LIPIDS

LipidsEssential macronutrients Provide energy Building blocks for cell membranes Form many important hormones Help transport fat-soluble nutrients Contribute to flavor and texture of food Often used in cooking

Two unrelated types: Only thing they have in common: Hydrophobic

Lipids


1. Fats and Oils: Fatty acidsDiglyceridesTriglyceridesPhospholipids

Lipids



2. Sterols: Cholesterol and its derivatives

Lipids




Lipids

Fuel molecules to provide and store energy. Major part of cell membranes.

Form steroid hormones, bile salts, vitamin D.

Lipids: Fats and OilsBasic unit = Fatty Acid:

Long chains of carbons(always even number)bonded to hydrogens with carboxyl group at one end.



When metabolized, fatty acids are excellent sources of energy, but Many fatty acids are also important structural molecules and play important roles in regulating body processes.



Not all fatty acids are the same:2 - 4 carbons = “short chain” fatty acid6-10 carbons = “medium chain” fatty acid12 or more carbons = “long chain” fatty acid



If all carbons single-bonded to each other: SaturatedIf two or more carbons double-bonded: Unsaturated



If all carbons single-bonded to each other: SaturatedIf two or more carbons double-bonded: Unsaturated

Let’s take a closer look at unsaturatedfatty acids

Lipids: Fats and OilsBasic unit = Fatty Acid:If two or more carbons double-bonded: Unsaturated

One pair of carbons Two or more pairs of double-bonded: carbons double-bonded: Monounsaturated Polyunsaturated

Lipids: Fats and OilsBasic unit = Fatty Acid:If two or more carbons double-bonded: Unsaturated

Depending on the arrangement of the double bonds in either monounsaturated or polyunsaturated fatty acids, they are classified as either

cis-unsaturated trans-unsaturated fatty acids fatty acids

Lipids: Fats and Oils

Lipids: Fats and OilsWhy should we care if fatty acids in our diet are Saturated or unsaturated? Monounsaturated or polyunsaturated? Cis-unsaturated or trans-unsaturated??

Lipids: Fats and OilsWhy should we care if fatty acids in our diet are Saturated or unsaturated? Monounsaturated or polyunsaturated? Cis-unsaturated or trans-unsaturated?

Unsaturated fatty acids decrease the risk of heart disease, cancer, and other diseases.

Polyunsaturated fatty acids are best

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Lipids: Fats and OilsWhy should we care if fatty acids in our diet are Saturated or unsaturated? Monounsaturated or polyunsaturated? Cis-unsaturated or trans-unsaturated?

Trans fatty acids increase the risk of heart disease, diabetes, Alzheimer’s disease, and other diseases

“Hydrogenation” is used to stabilize & preserve food butincreases the trans fatty acids

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Lipids: Fats and OilsThus: USDA and DHHS recommend: Minimizing the amounts of - saturated fatty acids - trans saturated fatty acids and Increasing the percentage of fats containing polyunsaturated fatty acids

Lipids: Fats and OilsFatty acids are obtained from many foods, and the human body is able to synthesize most of them.

However, certain fatty acids must be obtained in the diet.

We defineNonessential fatty acids as those not needed in the dietEssential fatty acids as those needed in the diet

Lipids: Fats and OilsFatty acids are obtained from many foods, and the human body is able to synthesize most of them.

However, certain fatty acids must be obtained in the diet.

We defineNonessential fatty acids as those not needed in the dietEssential fatty acids as those needed in the diet

Be careful! Don’t confuse “nonessential” with “nonimportant”Many nonessential fatty acids are very important

Lipids: Fats and OilsThere are two essential fatty acids for humans:

Neither can be synthesized byhuman cells

Lipids: Fats and OilsThere are two essential fatty acids for humans:

These are examples of “omega-6” and “omega-3” fatty acids, and they are used as precursors to synthesize other beneficial fatty acids

Neither can be synthesized byhuman cells

Other important omega-3 fatty acids (which can be in the diet or synthesized from linolenic acid) are eicosapentanoic acid (EPA) and docosohexanoic acid (DHA)


Other important omega-3 fatty acids (which can be in the diet or synthesized from linolenic acid) are eicosapentanoic acid (EPA) and docosohexanoic acid (DHA)


From the Mayo Clinic: “There is evidence from multiple studies (that) recommended amounts of DHA and EPA in the form of dietary fish or fish oil supplements lowers triglycerides, reduces the risk of death, heart attack, abnormal heart rhythms, and strokes in people with known cardiovascular disease, slows the buildup of atherosclerotic plaques ("hardening of the arteries"), and lowers blood pressure slightly. However, high doses may have harmful effects, such as an increased risk of bleeding.”

