated fats and unsaturated fats.

CLASSIFICATION Saturated fat is fat that consists of triglycerides containing only saturated fatty acids. There are several kinds of naturally occurring saturated fatty acids, which differ by the number of carbon atoms - from 1 to 24. Saturated fatty acids have no double bonds between the carbon atoms of the fatty acid chain and are thus fully saturated with hydrogen atoms.

Fat that occurs naturally in living matter contains varying proportions of saturated and unsaturated fat. Examples of foods containing a high proportion of saturated fat include dairy products (especially cream and cheese but also butter and ghee), animal fats such as suet, tallow, lard and fatty meat, coconut oil, cottonseed oil, palm kernel oil, chocolate, and some prepared foods[1].

TYPES OF SATURATED FATS Butyric acid (from Greek βούτυρος = butter), also known under the systematic name butanoic acid, is a carboxylic acid with the structural formula C H 3CH2CH2-COOH. It is found in rancid butter, parmesan cheese, vomit, and body odor and has an unpleasant smell and acrid taste, with a sweetish aftertaste (similar to ether). Butyric acid can be detected by mammals with good scent detection abilities (such as dogs) at 10 ppb, whereas humans can detect it in concentrations above 10 ppm.

USE OF BUTYRIC ACID Uses

Butyric acid is used in the preparation of various butanoate esters. Low-molecular-weight esters of butyric acid, such as methyl butanoate, have mostly pleasant aromas or tastes. As a consequence, they find use as food and perfume additives. They are also used in organic laboratory courses, to teach the Fischer esterification reaction.

TYPES OF SATURATED FAT Caprylic acid is the common name for the eight-carbon saturated fatty acid known by the systematic name octanoic acid. It is found naturally in coconuts and breast milk. It is an oily liquid that is minimally soluble in water with a slightly unpleasant rancid-like smell.

Uses

Caprylic acid is used commercially in the production of esters used in perfumery and also in the manufacture of dyes.

Caprylic acid is known to have anti-fungal properties, and is often recommended by nutritionists for the treatment of candidiasis. Caprylic acid is excellent for dealing with candida in the intestines which can occur frequently.[citation needed]

Caprylic acid is also used in the treatment of some bacterial infections. Due to its relatively short chain length it has no difficulty in penetrating fatty cell wall membranes, hence its effectiveness in combating certain lipid-coated bacteria, such as Staphylococcus aureus and various species of Streptococcus. [2]

Caprylic acid, aka, octanoic acid, must be covalently linked to the serine residue at the 3-position of ghrelin, specifically, it must acylate the -OH group, for ghrelin to have its hunger-stimulating action on the feeding centers of the hypothalamus, though other fatty acids may have similar effects.

TYPES OF SATURATED FATS Decanoic acid, or capric acid, is a saturated fatty acid. Its formula is CH3(CH2)8COOH. Salts and esters of decanoic acid are called decanoates.

USE It is used in organic synthesis and industrially in the manufacture of perfumes, lubricants, greases, rubber, dyes, plastics, food additives and pharmaceuticals.

TYPES OF SATURATED FATS Lauric acid (systematically: dodecanoic acid), a saturated fatty acid, is a white, powdery solid with a faint odor of bay oil or soap.

Uses

Lauric acid is inexpensive, has a long shelf-life, and is non-toxic and safe to handle. Thus, it is often used in laboratory investigations of melting point depression. Lauric acid

is a solid at room temperature but melts easily in boiling water, so liquid lauric acid can be treated with various solutes and used to determine their molecular masses.[citation needed]

TYPES OF SATURATED FAT Myristic acid, also called tetradecanoic acid or 14:0 is a common saturated fatty acid with the molecular formula CH3(CH2)12COOH. A myristate is a salt or ester of myristic acid.

Myristic acid is named after the Nutmeg Myristica fragrans. Nutmeg butter is 75% trimyristin, the triglyceride of myristic acid. Besides nutmeg, myristic acid is also found in palm oil, coconut oil, butter fat and spermacetin, the crystallized fraction of oil from the sperm whale.

Myristic acid is also commonly added co-translationally to the penultimate, nitrogen terminus, glycine in receptor-associated kinases to confer the membrane localisation of the enzyme. The myristic acid has a sufficiently high hydrophobicity to become incorporated into the fatty acyl core of the phospholipid bilayer of the plasma membrane of the eukaryotic cell. In this way, myristic acid acts as a lipid anchor in biomembranes.

The ester isopropyl myristate is used in cosmetic and topical medicinal preparations where good absorption through the skin is desired.

Reduction of myristic acid yields myristyl alcoho

TYPES OF SATURATED FATS Palmitic acid,CH3(CH2)14COOH or hexadecanoic acid in IUPAC nomenclature, is one of the most common saturated fatty acids found in animals and plants. As its name indicates, it is a major component of the oil from palm trees (palm oil and palm kernel oil). The word palmitic is from the French "palmitique", the pith of the palm tree. Palmitic acid was discovered by Edmond Frémy in 1840, in saponified palm oil.[3] Butter, cheese, milk and meat also contain this fatty acid. [4]

Palmitate is a term for the salts or esters of palmitic acid. The palmitate anion is the observed form of palmitic acid at physiological pH.[citation needed]

Uses

Retinyl palmitate is an antioxidant and a vitamin A compound added to low-fat milk to replace the vitamin content lost through the removal of milk fat. Palmitate is attached to the alcohol form of vitamin A, retinol, in order to make vitamin A stable in milk.[citation needed]

Derivatives of palmitic acid were used in combination with naphtha during World War II to produce napalm (aluminum naphthenate and aluminum palmitate). [6]

The World Health Organization claims there is convincing evidence that dietary intake of palmitic acid increases risk of developing cardiovascular diseases. [7] However, possibly less-disinterested studies have shown no ill effect, or even a favorable effect, of dietary consumption of palmitic acid on blood lipids and cardiovascular disease, so that the

WHO finding may be deemed controversial.[8] However, another study showed that palmitic acid has no hypercholesterolaemic effect if intake of linoleic acid is greater than 4.5% of energy. On the other hand, it was shown that, if the diet contains trans fatty acids, the health effects are negative, causing an LDL cholesterol increase and HDL cholesterol decrease. [9]

TYPES OF SATURATED FATS Stearic acid (first syllable rhymes with either bear or gear) (IUPAC systematic name: octadecanoic acid) or 18:0 is a saturated fatty acid. It is a waxy solid, and its chemical formula is C18H36O2. Its name comes from the Greek word stéar (genitive: stéatos), which means tallow. The salts and esters of stearic acid are called stearates.

Uses

Stearic acid is useful as an ingredient in making candles, plastics, dietary supplements, oil pastels and cosmetics, and for softening rubber.[2] It is used to harden soaps, particularly those made with vegetable oil.

Stearic acid is also used as a parting compound when making plaster castings from a plaster piece mold or waste mold and when making the mold from a shellacked clay original. In this use, powdered stearic acid is dissolved in water and the solution is brushed onto the surface to be parted after casting.

Esters of stearic acid with ethylene glycol, glycol stearate and glycol distearate, are used to produce a pearly effect in shampoos, soaps, and other cosmetic products. They are added to the product in molten form and allowed to crystalize under controlled conditions.

