[PPT]Fat: An Important Energy Source During Exercise · Web viewFats Functions of Fat Fuel for...
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Fats
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Functions of Fat
• Fuel for cells• Organ padding and protection• transport fat-soluble vitamins• Constituents of cell membranes• Constituents of hormones
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Categorization of Fats
• Degree of Saturation– Saturated– Monounsaturated– Polyunsatrated
• Chain Length– Short– Medium– Long
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Saturated Fat
• Lacks C-C double bonds• Saturated with H• Animal fat & tropical
oils• Most unhealthy??• Hydrogenated oils
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Monounsaturated Fat
• Contains single C-C double bond
• Most healthy• Most common
– Olive oil– Canola oil– Peanut(s) oil– Walnuts– Almonds
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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
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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
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Trans Fatty Acids
• Formed from hydrogenation process• May have worst health impact of all fats
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TABLE 5.1 Fatty Acids in fats and oilsOil/Fat Saturated Mono-unsat PolyunsatBeef 50 43 4Chicken 30 46 22Tuna 27 26 37Olive 14 74 9Canola 6 62 30Tuna 27 26 37Coconut 87 6 2
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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
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Key Terms
• Lipolysis• Triglycerides (triacylglycerols)• Glycerol• Gluconeogenesis
– Lactate– Glycerol– Alanine
• 3500 kcal = 1 lb fat
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Sources of Triglycerides/Fatty Acids for Fuel
• Adipose tissue– 140 lb @ 3% fat = 20,000 kcal– 280 lbs @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)
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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
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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 avaiability.
• 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
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FFA Transport into Muscle
• 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.
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Intramuscular Triglycerides (IMTG)
• Type I muscle fibers have higher concentrations.
• Endurance training translocates the IMTG next to the mitochondria
• Lipolysis of IMTG mediated by hormone sensitive lipase (HSL) and inhibited by insulin, just like in adipose tissue.
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Training
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Fig. 2. Contribution of the four major fuel substrates to energy after 30 min of exercise at 25%, 65%, and 85% of VO2max in fasted subjects.
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Fig. 4. Substances providing energy during exercise at a given absolute intensity of 65% VO2max before and after 12 weeks of training.
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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.
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Fat Oxidation and Intensity
• Fat oxidation rates peak at ~ 60-65% VO2max in trained (VO2max = 60 ml/kg/min) and then declines (range 50-85%)
• Fat oxidation rates range from 0.23 g/min to 0.91 g/min)
• 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
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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 the muscle is reduced• Breakdown of IMTG is reduced• Transport into mitochondria is reduced
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Muscle Adaptations Which Enhance Fat Use
• Increase in enzymes of beta-oxidation• Increase of ETS capacity• Increase sensitivity of SNS stimulation• Increase in transport mechanism across
sarcolemma and within muscle
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Systemic Adaptations Which Enhance Fat Use
• Decrease in insulin• Decrease in lactate• Increase delivery of substrate
– Cardiovascular– Capillarization
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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
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Short-Term Dietary Fat Supplementation Before Exercise
• Consuming high fat diet increases fat utilization but reduces or does not change 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
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Long-Term High-Fat Diet and Exercise Tolerance
• Exercise duration may be increased at intensities <65% VO2max
• Durations at competitive intensities are not improved
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Combined Fat and CHO Loading
• No demonstrated beneficial effect on performance of combining high fat diet in days before exercise and CHO loading immediately before exercise.
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Fat Intake During Recovery
• Requires 2gm/kg to resynthesize IMTG• Take ~ 22 hrs to resysnthesize• Optimizing IMTG may compromise CHO