4-Fats and Exercises

Nutrition and Fitness Prepared by Dr. Siham Gritly

Dr. Siham Gritly

Dr. Siham Gritly

Lipids and fats

• Introduction;-• *Lipids are chemical compound naturally

occurring substance; consist of carbon, hydrogen, and oxygen, widely found in plant and animal kingdoms. main foods contributing fats to our diet are butter, margarine, lard, vegetable oil, fat of meat, cream, milk, milk product, egg yolk, fish, poultry, nuts, seeds, olives, whole grain cereals.

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• A molecule of dietary fat consists of several fatty acids (containing long chains of carbon and hydrogen atoms), bonded to a glycerol. They are typically found as triglycerides (three fatty acids attached to one glycerol backbone).

• Fats may be classified as saturated or unsaturated depending on the structure of the fatty acids involved.

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exercise; discus role of Bile salt and fat digestion

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major functions of lipids in human body;

• *main source of energy, provide the body with 2/3 of energy (9 kal)

• *main source of fat soluble vitamins A, K, E D• *protection against traumatic injury an shock• *maintain body temperature• *provide pleasant feeling of satiety after a meal• *add to the palatability to diet• *help in formation of tissues and other important

organs in the body such as brain and bone marrow

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Classification of fats according to National Academy of Sciences

• Total fat, provide 20-35 % of total energy intake• Saturated fatty acids, risk of (Coronary Heart Disease

CHD) milk fat, coconut• Cis monounsaturated fatty acids, (olive oil) prevent

(CHD), peanut oil• Cis polyunsaturated fatty acids of two type health

benefit; fish oil, sunflower oil, corn oil, fish oil• 1-Omega 6 fatty acids• 2-Omega 3 fatty acids• Trans fatty acids, risk of (CHD), margin, shortening

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Exercise;

• discus the role of liver in fat metabolism

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Lipids and fats present in the body in three different forms

• 1-neutral fats (triglycerides)

• 2-cholesterol (present only in animal origin)

• 3-phospholipids (largest lipid components in the body)

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1-Triglycerides or neutral fat

• Triglycerides are the main dietary fats in human body. Triglycerides are alcohol glycerol and three fatty acids. The main fatty acids ;

• 1-stearic acid a (saturated fatty acid)• 2-oleic acid (unsaturated one double bond,

olive)• 3-palmitic acid (saturated, poultry, beef, milk,

palm oil)

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2-Cholesterols

• *Are member of groups called sterols, it is alcohol found only in tissues and cells of animals' origin.

• *main function of cholesterol;

• It enter in the formation of bile acids,• *Essential component of the structural membranes of all

cells especially brain and nerve cells• *They form a part of certain enzymes• *Enter in the formation of steroid hormones such as

esterogens, progesterone and testosterones • *Enter in the formation of vitamin D.

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3-phospholipids

• *phospholipids are any lipids containing phosphorus. they are the largest lipid components of the body after triglycerides

• *they form in all cells of the body • *in plasma, they are present in combination

with proteins and lipoproteins, which evolved in transport of fat and cholesterol

• *they form part of certain enzymes• *main constituents of all cell membranes

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• *example of phospholipids in the body;• -lecithin; neurotransmitter consist of glycerol, fatty

acids, phosphoric acid and cholin (nitrogen-containing base). found in liver, egg yolk, soy beans. the main function; transport and utilization of fatty acids with the action of enzyme as well as it prevent mental retardation.

• *cephalins; for blood clotting (thromboplastin)• *sphingomyelins; nerve tissues and brain, function act as

insulator around the verve fibers, found in egg yolk, liver.

• *glycolipids; serve tissues, cell membranes and help in fat transport.

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Fats and exercise

• *Fat is a great fuel for or survival but it is not adequate for high intensity exercise therefore fat is essential for longer, slower lower intensity and endurance exercise such as cycling and walking.

• *If exercising at a low intensity and enough stored fat available to fuel activity for hours or even days as long as there is sufficient oxygen to allow fat metabolism to occur.

