Fat in exercise

“Success usually comes to

those who are too busy to

be looking for it”- Henry David Thoreau

NDD 30503

LECTURE 5

Fat as a Fuel for Exercise

DR. SHARIFAH WAJIHAH WAFA BTE SST WAFA & HH04

MONDAY (10 OKTOBER 2016), 2:00-4:00PM

SCHOOL OF NUTRITION AND DIETETICS . FACULTY OF HEALTH SCIENCES

TOPIC LEARNING OUTCOMES

Explain fat metabolism during exercise

Differentiate Long-Chain Triglycerides vs. Medium-Chain Triglycerides

Discuss the interaction of fat and CHO metabolism during exercise

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Introduction

• Primary fuels for exercise: fat & CHO

– Both fuels are oxidized simultaneously

– Proportion of each dependent on: • Meal prior to exercise

• Energy fed during exercise

• The duration, intensity, and type of exercise

• Athlete’s fitness level

– Fat becomes the primary source of fuel during endurance exercise


Introduction

• AMDR: 20-35% of kcal from fat

– Endurance athletes: moderate-to-low-fat diets (20-25% of kcal from fat)

– Ultralow-fat diets (<15% of kcal from fat) are not advantageous to health or performance and are difficult to follow

Function,

Classification, and

Dietary Sources of Fat


Important Roles of Fat

• Fat is essential to life:

– Primary source of energy at rest and during exercise

– Efficient way to store extra energy in a small space

– Provides essential FAs (linoleic and α-linolenic acid) and fat-soluble vitamins (A, D, E, K)


Important Roles of Fat

• Fuel for cells

• Organ padding and protection

• transport fat-soluble vitamins

• Constituents of cell membranes

• Constituents of hormones


Classification of Dietary Fats

• Dietary fats can be classified based on:


Saturated Fat

• Lacks C-C double bonds

• Saturated with H

• Animal fat & tropical oils

• Most unhealthy

• Hydrogenated oils


Monounsaturated Fat

• Contains single C-C double bond

• Most healthy

• Most common

– Olive oil

– Canola oil

– Peanut(s) oil

– Walnuts

– Almonds


Polyunsaturated Fat

• Two or more C-C double bond

• Omega 3

– Flax oil, Fish oil

– -linolenic acid

• Omega 6

– Corn, soyben, safflower, sunflower

– Linoleic acid


Hydrogenated Fats

• Process used to convert unsaturated oils into saturated oils

– Increases temp at which oil burns

– Increases shelf life

– Stays in mixture better

• Health impact is same as saturated fats


Trans Fatty Acids

• Formed from hydrogenation process

• May have worst health impact of all fats


Fatty Acids by Chain Lengths

• Short Chains– 6 or less carbon atoms

– Found in butter, coconut oil, palm kernel oil

• Medium Chain– 8 or 10 carbons

– Absorbed into blood more quickly

• Long Chain – 12 or more carbons, most are 16 and 18

– Most common in the diet


Fats in Foods

• Dietary fat is found primarily in the form of _______

– 3 FAs attached to a glycerol backbone

• Foods also contain other forms of lipids:

– Cholesterol, phospholipids, sterols

• Animal fats: provide ~40-60% of their energy as SFAs and 30-50% as MUFAs and PUFAs

• Plant fats: provide ~10-20% of their energy as SFAs with the rest from MUFAs & PUFAs


Fats in Foods

• Visible Fats

– Obvious fats that are easy to spot in foods

– E.g. oils, butter, cream, margarine, mayonnaise, fats on meats

• Invisible Fats

– Incorporated into prepared foods and are not as easily discernible

– Majority of fat in most people’s diet comes from invisible fats

– E.g. cookies, cakes, croissants, casseroles


Nutrition Labels: Fat Terminology

• Fat free: less than 0.5 g of fat per serving

• Low fat: 3 g or less of fat per serving

• Reduced or less fat: at least 25% less fat as compared to a standard serving

• Light: one-third fewer calories or 50% less fat as compared with a standard serving size

Body Fat Reserves

and Dietary Fat Intake


Body Fat Reserves

• Compared to protein & CHO stores, the body’s fat reserves are almost unlimited

• Total amount of energy stored as fat varies with an individual’s size and body fat percentage