In fireworks, stearic acid is often used to coat metal powders such as aluminium and iron. This prevents

TYPES OF SATURATED FATS Arachidic acid, also called eicosanoic acid, is a saturated fatty acid found in peanut oil. Its name derives from the Latin arachis — peanut. It can be formed by the hydrogenation of arachidonic acid. It is practically insoluble in water, and stable under normal conditions. It is a surfactant.

Reduction of arachidic acid yields arachidyl alcohol.

MONOSATURATED FATS monounsaturated fats are fatty acids that have a single double bond in the fatty acid chain and all the carbon atoms in the chain are single-bonded. By contrast, polyunsaturated fatty acids have more than one double bond.

Fatty acids are long-chained molecules having a methyl group at one end and a carboxylic acid group at the other end. Fatty acid fluidity increases with increasing

number of double bonds. Therefore, monounsaturated fatty acids have a higher melting temperature than polyunsaturated fatty acids but lower than saturated fatty acids. Monounsaturated fatty acids are liquids at room temperature and semisolid or solid when refrigerated.

sources

Monounsaturated fats are found in natural foods such as nuts and avocados, and are the main component of tea seed oil and olive oil (oleic acid). Canola oil is 57%–60% monounsaturated fat, olive oil is about 75% monounsaturated fat while tea seed oil is commonly over 80% monounsaturated fat. Other sources include grapeseed oil, ground nut oil, peanut oil, flaxseed oil, sesame oil, corn oil, popcorn, whole grain wheat, cereal, oatmeal, safflower oil, sunflower oil, tea-oil Camellia, avocado oil.

TYPES OF MONOSATURATED FATS Oleic acid is a monounsaturated omega-9 fatty acid found in various animal and vegetable sources. It has the formula C18H34O2 (or CH3(CH2)7CH=CH(CH2)7COOH).[2] The saturated form of this acid is stearic acid.

Uses

Oleic acid may hinder the progression of ALD, or Adrenoleukodystrophy, a fatal disease that affects the brain and adrenal glands.[8]

Oleic acid is also the most abundant fatty acid in human adipose tissue.[citation needed]

TYPES OF MONOSATURATED FATS Erucic acid is a monounsaturated omega-9 fatty acid, denoted 22:1 ω-9. It is prevalent in rapeseed, wallflower seed, and mustard seed, making up 40-50% of their oils. Erucic acid is also known as cis-13-docosenoic acid and the trans isomer is known as brassidic acid.

Uses

It has many of the same uses as mineral oils but with the advantage that it is more readily bio-degradable. Its high tolerance to temperature makes it suitable for transmission oil. Its ability to polymerize and dry means it can be - and is - used as a binder for oil paints. Erucic acid will readily form many organic compounds. Adding this ability to its polymerizing characteristics makes it very suitable for use as organic matrices that need to be polymeric. This makes it especially useful in the manufacture of emulsions to coat photographic films and papers. A complex cocktail of many different erucic acid compounds is commonly used in just one roll of color film. It is widely used to produce emollients, especially for skin and healthcare products. Like other fatty acids, it gets converted into surfactants. Erucic acid is especially valued in tribology as a superior lubricant. When used in the manufacture of plastic films in the form of erucamide, it migrates to the surfaces and so resists the sticking of each film to its neighbor. Being a hydrocarbon of high calorific value, with a very low flash point, high

cetane rating, and good lubrication qualities, erucic acid can be a valuable component of bio-diesel. When converted into behenyl alcohol (CH3(CH2)21OH), erucic acid has many further uses such as a pour point depressant, enabling liquids to flow at a lower temperature and silver behenate for use in photography.[1]

TYPES OF MONOSATURATED FATS Nervonic acid is a monounsaturated omega-9 fatty acid. Nervonic acid has been identified as important in the biosynthesis of nerve cell myelin.[2] It is found in the sphingolipids of white matter in human brain.

Nervonic acid is used in the treatment of disorders involving demyelination, such as adrenoleukodystrophy and multiple sclerosis where there is a decreased level of nervonic acid in sphingolipids.[3]

POLYUNSATURATED FAT

polyunsaturated fat is an abbreviation of polyunsaturated fatty acid. That is a fatty acid in which more than one double bond exists within the representative molecule. That is, the molecule has two or more points on its structure capable of supporting hydrogen atoms not currently part of the structure. Polyunsaturated fatty acids can assume a cis or trans conformation depending on the geometry of the double bond.

The lack of the extra hydrogen atoms on the molecule's surface typically reduces the strength of the compound's intermolecular forces, thus causing the melting point of the compound to be significantly lower. This property can be observed by comparing predominately unsaturated vegetable oils, which remain liquid even at relatively low temperatures, to much more saturated fats such as butter or lard which are mainly solid at room temperature. Trans fats are more similar to saturated fat than are cis fats in many respects, including the fact that they solidify at a lower temperature.

Chemical structure of the polyunsaturated fat linoleic acid.

3D representation of linoleic acid in a bent conformation.

A fatty acid has a carboxylic acid at one end and a methyl group at the other end. Carbon atoms in a fatty acid are identified by Greek letters on the basis of their distance from the carboxylic acid. The carbon atom closest to the carboxylic acid is the alpha carbon, the next adjacent carbon is the beta carbon, etc. In a long-chain fatty acid the carbon atom in the methyl group is called the omega carbon because omega is the last letter of the Greek alphabet.

Omega-3 fatty acids have a double bond three carbons away from the methyl carbon, whereas omega-6 fatty acids have a double bond six carbons away from the methyl carbon. The illustration below shows the omega-6 fatty acid, linoleic acid.

TYPES OF POLYUNSATURATED FAT

Linoleic acid (LA) is an unsaturated omega-6 fatty acid. It is a colorless liquid. In physiological literature, it is called 18:2(n-6). Chemically, linoleic acid is a carboxylic acid with an 18-carbon chain and two cis double bonds; the first double bond is located at the sixth carbon from the omega end.

The word linoleic comes from the Greek word linon (flax). Oleic means of, relating to, or derived from oil or of or relating to oleic acid since removing the omega-6 double bond produces oleic acid.

USES

Linoleic acid is a polyunsaturated fatty acid used in the biosynthesis of prostaglandins. It is found in the lipids of cell membranes. It is abundant in many vegetable oils, especially safflower and sunflower oils.

To be fully utilised by the body, LA must be converted into gamma-linolenic acid, a reaction catalysed by the enzyme delta-6-desaturase (D6D).

Linoleic acid is a member of the group of essential fatty acids called omega-6 fatty acids, so called because they are an essential dietary requirement for all mammals. The other group of essential fatty acids is the omega-3 fatty acids, for example Alpha-linolenic acid. Omega-6 deficiency symptoms include dry hair, hair loss,[2] and poor wound healing.[3] It is easy to meet the daily requirement for these fatty acids (even for people consuming low fat diets) and most people get plenty of omega-6 fatty acids in their diet by consuming approximately a tablespoon of polyunsaturated plant oils per day.[citation needed]

A high consumption of omega-6 polyunsaturated fatty acids (PUFAs), which are found in most types of vegetable oil [e.g. corn oil - the most consumed oil in USA], may indeed increase the likelihood that postmenopausal women will develop breast cancer [4] .