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• *As exercise strength increases, carbohydrate metabolism takes over. It is more efficient than fat metabolism, but has limited energy stores.

• This stored carbohydrate (glycogen) can fuel about 2 hours of moderate to high level exercise.

• After that, glycogen depletion occurs (stored carbohydrates are used up) and if that fuel isn't replaced athletes performance may impaired

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• When carbohydrate intake is depleted, oxidation of fatty acids accelerate to provide energy through the production of acetyl CoA (TCA substrate)

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Using fat for fuel for exercise,

Some factors might affect using fat as fueling intense exercise

• 1-Fat is slow to digest and be converted into a usable form of energy but it can take up to 6 hours.

• 2-Converting stored body fat into energy takes

time. The body needs to breakdown fat and transport it to the working muscles before it can be used as energy.

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• 3-Converting stored body fat into energy takes a great deal of oxygen,

• -For these reasons, athletes need to carefully

time when they eat fat, how much they eat and the type of fat they eat. In general, it’s not a great idea to eat fat immediately before or during intense exercise

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Fat metabolism during exercise

• *People store large amounts of body fat in the form of triglyceride within adipose tissue as well as within muscle fibers.

• *These stores fat must be metabolize into FFA and transported to muscle mitochondria for oxidation during exercise.

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lipolysis (breakdown of lipids)

Energy utilization from Triglycerides (lipolysis)• *for energy utilization, triglycerides

breakdown or hydrolysis by the action of enzyme to fatty acids and glycerol, transport to the active tissues for oxidation to energy.

• *The glycerol released from this reaction is water soluble and diffuses freely into the blood

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• -glycerols ; When entering tissue glycerols change by enzymes to glycerol 3phosphate the entering glycolytic pathway (glycolysis).

• -fatty acids; enter mitochondria only, in the

mitochondria degradation or break down of fatty acids occur.

• it combine first with carrier substance carnitine, the

fatty acids split from carnitine to be oxidize then enter Kerb's cycle for energy production

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• At rest, about 70% of the FFA released during lipolysis are reattached to glycerol molecules to form new triglycerides within the adipose tissues

• -During low-intensity exercise, this process is at the same time as the overall rate of lipolysis increases; as a result, the rate of appearance of FFA in the plasma increases.

• Once they enter the plasma, the FFA molecules are loosely bound to albumin, a plasma protein, and transported in the circulation.

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lipogenesis (building of lipids)

• *lipogenesis is the process of fat formation and building up inside the body.

• *the liver is the main organ where lipids formed as it contain enzymes that needed during anabolism.

• *the liver enzymes resynthesize fatty acids and glycerol again to triglycerides.

 

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β oxidation of fatty acids

• *Beta oxidation is the process by which fatty acids, in the form of Acyl-CoA molecules, are broken down in mitochondria to generate Acetyl-CoA, then Acetyl-CoA entre to the Krebs Cycle for production of energy.

All acetyl Co A formed in metabolism occurs in the mitochondria

Formed from;

1-pyruvate oxidation

2-oxidation of fatty acids (β oxidation of fatty acid)

3-degradation of carbon skeletons of some amino acid

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*-Free fatty acids can enter into the plasma membrane due to their poor water solubility and high fat solubility. Once in the cytosol of the cell, a fatty acid reacts with ATP to give a fatty acyl adenylate, plus inorganic pyrophosphate.

*-This reactive acyl adenylate then reacts with free Co-enzyme A to give a fatty acyl-CoA ester plus AMP

*-The fatty acyl-CoA is then reacted with carnitine to form acyl-carnitine, which is transported across the inner mitochondrial membrane by a translocase enzyme in the membrane.

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Steps of beta oxidation of fatty acids in mitochondria

1-in mitochondria; by series of chemical reaction, fatty acid combined with acetyl Co A and then converted to fatty acyl Co A, (loss of carbon) this step need ATP.

2- fatty acyl Co A losses 2 hydrogen atoms leaving double bond. the hydrogen atoms combine with flavoprotein (FAD) to be oxidized later.

