Fat: An Important Energy Source for Exercise

The Dietary Fats

n Lipids

n Class of organic substances that are insoluble in water but soluble in alcohol and ether

n Types:

n Triglycerides

n Composed of glycerol + 3 fatty acids

n Saturated fatty acid (usually solid at room temp)

- all carbon atoms are filled by H⁺

n Unsaturated fatty acid (usually liquid at room temp)

- not all carbon atoms are filled by H⁺; have double bonds

The Dietary Fats

n Triglycerides (continued)

n The unsaturated fatty acids

n Monounsaturated – have single double bond

n Polyunsaturated – have 2 or more double bonds

n Omega-3 (3 places between 1^st C double bond and last)

n Omega-6 (6 places between 1^st C double bond and last)

n Partially hydrogenated fat (oil)

n Adding of H⁺ to polyunsaturated fat; becomes more saturated

n If H+’s on same side of double bond – cis

n If H+’s on opposite side’s of double bond – trans

Health Implications with Fats

n In general

n Avoid excess intake of saturated and trans fatty acids in diet

n Associated with increased health risks

n Adequate intake of mono-, poly-, and omega-3 unsaturated fatty acids should be included

n Associated with neutral or beneficial health

Hidden Fat

n Foods may contain a high amount of fat but is not visible – this is “hidden” fat

n Examples

n Whole milk, cheese, nuts, desserts, crackers, potato chips, and other commercially-prepared foods

Percentage of Fat Calories in Food

n Advertised percentage of food refers to the weight of the product, not caloric value

n Example

n Luncheon meat may be advertised as 95% fat-free but may contain 40% of its calories from fat

n Most of weight may come from water weight

n Foods with higher water content usually have higher caloric content also

n Example

- whole milk (3.5% fat by weight)

- fat accounts for 48% of its caloric content

Fat Substitutes

n Manufactured from CHO, protein, or fat

n Replace fat with less or no calories but provide the taste and texture of fats

n Generally recognized as safe by FDA

n Examples:

n Guar gum, cellulose gel, etc.

n Olestra

n A type of sucrose + fatty acids

n Can’t be digested or absorbed; hence 0 Calories

Types of Fats

n Cholesterol

n Not a fat, but a fat-like substance necessary for tissue structure; not an essential nutrient from diet, i.e. the body can make it

n Phospholipids

n Similar to triglycerides but contain a phosphate necessary for tissue structure; not an essential nutrient from diet

Why do we need fat in our diets?

n Meet energy needs

n Provide essential fatty acids

n Provide essential fat-soluble vitamins

n A, D, E, and K

n Consideration

n Low-fat diets are not recommended for children during their growing years

How much fat do we need in our diets?

n Fat intake should not be below 10-15% of our total daily calories

n 2 fatty acids are essential

n Linoleic acid

n An omega-6 fatty acid found in vegetable and nut oils (corn, sunflower, peanut, soy)

n Alpha-linoleic acid

n An omega-3 fatty acid found in green leafy vegetables, canola oil, flaxseed oil, soy products, some nuts, and fish

n The essential fatty acids should constitute 0.5-1% of daily energy intake (~ 1-3 grams)

Fat and Metabolism

n Fats are broken down into primarily triglycerides (95% of fat breakdown; 5% is sterols and phospholipids)

n Fatty acids can be taken up by the muscle and fat to be stored in the form of tryglycerides

n The liver is important in metabolizing various types of fats, including:

n VLDL (very low-density lipoprotein)

n LDL (low-density lipoprotein)

n HDL (high-density lipoprotein)

Can the body make fat from CHO and protein?

n Yes

n When there is an excess of CHO and protein, fat will be made (via acetyl CoA)

n Some evidence suggests that dietary fat may be stored more readily than excess CHO or protein as adipose tissue

n This may be a primary factor related to obesity

Major Functions of Body Lipids

n Structure

n Cell membranes and nerve tissue

n Metabolic regulation

n Cholesterol is component of several hormones, i.e. testosterone and estrogen

n Eicosanoids

n Fatty acid derivatives that may influence health and physical performance

n Derived from omega-3’s

n Energy source

n Primarily in form of triglycerides

Lipids as Energy Source

n At rest, ~ 60% of energy supply is from fat when consuming a mixed diet

n May be higher usage of fat when blood glucose levels are low

n Following a high fat meal, a greater amount of energy will be derived from fat

n Excess fat metabolism may result in formation of ketones

n Ketones are utilized as energy source during fasting or starvation

n Excess accumulation of ketones can lead to acidosis; this may be problem for individuals with diabetes