Similar effect was observed on prostate cancer [5] . The analysis suggested an inverse association between total polyunsaturated fatty acids [omega-6] and breast cancer risk, but individual polyunsaturated fatty acids behaved differently [from each other]. [...] a derivative of linoleic acid [...] was inversely associated with the risk of breast cancer[6]

Industrial uses

Linoleic acid is used in making soaps, emulsifiers, and quick-drying oils. Reduction of linoleic acid yields linoleyl alcohol. Linoleic acid has become increasingly popular in the beauty products industry because of its beneficial properties on the skin. Research points to linoleic acid's effective properties when applied topically on the skin, ie. anti-inflammatory, acne reduction, moisture retention properties.[7][8][9] Noni seed oil is abundant in linoleic acid, and a number of beauty products contain noni seed oil.[citation

needed]

Foods

Oils and foods that contain linoleic acid include corn oil (59 %),cottonseed oil (49-58%), soybean oil (51%), safflower oil (78%), poppy seed oil (70%), hemp oil (50-70%), canola oil (21%), walnut oil (51%), grain-fed cow milk, olive oil (10%), palm oil (10%), sunflower oil (68%), lard (10%), egg yolks (16%), spirulina, peanut oil (48%), okra, rice bran oil (39%), wheat germ oil (55%), grape seed oil (73%), macadamia oil (1-3%), pistachio oil (32.7%), sesame oil (45%),cocoa butter (3%),coconut oil (2%), butter (2%).

TYPES OF POLYUNSATURATED FAT

Linolenic acid can refer to either of two fatty acids:

Alpha-linolenic acid – an ω-3 fatty acid found in many vegetable oils. The unmodified term linolenic acid most commonly refers to this substance.

Gamma-linolenic acid – an ω-6 fatty acid

α -Linolenic acid is an organic compound found in many common vegetable oils. Systematically, it is named all-cis-9,12,15-octadecatrienoic acid.[1] In physiological literature, it is given the name 18:3 (n−3).

α-linolenic acid is a carboxylic acid with an 18-carbon chain and three cis double bonds. The first double bond is located at the third carbon from the n end. Thus, α-linolenic acid is a polyunsaturated n −3 (omega-3) fatty acid. It is an isomer of γ-linolenic acid, a polyunsaturated n −6 (omega-6) fatty acid.

γ-Linolenic acid (gamma-linolenic acid or GLA, sometimes called gamoleic acid) is an essential fatty acid found primarily in vegetable oils. It is sold as a dietary supplement for treating problems with inflammation and auto-immune diseases. The efficacy of such use is disputed.

TYPES OF POLYUNSATURATED FAT Eicosapentaenoic acid (EPA or also icosapentaenoic acid) is an omega-3 fatty acid. In physiological literature, it is given the name 20:5(n-3). It also has the trivial name timnodonic acid. In chemical structure, EPA is a carboxylic acid with a 20-carbon chain and five cis double bonds; the first double bond is located at the third carbon from the omega end.

EPA and its metabolites act in the body largely by their interactions with the metabolites of arachidonic acid; see Essential fatty acid interactions for detail.

EPA is a polyunsaturated fatty acid that acts as a precursor for prostaglandin-3 (which inhibits platelet aggregation), thromboxane-3, and leukotriene-5 groups (all eicosanoids).

Sources

It is obtained in the human diet by eating oily fish or fish oil—cod liver, herring, mackerel, salmon, menhaden and sardine. It is also found in human breast milk and in snake oil.

However, fish do not naturally produce EPA, but obtain it from the algae they consume.[1] It is available to humans from some non-animal sources (eg, commercially, from spirulina and microalgae). Microalgae are being developed as a commercial source.[2] EPA is not usually found in higher plants, but it has been reported in trace amounts in purslane.[3] Microalgae, and supplements derived from it, are excellent alternative sources of EPA and other fatty acids, since fish often contain toxins due to pollution.[1]

The human body can (and in case of a purely vegetarian diet often must, unless the aforementioned algae or supplements derived from them are consumed) also convert α-linolenic acid (ALA) to EPA, but this is much less efficient than the resorption of EPA from food containing it, and ALA is itself an essential fatty acid, an appropriate supply of which must be ensured. Because EPA is also a precursor to docosahexaenoic acid (DHA), ensuring a sufficient level of EPA on a diet containing neither EPA nor DHA is harder both because of the extra metabolic work required to synthesize EPA and because of the use of EPA to metabolize DHA. Medical conditions like diabetes or certain allergies may significantly limit the human body's capacity for metabolization of EPA from ALA.[4]

Clinical significance(USES)

The US National Institute of Health's MedlinePlus lists a large number of conditions in which EPA (alone or in concert with other ω-3 sources) is known or thought to be effective.[5] Most of these involve its ability to lower inflammation.

Among omega-3 fatty acids, in particular EPA is thought to possess beneficial potential in mental conditions, such as schizophrenia.[6][7] Several studies report an additional

reduction in scores on symptom scales used to assess the severity of symptoms, when additional EPA is taken.

Recent studies have suggested that EPA may affect depression, and importantly, suicidal behavior. One such study,[8] took blood samples of 100 suicide-attempt patients and compared the blood samples to those of controls and found that levels of Eicosapentaenoic acid were significantly lower in the washed red blood cells of the suicide-attempt patients.

EPA has inhibitory effect on CYP2C9 and CYP2C19 hepatic enzymes. At high dose, it may also inhibit the activity of CYP2D6 and CYP3A4, important enzymes involved in drug metabolism.[9]

TYPES OF POLYUNSATURATDE FAT Dipicolinic acid (pyridine-2,6-dicarboxylic acid) is a chemical compound which composes 5% to 15% of the dry weight of bacterial spores.[2][3] It is implicated as responsible for the heat resistance of the endospore.[4][2]

However, mutants resistant to heat but lacking dipicolinic acid have been isolated, suggesting other mechanisms contributing to heat resistance are at work.[5]

Two genera of bacteria are known to produce endospores: the aerobic Bacillus and anaerobic Clostridium.[6]

TYPES OF POLYUNSATURATED FAT Docosahexaenoic acid (commonly known as DHA; 22:6(ω-3), all-cis-docosa-4,7,10,13,16,19-hexa-enoic acid; trivial name cervonic acid) is an omega-3 essential fatty acid. In chemical structure, DHA is a carboxylic acid with a 22-carbon chain [1] and six cis double bonds; the first double bond is located at the third carbon from the omega end.[2]

Fish oils are rich in DHA. Most of the DHA in fish and more complex organisms originates in photosynthetic and heterotrophic microalgae, and becomes increasingly concentrated in organisms as it moves up the food chain. DHA is also commercially manufactured from microalgae; Crypthecodinium cohnii and another of the genus Schizochytrium.[3] DHA manufactured using microalgae is vegetarian .[3] Most animals make very little DHA through metabolism; however small amounts are manufactured internally through the consumption of α-linolenic acid, an omega-3 fatty acid found in plants, animals, and milk.

DHA is metabolized to form the docosanoids—several families of potent hormones. DHA is a major fatty acid in sperm and brain phospholipids, and especially in the retina. Dietary DHA may reduce the risk of heart disease by reducing the level of blood triglycerides in humans. Low levels of DHA result in reduction of brain serotonin levels[4] and have been associated with ADHD, Alzheimer's disease, and depression, among other diseases, and there is mounting evidence that DHA supplementation may be effective in combating such diseases (see external links at the end of this article).

Health

Alzheimer's Disease

A large NIH drug trial is currently recruiting patients for evaluating DHA in Alzheimer's disease.[14] This is the first human trial of DHA. Animal studies in the TG3 transgenic mouse model of Alzheimer's disease linked decreases in amyloid plaques and tau to dietary DHA. Animal studies also show that when combined with arachidonic acid (also present in fish oil), the effectiveness of DHA for preventing plaques was less than without it.