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3-water (H2O) react at all site of double bond

4-2hydrogen atoms are removed, leaving double bond. hydrogen combine with NAD (nicotinmide adenine dinucleotide).

5-the split of fatty acid between the α and β carbon produce long and short chain of fatty acid

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6-short chain combine with original Acetyl Co A and enter Kerb's cycle for more energy extraction.

this process is repeated until all fatty acids is split into acyl C0 enzyme A.

Co-A enter Citric acid cycle combine first with oxaloacetate to form citric acid and later degradation to carbon dioxide and hydrogen atoms.

Co-A +oxaloacetate---citric acid

final breakdown of FA is the same as that of acetyl Co-A formed from pyruvic acid during glucose oxidation

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steps of the formation of Acetyl CoA (β oxidation of fatty acids

1- Dehydrogenation by FAD: The first step is the oxidation of the fatty acid by Acyl-CoA-dehydrogenase. The enzyme catalyzes the formation of a double bond between the C-2 and C-3. enzyme acylCoA dehydrogenase.End product trans-2-enoyl-CoA

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2- Hydration: The next step is the hydration of the bond between C-2 and C-3. Enzyme enoyl CoA hydratase End product L-β-hydroxy-acyl CoA

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3- Oxidation by NAD+: The third step is the oxidation of L-β-hydroxyacyl CoA by NAD+. This converts the hydroxyl group (COOH) into a keto group (CH3-CO-CH3). Enzyme hydroxy-acyl CoA dehydrogenase,end product β-ketoacyl CoA

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4-thiolysis-: The final step is the cleavage of β-ketoacyl CoA by the thiol (ketone) group of another molecule of Co A. Enzyme β-Ketothiolase. end product An acetyl CoA molecule, and an acyl CoA molecule,.

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Integration of metabolic pathwaysFatty acid oxidation occurs in the mitochondria , feeds acetyl CoA into citric acid cycle and NADH/FADH2 into the electron

transport chain.

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Formation of Ketone bodies

Ketone bodies are names given to acetoacetate, β-hydroxybutyrate and acetone.

Serve as source of energy or fuel to peripheral tissues. It is the overflow pathway for acetyl CoA

Acetoacetate and β-hydroxybutyrate are transported by the blood to peripheral tissues, where they can converted back to acetyl CoA and oxidized through TCA cycle.

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• Normally the concentration of ketone bodies in the blood is very low,

• some times ketone bodies reach high level when fatty acid oxidation increase

• Increase in ketone body formation result in a condition known as ketosis

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• *if the concentration of acetoacetic acid and β hydroxybutyric rises to as high as 30 mg % above the normal (3mg %), thus leading to extreme acidosis.

• *acidosis is a condition where the pH of the blood is below normal (pH 7.35). pH is a value expressing the concentration of hydrogen ions in the blood, the accumulation of ketone bodies can disturb the body' acid-base.

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• When carbohydrate intake is low, oxidation of fatty acids accelerate to provide energy through the production of acetyl CoA (TCA substrate)

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references

• Sareen Gropper, Jack Smith and James Groff, Advanced Nutrition and Human Metabolism, fifth ed. WADSWORTH

• Melvin H Williams 2010; Nutrition for Health, Fitness and Sport. 9 th ed, McGraw Hill

• • Heymsfield, SB.; Baumgartner N.; Richard and Sheau-Fang P. 1999. Modern

Nutrition in Health and Disease; Shils E Maurice, Olson A. James, Shike Moshe and Ross A. Catharine eds. 9th edition

• Ellie Whitney and Sharon Rady Rolfes; Under standing Nutrition, Twelfth Edition. 2011, 2008 Wadsworth, Cengage Learning

• Guyton, C. Arthur. 1985. Textbook of Medical Physiology. 6th edition, W.B. Company

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Saturated fat

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Mono-saturated fat

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Polyunsaturated

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Saturated and trans fatty acids have

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Trans and cis fatty acid

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Lipoproteins found in the blood