Health benefits of omega-6 fatty acids are less defined:

- Known to be necessary for normal skin and hair growth - Known to be necessary for normal brain function - Linked to healthy bone growth


Health benefits of omega-6 fatty acids are less defined:

- Known to be necessary for normal skin and hair growth - Known to be necessary for normal brain function - Linked to healthy bone growth


From the University of Maryland: “Omega-6 fatty acids may be useful for the following health conditions:Diabetic neuropathy, Rheumatoid arthritis, Allergies, Breast cancer, High blood pressure (Hypertension), & Menopausal symptoms, (However), some omega-6 fatty acids tend to promote inflammation. In fact, some studies suggest that elevated intakes of omega-6 fatty acids may play a role in Complex Regional Pain Syndrome.”

Sources of omega-3 fatty acidsSoybean, canola, walnut, flaxseed oilsSalmon, tuna, mackerel, fish-oil supplements

Sources of omega-6 fatty acidsSeeds, nuts, vegetable oilsMeat, poultry, eggs

Diglycerides and Triglycerides

Lipids: Fats and OilsFatty acids, however, are very rarely found alone in either the diet or the human body.

Instead, they are linked together with a molecule called glycerol to form diglycerides and triglycerides, and they can be further modified to form phospholipids

Lipids: Fats and OilsAll those carbons, however, take a lot of time to draw, so we will begin using the abbreviatons used in your book:

Diglycerides

Triglycerides

Phospholipids

=

=

=

Structure: Glycerol + two fatty acids Glycerol + three fatty acidsHydrophobic = does not dissolve in water

Functions:Energy reserve – primarily in adipose tissue 15% - 30% of body mass = fat; 95% = triglycerides Fatty acids detached & metabolized: 9kcal/gInsulation under skin Protection (visceral fat surrounding organs)Carrier of fat-soluble vitamins

Diglycerides and Triglycerides

Structure: Glycerol + two fatty acids + phosphate groupAmphipathic: Phospate (“head”) group hydrophilic Fatty acids (‘tails”) hydrophobic

FunctionsPrimary component of cell membranesLipid transport as part of lipoproteinsEmulsifiers

Phospholipids

Food sources:Meat, egg yolks, liver, soybeans, peanutsModerate amounts in all foods

Phospholipids

Recall: Two unrelated types:

Only thing they have in common: Hydrophobic



Lipids

Sterols: CholesterolFunctions:

Component of cell membranesPrecursor to other substances

Vitamin DSteroid hormonesBile salts

Synthesized in the liver

Sterols in food:Found only in animal foods

Lipids in the DietRecommended intakes:

Total fat: 65 g/day (~20-35% of calories) Essential fatty acids: Linoleic acid – 12 g/day Linolenic acid – 2 g/day Saturated fats: <20 g/day Cholesterol: <300 mg/day

Lipids in the DietThe Facts Panel of all foods must include the total grams of fat and percentage of daily value based on a 2,000 kcal/day diet.

Lipids in the DietThe Facts Panel of all foods must include the total grams of fat and percentage of daily value based on a 2,000 kcal/day diet.

If that “total fat” number is not “0”, it must also include the amounts of saturated fat, trans fat, & cholesterol.(It may, but is not required to, also list amounts of monounsaturated and polyunsaturated fats.)

Lipids in the Diet

If that “total fat” number is not “0”, it must also include the amounts of saturated fat, trans fat, & cholesterol.(It may, but is not required to, also list amounts of monounsaturated and polyunsaturated fats.)

If that “total fat” number is not “0”, it must also list the recommended daily intake for total fat, saturated fat, and cholesterol

The Facts Panel of all foods must include the total grams of fat and percentage of daily value based on a 2,000 kcal/day diet.

Lipid DigestionDigestion of diglycerides and triglycerides

Lipid Absorption

Lipid AbsorptionSummary:

- Short-chain and medium-chain fatty acids are absorbed into the blood and carried to the liver bound to proteins.

Lipid AbsorptionSummary:

- Short-chain and medium-chain fatty acids are absorbed into the blood and carried to the liver bound to proteins.

- Cholesterol, long-chain fattyacids, monoglycerides, diglycerides, and triglycerides(re-formed by intestinal cells) are absorbed into lymphatic fluid and carried to cells all around the as part of chylomicrons.

Lipid Absorption

These chylomicrons “hide” the hydrophobic lipids in the center, surrounded by amphipathic phospholipids and proteins.

Thus, they are a form of lipoprotein.

Lipid Absorption

These chylomicrons “hide” the hydrophobic lipids in the center, surrounded by amphipathic phospholipids and proteins.

Thus, they are a form of lipoprotein.

There are three other types of lipoproteins which carry hydrophobic lipids from one place to another in the body

Lipids in the BodyVery-low-density lipoproteins (VLDL)

Deliver triglycerides to cells

Low-density lipoproteins (LDL)Deliver cholesterol to cells

High-density lipoproteins (HDL)Pick up cholesterol for removal or recycling

LIPIDS

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