Cancer

DHA was found to inhibit growth of human colon carcinoma cells[15][16], more than other omega-3 PUFAs. The cytotoxic effect of DHA wasn't caused by increased lipid peroxidation or any other oxidative damage, but rather decrease in cell growth regulators. However, different cancer lines handle PUFAs differently and display different sensitivities towards them. Martek Biosciences Corporation, which provided DHA for one of these studies, sponsors research of DHA benefits. Steve Dubin, CEO of Martek reportedly said "We want to be the 'Intel inside' with DHA - we need to get across that the real benefit is there"[17].

Pregnancy and lactation

DHA concentrations in breast milk range from 0.07% to greater than 1.0% of total fatty acids, with a mean of about 0.34%. DHA levels in breast milk are higher if a mother's diet is high in fish.

DHA has recently gained attention as a supplement for pregnant women,[18] noting studies of improved attention and visual acuity. One recent study indicates that low levels of plasma and erythrocyte DHA were associated with poor retinal development, low visual acuity, and poor cognitive development. In that same study, alpha-linolenic acid was shown as a source of fetal DHA, but that performed DHA was more readily accredited. A working group from the ISSFAL (International Society for the Study of Fatty Acids and Lipids) recommended 300 mg/day of DHA for pregnant and lactating women, whereas the average consumption was between 45 mg and 115 mg per day of the women in the study. Other requirements are available from other sources.[19]

DHA has been an ingredient in several brands of premium infant formula sold in North America since 2001 after Mead Johnson, the first infant formula manufacturer to add DHA and ARA (arachidonic acid) to its Enfamil Lipil product, received approval by the Food and Drug Administration and Health Canada. Both DHA and ARA, manufactured by Martek Biosciences Corporation, are permitted in infant formula. The addition of DHA at dose-effective levels has been shown to improve cognitive function in both term and preterm infants.

DHA makes infant formulas more like human milk than "conventional" formula containing Alpha-linolenic acid and linoleic acid, which are precursors to DHA. Formula sold in North America uses lipids from microorganisms grown in bioreactors as sources of DHA.[20][3]

OTHER TYPES OF FATS

n−3 fatty acids (popularly referred to as ω−3 fatty acids or omega-3 fatty acids) are a family of unsaturated fatty acids that have in common a final carbon–carbon double bond in the n −3 position; that is, the third bond from the methyl end of the fatty acid.

Important nutritionally essential n−3 fatty acids are: α-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), all of which are polyunsaturated. The human body cannot synthesize n−3 fatty acids de novo, but it can form 20- and 22-carbon unsaturated n−3 fatty acids from the eighteen-carbon n−3 fatty acid, α-linolenic acid. These conversions occur competitively with n−6 fatty acids, which are essential closely related chemical analogues that are derived from linoleic acid. Both the n−3 α-linolenic acid and n−6 linoleic acid are essential nutrients which must be obtained from food. Synthesis of the longer n−3 fatty acids from linolenic acid within the body is competitively slowed by the n−6 analogues. Thus accumulation of long-chain n−3 fatty acids in tissues is more effective when they are obtained directly from food or when competing amounts of n−6 analogs do not greatly exceed the amounts of n−3.

Chemistry

The term n−3 (also called ω−3 or omega-3) signifies that the first double bond exists as the third carbon-carbon bond from the terminal methyl end (n) of the carbon chain.

n−3 fatty acids which are important in human nutrition are: α-linolenic acid (18:3, n−3; ALA), eicosapentaenoic acid (20:5, n−3; EPA), and docosahexaenoic acid (22:6, n−3; DHA). These three polyunsaturates have either 3, 5 or 6 double bonds in a carbon chain of 18, 20 or 22 carbon atoms, respectively. All double bonds are in the cis-configuration, i.e. the two hydrogen atoms are on the same side of the double bond.

Most naturally-produced fatty acids (created or transformed in animalia or plant cells with an even number of carbon in chains) are in cis-configuration where they are more easily transformable. The trans-configuration results in much more stable chains that are very difficult to further break or transform, forming longer chains that aggregate in tissues and lacking the necessary hydrophilic properties. This trans-configuration can be the result of the transformation in alkaline solutions, or of the action of some bacterias that are shortening the carbonic chains. Natural transforms in vegetal or animal cells more rarely affect the last n−3 group itself. However, n−3 compounds are still more fragile than n−6 because the last double bond is geometrically and electrically more exposed, notably in the natural cis configuration.

OTHER TYPES OF FAT n−6 fatty acids (popularly referred to as ω−6 fatty acids or omega-6 fatty acids) are a family of unsaturated fatty acids which have in common a final carbon–carbon double bond in the n −6 position; that is, the sixth bond from the end of the fatty acid.

The biological effects of the n−6 fatty acids are largely mediated by their conversion to n-6 eicosanoids that bind to diverse receptors found in every tissue of the body. The conversion of tissue arachidonic acid (20:4n-6) to n-6 prostaglandin and n-6 leukotriene hormones provides many targets for pharmaceutical drug development and treatment to diminish excessive n-6 actions in atherosclerosis, asthma, arthritis, vascular disease, thrombosis, immune-inflammatory processes and tumor proliferation. Competitive interactions with the n −3 fatty acids affect the relative storage, mobilization, conversion and action of the n-3 and n-6 eicosanoid precursors. (See Essential fatty acid interactions for more information.)

Negative health effects

Some medical research suggests that excessive levels of n−6 fatty acids, relative to n−3 fatty acids, may increase the probability of a number of diseases and depression.[1][2][3]

Modern Western diets typically have ratios of n−6 to n−3 in excess of 10 to 1, some as high as 30 to 1. The optimal ratio is thought to be 4 to 1 or lower.[4][5]

Excess n−6 fats interfere with the health benefits of n−3 fats; in part because they compete for the same rate-limiting enzymes. A high proportion of n−6 to n−3 fat in the diet shifts the physiological state in the tissues toward the pathogenesis of many diseases: prothrombotic, proinflammatory and proconstrictive.[6]

Chronic excessive production of n−6 eicosanoids is associated with heart attacks, thrombotic stroke, arrhythmia, arthritis, osteoporosis, inflammation, mood disorders and cancer.[7] Many of the medications used to treat and manage these conditions work by blocking the effects of the potent n−6 fat, arachidonic acid.[8] Many steps in formation and action of n-6 hormones from n-6 arachidonic acid proceed more vigorously than the corresponding competitive steps in formation and action of n-3 hormones from n-3 eicosapentaenoic acid. [9] The COX-1 and COX-2 inhibitor medications, used to treat inflammation and pain, work by preventing the COX enzymes from turning arachidonic acid into inflammatory compounds.[10] (See Cyclooxygenase for more information.) The LOX inhibitor medications often used to treat asthma, work by preventing the LOX enzyme from converting arachidonic acid into the leukotrienes.[11][12] Many of the anti-mania medications used to treat bipolar disorder work by targeting the arachidonic acid cascade in the brain.[13]

A high consumption of omega-6 polyunsaturated fatty acids (PUFAs), which are found in most types of vegetable oil, may increase the likelihood that postmenopausal women will develop breast cancer [14] . Similar effect was observed on prostate cancer [15] . Other analysis suggested an inverse association between total polyunsaturated fatty acids

and breast cancer risk, but individual polyunsaturated fatty acids behaved differently [from each other]. [...] a 20:2 derivative of linoleic acid [...] was inversely associated with the risk of breast cancer[16].

