2 Remember... All energy systems are on at all times... At higher exercise intensities there is a shift toward carbohydrate use.At lower intensities <65% VO2max, FAT is oxidized to produce ATP.But “low intensity” doesn’t mean that carbohydrate use isn’t occurring...
4 Ultra-Distance Performance Times Endurance exercise performance is limited by an individual’s ability to sustain the desired intensity late in exercise.Example: Marathon TimeAlmost all available glycogen is gone, aa breakdown and liver glycogen useBeta (fat) oxidation, level of CHO oxidation depends on intensity and training status and CHO availabilityStart of aerobic CHO oxidationOne minute left KICKAnaerobic10s, 30s...1 min5 min20min 90min last 15min
5 Another approach to having “extra” glycogen – train your body to use less The alternative to maximizing the availability of CHO is to conserve CHO by maximizing the capacity to oxidize fat. The essential theory underlying this strategy is the reciprocal relationship between FAT and CHO in terms of providing energy for exercise.GlycogenTriglycerideGlucoseFree Fatty AcidPyruvateAcetyl-CoAFatty Acyl CoATCA (Krebs) cycle
6 3. intramuscular triglyceride stores and/or glycogen stores. There are several potential sites where the entry of fatty acids into oxidative pathways can be affected:1. entry of FFA into muscle by raising levels of FFA in blood.2. entry of FFA into mitochondria by raising activity of CPT-I (similar to GLUT4 but transports fat into the mitochondria).3. intramuscular triglyceride stores and/or glycogen stores.4. capacity of the TCA cycle overall.
7 Studies of performance after high fat diets Muoio et al (1994) gave 3 different diets (for seven days) in nonrandom order to 6 trained runners.Low CHO (LC): 40% CHO (6.6g/kg/d CHO)High CHO (HC): 70% CHO (9.7g/kg/d CHO)Normal (N): 60% CHOVO2 max and submaximal endurance were highest on low CHO diet BUT hard to interpret because there were only 6 subjects and diets given in nonrandom orderPogliaghi (1999) et al performed a similar study with 14 subjects (and random order) and found no differences in performance after 4 weeks of diets with varied macronutrient composition.Burke and Hawley (2001) report that 5-6 days of a high fat diet (2.4 g CHO/kg/d vs 9.6 g CHO/kg/d) increases fat oxidation (and glycogen sparing) during submaximal exercise but results show no clear benefits nor detriments to the performance of prolonged endurance exercise (though rate of perceived exertion was higher).
8 High Fat vs. High CHO p.144 CHO FAT Endurance Performance Time Baseline7 weeks2 weeks
9 High Fat Diet but very low CHO intake...Ketogenic Diets Many variations but key elements are:extremely low in CHO (<10% energy)extremely high in fat (>60% energy)protein varies a lot (10-40% kcal)Theoretical advantages for athletes:High fat content may intramuscular triglyceride storageCellular adaptations to access and oxidize intramuscular triglyceride may spare glycogenProduction and utilization of ketones may further spare CHO useImproved submaximal performance??
10 Short Term Low CHO/High FAT and Performance Langfort et al (1996)8 untrained men mixed or ketogenic (50% fat, 45 % protein, 5% CHO) diets for 3 days and measured performance and metabolic markers.Ketogenic diet did not lower VO2 max or lactate threshold.Ball et al (1996)6 healthy males cycle until exhaustion (at ~95% of max) after consuming a normal or ketogenic diet (33.6% pro, 64.4% fat and 2.2% CHO) for 3 daysExercise time following the low CHO diet was shorter than exercise time after 3 days of normal diet.
11 Long Term Hoppeler et al (2003) Highly trained du-athletes 5 weeks of high fat (~53%) or low fat (~13%) diets using a randomized cross over design.They reported no change in:maximal aerobic or power capacitymuscle glycogen levelsBut changes in:increased intramuscular triglyceride (after high fat diet)lower blood lactate and RER (after high fat)Overall: 2X increase in intramuscular triglyceride without compromising glycogen storesMetabolic data indicate shift toward a larger utilization of fat for energy: No effect on performanceLot of Variability between subjects
12 Summary of FAT Manipulations and Endurance Performance Studies 1. How low in CHO depends on total energy.2. Above a threshold (5g/kg/d??), no benefit of CHO on performance.3. Humans may have greater capacity to oxidize fat than often appreciated.4. Adaptations occur fairly quickly (< 7 days)
13 How can athletes maintain performance on CHO-restricted HIGH FAT DIET? 1. Increase IMTG = more fat use, conserve glycogen2. On high-FAT diets (less than 2g CHO/kg/day or >50% energy from fat), lack of CHO causes ketogenesisLow insulin levels= very high rates of lipolysis (breakdown ofTG to FFA in adipose tissue). In liver, FFA are oxidized, re-esterified, or converted to KETONESKetones can replace glucose usually required by brain (andother tissues).Ketones could help maintain performance byproviding an alternate energy source for brain (and muscle)that spares glycogen).Do diets work long-term? Beside the point - athletes do notuse them this way
14 Is the diet actually low in CHO? Some yes, some no, depends on the % of the diet that is CHO but ALSO the total number of caloriesIs muscle glycogen lower?Some yes, some no – depends on how low the diet really was in CHO and the duration/intensity of the training.Is performance compromised?Varies – partly due to lack of controlled studies – some show improved performance with high fat, others show no change, and other show worsening.There may be no “true” response to high fat diets that will hold true for 99% of the population.Many studies had very “person-specific” results. The fact thatthere were very different results from different subjects is animportant take home points Athletes, coaches, etc shouldrealize that each athlete may have a different response andthat just because the literature “says so” doesn’t mean thatone diet is the optimal diet for performance for everyone.
15 Fat Basics The average American consumes a diet that is about 30% fat. High fat diet has been associated with an increased risk of cardiometabolic disease.High fat diets are likely high calorie diets and increase ones chance for weight gain over time.Athletes, decrease their risk of cardiometabolic disease with regular exercise… they likely aren’t negatively effected by overeating fat.In fact, athletic performance could be affected by under-eating fat...
16 Fat is good... Fats are important for many metabolic processes: Energy productionTransporters of lipid soluble vitaminsImportant in the synthesis of Vitamin D, cholesterol, and steroid hormones.Structurally important in cell membranesFat can be classified by its structure:Unsaturated: contain double bonds between carbonsIncludes the essential fatty acids that must be consumed in our diet.Saturated: single bonds between carbonsLinked with cardiovascular disease, should be limited to less than 10% of total calories.
17 To little fat...<10%Risk of becoming deficient in essential fatty acids and fat soluble vitamins.Could affect fat mobilization and oxidation, important in energy productionLower circulating levels of hormones (insulin, testosterone...important ones if you want to build lean body mass)
18 Summary and Recommendations Athletes eating a diet of 55-65% CHO should consume 20-25% (30%?) fat.Limit intake of saturated fat“Good” fat sources:Olive oil/Canola Oil, Seeds, Nuts, Fish, AvocadoFor athletes who require high ENERGY intake,increasing fat in the diet can be helpful to maintainenergy balance
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