How much total energy is stored as fat in the body?

n Fat is very efficient and compact way to store energy

n 5-6 times more efficient as a storage fuel compared to CHO and protein

n Approximately 80,000 to 100,000 Calories of energy are stored as triglycerides in the average male

n Stored in:

n Muscle, blood, and liver

Fats and Exercise

n Major fat energy sources for exercise

n Muscle triglycerides

n Plasma FFA

n Meet the majority of fat energy needed at rest

n Greater uptake of FFA during exercise of low intensity

n As intensity increases to 65% effort, there is a greater use of muscle triglycerides

n Equal contribution from CHO

n Intensity higher than 65% effort, CHO becomes the predominant fuel source

Limitations to fat use during exercise

n Inadequate FFA mobilization from adipose tissue to the muscle

n Suboptimal intramuscular processes

n Use of CHO may inhibit carnitine-enzyme complex

n Carnitine-enzyme complex helps transport fatty acids into mitochondria for energy

n Increased presence of glucose

n Influx of insulin not only promotes glucose uptake by muscle but uptake of FFA by adipose tissue and muscle

Is there a gender difference in the use of fat during exercise?

n It appears that women may utilize more fat than men when exercising at 65-75% VO₂ max; not conclusive

n Estrogen may be the primary factor for the “favored” fat use by women

Exercise training effect on fat metabolism during exercise

n Fat is more readily utilized by trained athletes compared to untrained athletes, particularly at higher intensities up to 70-80% VO₂ max

n Become better “fat burners”

n Why?

n Increased blood flow and delivery of FFA to muscle

n Increased triglyceride content; i.e. fat stores in adipose tissue and muscle

n Increased sensitivity of both adipose tissue and muscle to epinephrine ( ↑ release of FFA to blood and within muscle)

Exercise training effect on fat metabolism during exercise

n Why better fat burning? (continued)

n Increased # of fatty acid transporters in muscle

n Improved ability to use ketones as an energy source

n Increased # and size of mitochondria; also ↑ activity of oxidative enzymes

n Increased activation of FFA & transport into mitochondria

Fats: Ergogenic Aspects

n Fat loading

n Increasing fat content in muscle and plasma to improve performance

n Acute high-fat diets

n Inject lipid solution (Intralipid) into blood, along with heparin to stimulate enzyme activity to release FFA into blood

n No definitive research findings on this; Tour de France race team withdrew from competition after trying this; apparent adverse reactions???

n Ingest high-fat meal 4 hours prior to exercise

n Not effective in improving endurance performance; may actually impair performance (1-2 days of high fat meals)

Fats: Ergogenic Aspects

n Fat loading

n Chronic high-fat diets

n 7-10 days of eating high fat meals (60-70% fat) has not been shown to improve endurance performance compared with high-CHO diets

n However, fat oxidation did increase in endurance-trainined athletes

n Adaptation to fat diet does not appear to affect rate at which muscle glycogen is used

n Additional studies needed, since earlier years of research suggested that fat loading might work (generally not well controlled studies)

Does fasting improve performance?

n Not likely

n Although fasting for 24 hours may increase FFA in the blood, endurance performance is usually impaired due to loss of muscle glycogen or a hypoglycemic state

Can medium-chain triglycerides (MCTs) improve performance?

n MCTs (have 6-12 C’s in their makeup) are water-soluble so can be absorbed and transported more easily

n This suggests potential more a more efficiently accessed energy source

n However, high-fat meals using MCTs have not been shown to improve performance

Can glycerol improve performance?

n Due to its slower conversion rate to glucose, in the liver, it has not been proven to be effective for endurance performance

n However, it may be used to increase body water stores prior to exercise which may improve cardiovascular function and regulate body temperature