OTHER TYPES OF FAT Trans fat is the common name for a type of unsaturated fat with trans-isomer fatty acid(s). Trans fats may be monounsaturated or polyunsaturated.

Unsaturated fat is a fat molecule containing one or more double bonds between the carbon atoms. Since the carbons are double-bonded to each other, there are fewer bonds available for hydrogen, so there are fewer hydrogen atoms, hence "unsaturated". Cis and trans are terms that refer to the arrangement of chains of carbon atoms across the double bond. In the cis arrangement, the chains are on the same side of the double bond, resulting in a kinked geometry. In the trans arrangement, the chains are on opposite sides of the double bond, and the chain is straight overall.

The process of hydrogenation is intended to add hydrogen atoms to cis-unsaturated fats, eliminating a double bond and making them more saturated. These saturated fats have a higher melting point, which makes them attractive for baking and extends their shelf-life. However, the process frequently has a side effect that turns some cis-isomers into trans-unsaturated fats instead of hydrogenating them completely.

There is another class of trans fats, vaccenic acid, which occurs naturally in trace amounts in meat and dairy products from ruminants.

Unlike other dietary fats, trans fats are neither essential nor salubrious [1] . The consumption of trans fats increases one's risk of coronary heart disease [2] by raising levels of "bad" LDL cholesterol and lowering levels of "good" HDL cholesterol.[3] Health authorities worldwide recommend that consumption of trans fat be reduced to trace amounts. Trans fats from partially hydrogenated oils are more deleterious than naturally occurring oils.[4]

Chemically, trans fats are made of the same building blocks as non-trans fats, but have a different arrangement. In trans fatty acid molecules, the hydrogen atoms are bonded to pairs of doubly bonded carbon atoms (characteristic of all unsaturated fats) in the trans rather than the cis arrangement. This results in a straight, rather than kinked, shape for the carbon chain, more like the straight chain of a fully saturated fat.

Health risks

Partially hydrogenated vegetable oils have been an increasingly significant part of the human diet for about 100 years (particularly so in the latter half of the 20th century), and some deleterious effects of trans fat consumption are scientifically accepted, forming the basis of the health guidelines discussed above.

The exact biochemical methods by which trans fats produce specific health problems are a topic of continuing research. The most prevalent theory is that the human lipase enzyme is specific to the cis configuration. A lipase is a water-soluble enzyme that catalyzes the hydrolysis of ester bonds in water-insoluble, lipid substrates. Lipases thus comprise a subclass of the esterases. Lipases perform essential roles in the digestion, transport and processing of dietary lipids (e.g. triglycerides, fats, oils) in most – if not all – living organisms. The human lipase enzyme is ineffective with the trans configuration, so trans fat remains in the blood stream for a much longer period of time and is more prone to arterial deposition and subsequent plaque formation. While the mechanisms through which trans fats contribute to coronary heart disease are fairly well understood, the mechanism for trans fat's effect on diabetes is still under investigation.

[edit] Coronary heart disease

The primary health risk identified for trans fat consumption is an elevated risk of coronary heart disease (CHD).[36] A comprehensive review of studies of trans fats was published in 2006 in the New England Journal of Medicine reports a strong and reliable connection between trans fat consumption and CHD, concluding that "On a per-calorie basis, trans fats appear to increase the risk of CHD more than any other macronutrient, conferring a substantially increased risk at low levels of consumption (1 to 3 percent of total energy intake)".[4] This study estimates that between 30,000 and 100,000 cardiac deaths per year in the United States are attributable to the consumption of trans fats.[37]

The major evidence for the effect of trans fat on CHD comes from the Nurses' Health Study (NHS) — a cohort study that has been following 120,000 female nurses since its inception in 1976. In this study, Hu and colleagues analyzed data from 900 coronary events from the NHS population during 14 years of followup. He determined that a nurse's CHD risk roughly doubled (relative risk of 1.94, CI: 1.43 to 2.61) for each 2% increase in trans fat calories consumed (instead of carbohydrate calories). By contrast, it takes more than a 15% increase in saturated fat calories (instead of carbohydrate calories) to produce a similar increase in risk. Eating non-trans unsaturated fats instead of carbohydrates reduces the risk of CHD rather than increasing it.[38][clarification needed] Hu also reports on the benefits of reducing trans fat consumption. Replacing 2% of food energy from trans fat with non-trans unsaturated fats more than halves the risk of CHD (53%). By comparison, replacing a larger 5% of food energy from saturated fat with non-trans unsaturated fats reduces the risk of CHD by 43%.[38]

Another study considered deaths due to CHD, with consumption of trans fats being linked to an increase in mortality, and consumption of polyunsaturated fats being linked to a decrease in mortality.[36][39]

There are two accepted tests that measure an individual's risk for coronary heart disease, both blood tests. The first considers ratios of two types of cholesterol, the other the amount of a cell-signalling cytokine called C-reactive protein. The ratio test is more accepted, while the cytokine test may be more powerful but is still being studied.[36] The effect of trans fat consumption has been documented on each as follows:

Cholesterol ratio: This ratio compares the levels of LDL (so-called "bad" cholesterol) to HDL (so-called "good" cholesterol). Trans fat behaves like saturated fat by raising the level of LDL, but unlike saturated fat it has the additional effect of decreasing levels of HDL. The net increase in LDL/HDL ratio with trans fat is approximately double that due to saturated fat.[40] (Higher ratios are worse.) One randomized crossover study published in 2003 comparing the postprandial effect on blood lipids of (relatively) cis and trans fat rich meals showed that cholesteryl ester transfer (CET) was 28% higher after the trans meal than after the cis meal and that lipoprotein concentrations were enriched in apolipoprotein(a) after the trans meals.[41]

C-reactive protein (CRP): A study of over 700 nurses showed that those in the highest quartile of trans fat consumption had blood levels of CRP that were 73% higher than those in the lowest quartile.[42]

[edit] Other effects

There are suggestions that the negative consequences of trans fat consumption go beyond the cardiovascular risk. In general, there is much less scientific consensus that eating trans fat specifically increases the risk of other chronic health problems:

Alzheimer's Disease : A study published in Archives of Neurology in February 2003 suggested that the intake of both trans fats and saturated fats promote the development of Alzheimer disease.[43]

Cancer : There is no scientific consensus that consumption of trans fats significantly increases cancer risks across the board.[36] The American Cancer Society states that a relationship between trans fats and cancer "has not been determined."[44] However, one recent study has found connections between trans fat and prostate cancer.[45] An increased intake of trans-fatty acids may raise the risk of breast cancer by 75 percent, suggest the results from the French part of the European Prospective Investigation into Cancer and Nutrition.[46][47]

Diabetes : There is a growing concern that the risk of type 2 diabetes increases with trans fat consumption.[36] However, consensus has not been reached.[4] For example, one study found that risk is higher for those in the highest quartile of trans fat consumption.[48] Another study has found no diabetes risk once other factors such as total fat intake and BMI were accounted for.[49]

Obesity : Research indicates that trans fat may increase weight gain and abdominal fat, despite a similar caloric intake.[50] A 6-year experiment revealed that monkeys fed a trans-fat diet gained 7.2% of their body weight, as compared to 1.8% for monkeys on a mono-unsaturated fat diet.[51] Although obesity is frequently linked to trans fat in the popular media,[52] this is generally in the context of eating too many calories; there is no scientific consensus connecting trans fat and obesity.