Dietary Fat Intake of Active Individuals

• Intake of fat is variable depending on the sport and gender of the athlete– Athletes typically report consuming about 35% of their energy from fat

(Hawley et al. 1995)

• Endurance sports:– E.g. running, cycling, x-country skiing

– Report lower fat intakes and higher CHO intakes than sprinters and field event athletes

• Athletes with weight concerns:– E.g. sports that have ‘weigh ins’

– Lower fat intakes, esp. during periods of kcal restriction

Fat Metabolism During Exercise


Key Terms

• Lipolysis

• Triglycerides (triacylglycerols)

• Glycerol

• Gluconeogenesis

– Lactate

– Glycerol

– Alanine

• 3500 kcal = 2.2 kg fat


Sources of Triglycerides/Fatty Acids for Fuel

• Adipose tissue

– 64 kg @ 3% fat = 20,000 kcal

– 127 kg @15% fat = 170,000 kcal

• Muscle Triglycerides

– 2,000 - 3,000 kcal

– Supplies energy at 1/3 rate of CHO

• Plasma triglycerides

– Minimal contribution (40 kcals)


Characteristics of Fat That Make It Preferential to CHO as a Fuel Substrate

Reserve

• 2+ X as much energy per gram

• Not hydrated when stored

– 3 g H2O per g glycogen

– Equivalent energy as glycogen would increase body weight by 50% or more


Adipose Fat Tissue

• Adipose fat tissue contains the largest reservoir of stored energy within the body

• Steps involved to use fat during exercise:1. Breakdown of TGs to FFAs and glycerol

2. Mobilization and transport of FFAs within the fat cell

3. Transport of the FFAs out of the fat cell to the blood

4. Transport of the FFAs in the blood

5. Transport of the FFAs into the muscle cell

6. Transport of the FFAs to the muscle mitochondria

7. Oxidation to energy via the tricarboxylic acid (TCA) cycle


Lipolysis

• Lypolysis: the breakdown of fat in the adipose or muscle tissue to FFAs and glycerol– Metabolic process is initiated when the sympathetic nervous system

stimulates production of hormone-sensitive lipase (HSL) andepinephrine


• Re-esterification: FAs released during the process of lipolysis are re-esterified if they are not needed for energy at that time

– 3FFAs + glycerol are transformed back into a TG

– Intracellular recycling: re-esterification takes place within the adipose cell

– Extracellular recycling: re-esterfication takes place outside of the adipose cell (e.g. in the liver)

– During exercise, re-esterification is suppressed at the same time that the rate of lipolysis is accelerated

Re-Esterification


FFA Availability

• At rest, 70% of all FFA released during lipolysis are re-esterified.

• During exercise, re-esterification is suppressed by 50% which increases FFA availability.

• Exercise increases lipolysis (300%) which contributes to the plasma FFA.

• Blood flow to adipose tissue and to muscle is increased increasing overall delivery of FFA


• Sympathetic nervous system

– Strong stimulator of lipolysis

– Hormones: epinephrine and norepinephrine rise dramatically upon the initiation of exercise

– Signal the breakdown of stored fat (in adipose & muscle tissue) and carbohydrate (in liver & muscle glycogen), making these fuels available to the working muscles

• Other hormones that stimulate lipolysis:

– Growth hormone, cortisol, thyroid stimulating hormone

Hormonal Control of Lypolysis


• Insulin:

– Strongest inhibitor of lipolysis by decreasing the amount of active hormone-sensitive lipase (HSL)

– During exercise or times of starvation, when the need for fat as an energy source is high, insulin levels are typically low and lipolysis is high

Hormonal Control of Lypolysis


• Protein carrier mediated process

• Carriers become saturated at high plasma FFA levels (1.5 mmol/liter)

• Muscle contraction increases the activity of the carriers which increases the transport of FFA into the cell.

FFA Transport into Muscle


• Fat stored within skeletal muscle is an important energy source during exercise

– the fat is close to the mitochondria, the site of lipid oxidation and energy production, without requiring transport through the blood

Intramuscular Fat


Intramuscular Triglycerides (IMTG)

• Type I muscle fibers have higher concentrations.