Can wheat germ oil improve performance?

n Comes from embryo of wheat

n High in linoleic F.A., Vit E, octacosanol (a white alcohol theorized to be ergogenic)

n Octacol 4 was endorsed by a leading marathoner in U.S.

n Reported to improve endurance but not yet proven to be true

Can lecithin improve performance?

n Lecithin is a phospholipid contained in beans, eggs, wheat germ

n It is an important component of body tissues and helps in formation of Ach (neurotransmitter)

n Purported to increase strength and power

n Not shown to be effective

Can omega-3 fatty acids improve performance?

n Omega-3 fatty acids (found in fish):

n Are components of red blood cell membranes – make them less viscous and less resistant to blood flow

n Are components of eicosanoids (PGE₁ & PGI₂)

n Cause vasodilation & stimulate release of HGH

n Better delivery of O₂ and stimulate muscle growth

n Not proven to improve endurance performance or increase strength

Can carnitine improve performance?

n Carnitine is a water-soluble, vitamin-like compound

n Facilitates transport of long-chain fatty acids into mitochondria

n Beef and pork are good sources; also made in the liver from 2 amino acids (lysine & methionine)

n Acute supplementation (2 grams, 2 hours before event) does not improve endurance

n Chronic supplementation (6 grams/day, 7 days) does not improve anaerobic

n Its effect on VO₂ max is equivocal (not proven or disproven)

n Doesn’t enhance fat use or glycogen sparing

n D-carnitine may be toxic but L-carnitine appears to be safe (but no more than 2-5 grams/day, for 1 month at a time)

Can caffeine improve performance?

n A normal therapeutic dose is 100-300 mg

n 100-150 mg in cup of coffee; 20-50 mg in cup of tea; 35-55 mg in can of cola; 55-110 mg in can of high caffeine soda; 100-200 mg in tablet of Vivarin

n It is a CNS stimulant that enhances psychological processes

n It is a physiological stimulant

n Increases HR, blood flow, release of epinephrine (adrenaline)

n Enhances muscle contraction, ↑ muscle & liver breakdown, ↑ release of FFA from adipose tissue, ↑ use of muscle TG

Can caffeine improve performance?

n May have ergogenic effects

n IOC has set legal limit of < 12 mg per ml of urine for competition

n This would be equal to < 5-6 cups of strong coffee or < 4 Vivarin tablets in short period of time

n 800 mg consumed in 2-3 hrs would exceed limit

n Recommendation is 7 mg/kg or less to avoid positive drug test

Can caffeine improve performance?

n Potential effects

n Increased alertness; lessens perception of exercise effort

n May enhance performance in high-intensity exercise of trained athletes (e.g. 100 to 1,500 m swims, middle-distance runners) but most studies suggest that it is not effective

n May increase utilization of FFA during exercise

n It does cause a glycogen-sparing effect, which results in enhanced performance in events of one hour or longer duration; ~ 40-50% improvement

Is caffeine effect altered by other things?

n CHO loading does not appear to affect caffeine effect

n Caffeine may have lessened effect on caffeine users (regular) but not proven; some refrained from caffeine use 2-4 days prior to use

n Caffeine capsules may be more effective than coffee; more studies necessary

n Combined with ephedrine may enhance performance in short-term events but is not legal (possibly dangerous)

n As a diuretic, could increase water loss, however, not shown to impair performance; doesn’t ↑ urine production

Self-use of caffeine to enhance performance

n Suggestions:

n Use during training, initially, before using for competition

n Take 200-300 mg about 1 hour prior to workout

n Try placebo vs caffeine capsule

n Abstain from caffeine for 4-5 days prior to use

n Keep record of use and note feelings

Does exercise training provide beneficial effects to lipid profiles?

n Yes

n Benefits

n Lower plasma levels of triglycerides

n Lower plasma levels of LDL-C

n Higher plasma levels of HDL-C

n To achieve benefits

n Endurance exercise of 10-15 miles/week (~ 1,000 Cals/week)

n Endurance exercise should be held for 3-9 months

n When exercise training combined with good diet, benefits are improved