Liver Dysfunction : Trans fats are metabolized differently by the liver than other fats and interfere with delta 6 desaturase. Delta 6 desaturase is an enzyme involved in converting essential fatty acids to arachidonic acid and prostaglandins, both of which are important to the functioning of cells.[53]

Infertility : One 2007 study found, "Each 2% increase in the intake of energy from trans unsaturated fats, as opposed to that from carbohydrates, was associated with a 73% greater risk of ovulatory infertility…".[54]

OTHER TYPES OF FAT Cholesterol is a lipidic, waxy alcohol found in the cell membranes and transported in the blood plasma of all animals. It is an essential component of mammalian cell membranes where it is required to establish proper membrane permeability and fluidity. Cholesterol is the principal sterol synthesized by animals, but small quantities are synthesized in other eukaryotes, such as plants and fungi. It is almost completely absent among prokaryotes, which include bacteria.[2] Cholesterol is classified as a sterol (a contraction of ster oid and alcoh ol ).

Although cholesterol is essential for life, high levels in circulation are associated with atherosclerosis. Cholesterol is synthesized in virtually all cells, and significant amounts of it can be absorbed from the diet.

The name cholesterol originates from the Greek chole- (bile) and stereos (solid), and the chemical suffix -ol for an alcohol, as researchers first identified cholesterol in solid form in gallstones by François Poulletier de la Salle in 1769. However, it is only in 1815 that chemist Eugène Chevreul named the compound "cholesterine".[3]

FAT SUBSTITUES

Simplesse is a whey protein product used as a fat substitute in low-calorie foods. The manufacturer, CP Kelco (a former NutraSweet subsidiary), sells it to food processors as a "microparticulated whey protein concentrate" in dry powder form, and recommends that it be labelled as "dairy protein" on food labels. Its texture is due to its ability to form a colloid, similar to the way fat is dispersed in homogenized milk. It differs from other whey protein concentrate mainly by virtue of rheology; it is produced by a mechanical, rather than a chemical process.

Digestion and Absorption of Food Fats

Maintenance of a healthy digestive system requires input from lipids, which include molecules such as cholesterol, appropriate saturated and polyunsaturated fatty acids, and other lesser known components such as glycosphingolipids.

Cholesterol is the precursor to bile acids, which are needed to digest and absorb long-chain fatty acids. Cholesterol is also recognized for its physiological importance in the

skin and the intestine where it plays an important structural role as a component of the organ membranes.Cells lining the digestive tract are particularly rich in cholesterol.

Saturated fatty acids play their role in membrane integrity by providing appropriate fatty acids for certain parts of membrane structures. Among their various roles are the signaling activities that, for example, tell the gastrointestinal musculature when to contract. Polyunsaturated fatty acids also provide raw material for membranes, and work as precursors to the various prostaglandins, needed to maintain important functions of intestinal motility.

Glycosphingolipids are lipids with single sugar molecules attached found in cell membranes, especially in the brain. They also protect against gastrointestinal infections, especially in infants and children. Whole milk is an adequate source, especially human milk. Fat digestion of phospholipids and other lipids makes up very minor, but sometimes important, parts of the building blocks for tissues. These special lipids are usually made by the body and diet is not the major source.

Digestion of fatty acids from triglycerides is different for the regular long-chain fatty acids (14 carbons to 22 carbons) than it is for short- and medium-chain fatty acids (4 carbons to 12 carbons). Usually about 95 percent of the fat is available for digestion when the mixture of fatty acids is varied.

The digestion of regular fats and oils, which are usually long-chain triglycerides, requires bile acids as well as lipases. In adults this digestion usually starts in the small intestine and is done with the aid of lipases and bile acids. The bile acids allow the triglycerides to be properly emulsified and the lipases break the triglycerides into individual fatty acids and monoglycerides in the small intestine. When these parts are absorbed through the wall of the intestine, they are reassembled into triglycerides and carried into the body through the lymph system on chylomicrons.

Short- and medium-chain fatty acids from fats such as milk fat or coconut oil or palm kernel oil are broken off from the triglycerides without the need for bile acids. They are then shuttled directly to the liver through the portal artery without the use of chylomicrons. In the case of a meal with a large amount of lauric acid, some of this medium-chain fatty acid does travel via chylomicrons through the lymph system.

Fat digestion of cholesterol and other sterols is frequently not described accurately. Both cholesterol and other sterols do not provide any calories, and the amount that is absorbed is relatively small except in infants. Adults probably absorb only about 25 percent of the cholesterol they consume, and even less of the other sterols. Cholesterol plays a role in membrane structure as well as for production of bile acids and hormones. Other sterols are not usually part of the body’s tissues unless they are consumed in large amounts.

People ask why fat is digested more slowly than either protein or carbohydrate, and sometimes think that this means that there is a problem with digestion of fat; however,

the slow digestion is really only nature’s way of maintaining an even amount of the energy distribution.

Fat digestion in infants is somewhat different from fat digestion in adults, especially if the infants are fed human milk. The digestion of fats in the infant begins in the mouth with the function of several digestive enzymes that are special to the infant. The fatty acids are broken down in order to be well digested. A special enzyme coming from the mammary gland enables most of the cholesterol from the human milk to be absorbed by the infant. Cholesterol is a very important nutrient for the infant, especially for its role in brain and other central nervous system development. The typical infant formula is greatly lacking in cholesterol and also lacks the enzyme that aids in the absorption of cholesterol.

ADDITIONAL REFERENCES Alternative Names

Saturated fat; Diet - fat; Polyunsaturated fat; Monounsaturated fat; Lipids

Food Sources:

SATURATED FATS

These are the biggest dietary cause of high LDL levels ("bad cholesterol"). When looking at a food label, pay very close attention to the percentage of saturated fat and avoid or limit any foods that are high. Saturated fat should be limited to 10% of calories. Saturated fats are found in animal products such as butter, cheese, whole milk, ice cream, cream, and fatty meats. They are also found in some vegetable oils -- coconut, palm, and palm kernel oils. (Note: Most other vegetable oils contain unsaturated fat and are healthy.)

UNSATURATED FATS

Fats that help to lower blood cholesterol if used in place of saturated fats. However, unsaturated fats have a lot of calories, so you still need to limit them. Most (but not all!) liquid vegetable oils are unsaturated. (The exceptions include coconut, palm, and palm kernel oils.) There are two types of unsaturated fats:

Monounsaturated fats: Examples include olive and canola oils. Polyunsaturated fats: Examples include fish, safflower, sunflower, corn, and

soybean oils.

TRANS FATTY ACIDS

These fats form when vegetable oil hardens (a process called hydrogenation) and can raise LDL levels. They can also lower HDL levels ("good cholesterol"). Trans-fatty acids are found in fried foods, commercial baked goods (donuts, cookies, crackers), processed foods, and margarines.

HYDROGENATED AND PARTIALLY HYDROGENATED FATS

This refers to oils that have become hardened (such as hard butter and margarine). Partially hydrogenated means the oils are only partly hardened. Foods made with hydrogenated oils should be avoided because they contain high levels of trans fatty acids, which are linked to heart disease. (Look at the ingredients in the food label.)

EXCELLENT FOOD SOURCES

Saturated fats are found predominantly in animal products such as meat and dairy products, and are strongly associated with higher cholesterol levels. Tropical oils such as palm, coconut, and coconut butter, are also high in saturated fats.