• Endurance training translocates the IMTG next to the mitochondria

• Lipolysis of IMTG mediated by HSL and inhibited by insulin, just like in adipose tissue.


Substances providing energy during exercise at a given absolute intensity of 65% VO2max before and after 12 weeks of training.


Fat Oxidation and Exercise Duration

• Fat oxidation increases as duration increases

• Maximal oxidation rates are approximately 1.5 g/min.

• Fat oxidation increases probably because glycogen goes down.


Fat Oxidation and Exercise Duration

• During prolonged exercise there is a shift from CHO metabolism toward fat metabolism

• Increased rate of lipolysis

– Breakdown of triglycerides into glycerol and free fatty acids (FFA)

– Stimulated by rising blood levels of epinephrine


Shift From CHO to Fat Metabolism During Prolonged Exercise


Effect of Exercise Duration on Muscle Fuel Source


Fat Oxidation and Intensity

• Fat oxidation rates peaks at ~ 60-65% VO2max and then declines

• At low intensities (25% VO2max), most fat is from adipose tissue

• At 65% VO2max, most is from IMTGs

• At high intensities, fat oxidation is suppressed


Why is Fat Oxidation Suppressed at Higher Exercise Intensities?

• Reduced blood flow to adipose tissue due to sympathetic constriction of vessels

• Lactate increases re-esterification of FAs

• Transport into mitochondria is reduced


Interaction of Fat and CHO Metabolism During Exercise

• Some carbohydrate must be present in order for fat to be metabolized.

• Physiologic strategy: do what is necessary to “spare” carbohydrate.


Interaction of Fat and CHO Metabolism During Exercise

• “Fat burns in the flame of carbohydrates”

• When glycogen is depleted during prolonged high-intensity exercise

– Reduced rate of glycolysis and production of pyruvate

– Reduced Krebs cycle intermediates

– Reduced fat oxidation

• Fats are metabolized by Krebs cycle

Recommended

Consumption of Dietary Fat


Recommended Consumption of Dietary Fat

• Essential fatty acids must be supplied in the diet

– Linoleic acid (omega-6 fatty acid)

• 3-6 grams per day

• Supplied if 5-10% of calories are from fat

– Sources

• 1 tablespoon of corn oil

• 2 tablespoons of sunflower oil

• 2.5 tablespoons of canola oil

• 5 tablespoons of olive oil


Recommended Consumption of Dietary Fat

• Alpha-linolenic Acid (omega-3 fatty acid)– 1-2% of kcal consumption

– 2-3 grams for 2000 kcal diet

– Sources• 1.5 teaspoons Flaxseed oil

• 1.5 tablespoon canola oil

• 3 tablespoons soybean oil

• 12 oz cod, flounder, haddock, halibut, tuna

• 6 oz salmon

• 3.5 oz herring, mackerel, sardines


Daily Recommendation for Fats

• Less than 30% of total calories for most

• Less than 10% of calories as saturated fat

• Adequate essential fats

• Most fat should be monounsaturated with polyunsaturated as second choice


Fat Supplementation During Exercise

• Cannot consume FFA because they are too acidic and require protein carrier for absorption

• LCT are slowly absorbed and rate of uptake by muscle is slow

• MCT are directly absorbed and easily transported into muscle– 30 g is limit of tolerance

– Practically can contribute no more than 10% of total energy


Short-Term Dietary Fat Supplementation Before Exercise

• Consuming high fat diet increases fat utilization but reduces exercise intensity that can be tolerated

• Consuming high GI CHO just prior to exercise will inhibit fat utilization during first 50 min of exercise and increase use of blood glucose


Long-Term High-Fat Diet and Exercise Tolerance

• Exercise duration may be increased at intensities <65% VO2max

• Durations at competitive intensities are not improved


Combined Fat and CHO Loading

• No demonstrated beneficial effect of combining high fat diet in days before exercise and CHO loading immediately before exercise.


Fat Intake During Recovery

• Requires 2gm/kg to resynthesize IMTG

• Take ~ 22 hrs to resysnthesize

• Optimizing IMTG may compromise CHO


Carnitine Supplementation

• Facilitates transport of LCT into mitochondria

• Found primarily in animal products, especially meat

• Consensus is that carnitine is not ergogenic

Syukran

Fat in exercise

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