Trans fatty acids are manufactured fats created during a process called hydrogenation, which is aimed at stabilizing polyunsaturated oils to prevent them from becoming rancid and to keep them solid at room temperature. They may be particularly dangerous for the heart and may pose a risk for certain cancers. Hydrogenated fats are used in stick margarine, fast foods, commercial baked goods (donuts, cookies, crackers), processed foods, and fried foods.

Calories are the basic unit of energy within food. When you eat, your body converts calories into energy and uses what it can and stores the rest in the form of fat. A calorie is a calorie, whether it comes from a brownie or a serving of raw broccoli. The difference between them is the number of calories, nutrients, fat, and other ingredients in a typical serving .

Omega-3 fatty acids are a form of polyunsaturated fat that the body derives from food. Omega-3s (and omega-6s) are known as essential fatty acids (EFAs) because they are important for good health. The body cannot make these fatty acids on its own so omega-3s must be obtained from food. These different types of acids can be obtained in foods such as cold-water fish including tuna, salmon, and mackerel. Other important omega 3 fatty acids are found in dark green leafy vegetables, flaxseed oils, and certain vegetable oils.

Omega-3 fatty acids have been found to be beneficial for the heart. Positive effects include anti-inflammatory and anti-blood clotting actions, lowering cholesterol and triglyceride levels, and reducing blood pressure. These fatty acids may also reduce the risks and symptoms for other disorders including diabetes, stroke, rheumatoid arthritis, asthma, inflammatory bowel disease, ulcerative colitis, some cancers, and mental decline.

DISEASES

Doctors know obese patients are at an increased risk of diabetes, cardiovascular disease and metabolic syndrome. But researchers now say the fat itself could be causing these diseases.

Fat biopsies from the upper thighs of lean and obese patients revealed to researchers that the fat tissues in obese patients were actually "sick" compared to the fat in lean patients. The obese fat samples themselves were more inflamed than lean fat samples and showed significant stress on the endoplasmic reticulum (ER) -- a component of all cells that helps synthesize proteins and monitor how they are folded.

When stressed, ER produces several proteins that ultimately lead to insulin resistance, which plays a major role in the development and progression of type 2 diabetes and metabolic syndrome.

Study authors say losing weight can help reduce stress on the ER, thus lowering the risk of insulin resistance and the resulting conditions. According to the National Institutes of Health, each time a body mass index (BMI) greater than 25 is raised by one point, the risk for diabetes increases 25 percent and the risk for heart disease increases 10 percen

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Recommended Dietary Allowances (RDA)

TOTAL FAT 765gSATURATED FATTY ACIDS

345g

CHOLESTEROL 3300mgSODIUM 2400mgPOTASSIUM 47000mgTOTAL CARBOHYDRATE

3000mg

FIBRE 205mgPROTEIN 500mg

History

The RDA was developed during World War II by Lydia J. Roberts, Hazel K. Stiebeling and Helen S. Mitchell, all part of a committee established by the U.S. National Academy of Sciences in order to investigate issues of nutrition that might "affect national defense" (Nestle, 35). The committee was renamed the Food and Nutrition Board in 1941, after which they began to deliberate on a set of recommendations of a standard daily allowance for each type of nutrient. The standards would be used for nutrition recommendations for the armed forces, for civilians, and for overseas population who

might need food relief. Roberts, Stiebeling, and Mitchell surveyed all available data, created a tentative set of allowances for "energy and eight nutrients", and submitted them to experts for review (Nestle, 35). The final set of guidelines, called RDAs for Recommended Dietary Allowances, were accepted in 1941. The allowances were meant to provide superior nutrition for civilians and military personnel, so they included a "margin of safety." Because of food rationing during the war, the food guides created by government agencies to direct citizens' nutritional intake also took food availability into account.

The Food and Nutrition Board subsequently revised the RDAs every five to ten years. In the early 1950s, USDA nutritionists made a new set of guidelines that also included the number of servings of each food group in order to make it easier for people to receive their RDAs of each nutrient.

In 1997 at the suggestion of the Institute of Medicine of the National Academy RDA became one part of a broader set of dietary guidelines called the Dietary Reference Intake used by both the United States and Canada.

ADDITIONAL REFERENCES

Fats

Lipids are organic substances consisting mostly of carbons and hydrogen atoms. They are hydrophobic, which means that they have little or no affinity to water. All lipids are soluble (or dissolvable) in nonpolar solvents, such as ether, alcohol, and gasoline. There are three families of lipids: (1) fats, (2) phospholipids, and (3) steroids.

Fatty acids and glycerol make up the larger molecule of fats. A fatty acid consists of a long carbon skeleton of 16 or 18 carbon atoms, though some are even longer. The carbonyl group, which is a carbon atom double-bonded to an oxygen atom and single-bonded to an oxygen attached to a hydrogen (OH-C=O), is the acidic group of the fatty acids. The acidic property is determined by the ability of the hydrogen to dissociate, or break away, from the oxygen atom. The carbonyl group is followed by a long chain of carbon atoms bonded to hydrogen, which is referred to as the hydrocarbon "tail." The long hydrocarbon tail gives fatty acids their hydrophobic, or "water-fearing" property. Fats cannot be dissolved in water because fats are nonpolar (an equal distribution of electrons) and water is polar (an unequal distribution of electrons). The polarity of water is unable to form bonds and break down the nonpolar fatty acid molecule.

There are different types of fatty acids, which vary in length and the number of bonds. Saturated fatty acids have single bonds between the carbon atoms that make up the tail. The carbon atoms are "full" or saturated, and therefore cannot take up any more hydrogen. Most animal fat, such as butter, milk, cheese, and coconut oil, are saturated. Unsaturated fatty acids have one or more double bonds between carbon atoms. A double bond is the sharing of four electrons between atoms, while a single bond is the

sharing of two electrons. The double bond has the ability to lend its extra two electrons to another atom, thereby forming another bond. Monounsaturated fatty acids contain only one double bond, such that each of the carbon atoms of the double bond can bond with a hydrogen atom. An example of monounsaturated fatty acids is oleic acid, which is found in olive oil. Polyunsaturated fatty acids contain two or more double bonds, such that four or more carbon atoms can bond with hydrogen atoms. Most vegetable fats are polyunsaturated fatty acids. The double bonds change the structure of the fatty acid, in that there is a slight bend where the double bond is located.

Foods high in saturated fatty acids include whole milk, cream, cheese, egg yolk, fatty meats (e.g., beef, lamb, pork, ham), coconut oil, regular margarine, and chocolate. Foods high in polyunsaturated fatty acids include vegetable oils (e.g., safflower, corn, cottonseed, soybean, sesame, sunflower), salad dressing made from vegetable oils, and fish such as salmon, tuna, and herring.

Triglycerides are the basic unit of fat and are composed of three ("tri-") fatty acids individually bonded to each of the three carbons of glycerol. Fatty acids rarely exist in a free form in nature because they are highly reactive, and therefore make bonds spontaneously.

Fat Function, Metabolism, and Storage

Fats and lipids play critical roles in the overall functioning of the body, such as in digestion and energy metabolism. Usually, 95 percent of the fat in food is digested and absorbed into adipose, or fatty, tissue. Fats are the body's energy provider and energy reserve, which helps the body maintain a constant temperature. Fats and lipids are also involved in the production and regulation of steroid hormones, which are hydrophobic (or "water-fearing") molecules made from cholesterol in the smooth endoplasmic reticulum, a compartment within a cell in which lipids, hormones, and proteins are made. Steroid hormones are essential in regulating sexuality, reproduction, and development of the human sex organs, as well as in regulating the water balance in the body. Steroid hormones can also freely flow in and out of cells, and they modify the transcription process, which is the first step in protein synthesis, where segments of the cell's DNA, or the genetic code, is copied.

Fats and lipids also have important structural roles in maintaining nerve impulse transmission, memory storage, and tissue structure. Lipids are the major component of cell membranes. The three most common lipids in the membranes of eukaryots, or nucleus-containing cells, are phospholipids, glycolipids, and cholesterol. A phospholipid has two parts: (1) the hydrophilic ("water-loving") head, which consists of choline, phosphate, and glycerol, and (2) the hydrophobic ("water-fearing") fatty acid tail, which consists of carbon and hydrogen. The hydrophilic head is the part of the phospholipids that is in contact with water, since it shares similar chemical properties with water molecules. The hydrophobic tail of the phospholipids faces inward, and therefore is able to avoid any contact with water. In this particular arrangement, the phospholipids arrange themselves in a bilayer (double layer) alignment in aqueous solution.

Fats are metabolized primarily in the small intestines because the enzymes of the stomach cannot break down fat molecules due to their hydrophobicity. In the small intestines, fat molecules stimulate the release of cholecystokinin (CCK), a small-intestine hormone, into the bloodstream. The CCK in the blood triggers the pancreas to release digestive enzymes that can break down lipids. The gallbladder is also stimulated to secrete bile into the small intestines. Bile acids coat the fat molecules, which results in the formation of small fat globules, which are called micelles. The coating prevents the small fat globules from fusing together to form larger fat molecules, and therefore the small fat globules are more easily absorbed. The pancreatic enzymes can also break down triglycerides into monoglycerides and fatty acids. Once this occurs, the broken-down fat molecules are able to diffuse into the intestinal cells, in which they are converted back to triglycerides, and finally into chylomicrons.

Chylomicrons, which are composed of fat and protein, are macromolecules that travel through the bloodstream into the lymphatic capillaries called lacteals. The lymphatic system is a special system of vessels that carries a clear fluid called lymph, in which lost fluid and proteins are returned to the blood. The lacteals absorb the fat molecules and transport them from the digestive tract to the circulatory system, dumping chylomicrons in the bloodstream. The adipose and liver tissues, which release enzymes called lipoprotein lipase, break down chylomicrons into monoglycerides and fatty acids. These molecules diffuse into the adipose and liver cells, where they are converted back to triglycerides and stored as the body's supply of energy.

Fat Nutrition

The energy value of fats is 9 kcal/gram (kilocalories per gram), which supplies the body with important sources of calories. Calories are units of energy. The breaking of bonds within fat molecules releases energy that the body uses. A kilocalorie is the unit used to measure the energy in foods. It is the equivalent of "calories" listed on Nutrition Facts labels on food packaging.

Some of the foods known to contain large amounts of fat include the obvious examples, such as butter on toast, fried foods, and hamburgers. But many of the foods that people consume on a daily basis have hidden sources of fat that may not be obvious to the person eating them. These foods include cookies and cakes, cheese, ice cream, potato chips, and hot dogs. One way to avoid foods that contain high amounts of fat is to look at the Nutrition Facts label located on the packages of most foods, where the total fat content of the food is listed.

Actual intake of fat can vary from 10 percent to 40 percent of the calories consumed daily, depending on personal or cultural regimens. Limiting one's daily fat intake to less than 30 percent of total calorie intake and increasing consumption of polyunsaturated fatty acids have been shown to be beneficial in maintaining a healthful diet.

Effects of Excess Dietary-Fat Intake

The recommended intake of fats in the American diet is to limit fats to below 30 percent of the total daily caloric intake. One-third of fats should come from saturated fats, with the other two-thirds split evenly between monounsaturated and polyunsaturated fat. It is estimated that in the average American diet (as of 2002), fats make up 42 percent of calories, with saturated fat making up between a third and a half of that amount.

The effects of this excess intake of dietary fat has some well-established implications for the health of overweight Americans. For instance, the consumption of excess amounts of saturated fats has been recognized as the most important dietary factor to increase levels of cholesterol. A high cholesterol level is detrimental to health and leads to a condition known as atherosclerosis. Atherosclerosis is the build-up of cholesterol on the walls of arteries, which may eventually result in the blocking of blood flow. When this occurs in the arteries of the heart, it is called coronary artery disease. When this process occurs in the heart, a myocardial infarction, or heart attack, may occur.

Besides the cholesterol implications due to high fat intake, obesity is a factor in the causation of disease. Being overweight or obese is highly associated with increasing the risk of type II diabetes, gallbladder disease, cardiovascular disease, hypertension, and osteoarthritis.

Fat-Replacement Strategies

The purpose of fat-replacement strategies is to reduce the percentage of fat in various foods, without taking away the appealing taste of the food. There are three broad categories of fat-replacement strategies: (1) adding water, starch derivatives, and gums to foods, (2) using protein-derived fat replacements, and (3) using engineered fats.

The addition of water to foods lowers the quantity of fat per serving in the selected food item. When starch derivatives are added to food, they bind

to the water in the food, thus providing a thicker product that simulates the taste and texture of fat in the mouth. Examples of specific starch derivatives include cellulose, Z-trim, maltrin, stellar, and oatrim. The problem with starch derivatives, however, is their limitations as a fat replacement in foods that require frying.

Protein-derived fat replacements are made from egg and milk proteins, which are made into a microscopic globule of protein. They give the sensation of fat in the mouth, although they contain no fatty acids. One such product is Simplesse, which is used mostly in frozen desserts. Because its chemical structure is easily destroyed by cooking or frying, its use is limited in most other foods.

The third fat-replacement strategy includes the use of engineered fats, which are made by putting together various food substances. One popular engineered fat is olestra, which is made by adding fatty acids to regular table sugar molecules (sucrose). This process results in a product that can neither be broken down in the digestive tract nor absorbed. It therefore cannot provide energy, in terms of carbohydrates or fatty acids,

to the body. Olestra is the first engineered fat to be used in fried foods. It does have its drawbacks, however. Olestra can cause abdominal cramping, loose stools, and it can bind beneficial substances that are normally absorbed, such as the fat-soluble vitamins (vitamins A, D, E, and K) and carotenoids.

In addition to fat-replacement strategies, there are low-fat or fat-free versions of many foods on the market. Some products made to be low-fat or fat-free include milk, yogurt, some cheeses, and deli meats. As a general rule, products that claim to have reduced amounts of fat should conform to the following stipulations: (1) a product labeled "reduced-fat" must have at least 25 percent less fat than the normal product, (2) a "low-fat" product can have no more than three grams of fat per serving, and (3) a "fat-free" product most have less than 0.5 grams of fat per serving. But one does not always need to look for foods made to contain less fat than normal, as there are plenty of natural foods that contain very little fat, or no fat at all, including most fruits and vegetables. Other foods that fit into the category of low-fat or nonfat foods include egg whites, tuna in water, skinless chicken, and pasta.

Foods that are low in fat are important for a healthful diet. While fats are essential components for bodily function, excess consumption of fats can lead to health problems such as obesity and heart disease. A healthful diet therefore consists of balanced proportions of proteins, fats, and carbohydrates.

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