title: Effects of high-fat and high-carbohydrate diets on metabolism and performance in cycling.
abstract: We compared the effects of high-fat and high-carbohydrate dietary conditions on metabolism and short- and ultra-endurance cycling performance. Seven cyclists (VO(2)max 72 +/- 7 mL x kg(-1) x min(-1)) underwent a 2-week adaptation to each of the following 3 diets: 14-day high carbohydrate with 70 +/- 9 percent energy (%E) carbohydrate, 16 +/- 5%E fat, and 14 +/- 2%E protein; 14-day high fat with 66 +/- 10%E fat, 20 +/- 3%E protein, and 15 +/- 4%E carbohydrate; and 11.5-day high-fat diet followed by 2.5-day carbohydrate-loading. The conditions included a pre-exercise meal of the same composition as the preceding diet. Each diet condition was preceded by a 2-week standardizing normal diet. The exercise test lasted approximately 5 hours and comprised a 15-minute trial, an incremental test to measure the peak fat-oxidation rate, and a 100-km trial. Sports bars and a 5% carbohydrate solution were ingested during the tests. The diets had no statistically significant effect on 15-minute performance, although the high-fat condition tended to reduce distance covered by -2.4% (95% confidence interval: -5.4% to +0.6%, P =.11) relative to the fat with carbo-loading condition. In the 100-km time trial, the high-fat and the fat with carbohydrate-loading conditions attenuated the decline in power output observed in the high-carbohydrate condition (P =.03 to.07), although the corresponding improvement in performance time of 3% to 4% (-2% to 10%) was not statistically significant (P =.16 to.22). Power output during the final 5 km of the time trial in the fat with carbo-loading condition was 1.3-fold (1.0 to 1.6, P =.04) greater than in the high-carbohydrate condition. Overall, for every 10%E increase in dietary fat, 100-km mean power increased by 2% (-0.0% to 4%, P =.06). Relative to the high-carbohydrate condition, the high-fat conditions resulted in the following metabolic changes consistent with greater lipolysis and fuel availability: lower plasma insulin concentration before exercise (P <.0001), and during exercise a 10% to 20% higher plasma-glucose concentration (P <.01), higher plasma glycerol (P <.05), and a 2.5-fold to 2.9-fold increase in the peak fat-oxidation rate (P <.0001). In conclusion, high-fat dietary conditioning increased fat oxidation, and although the main effects were not statistically significant, there was some evidence for enhanced ultra-endurance cycling performance relative to high-carbohydrate.
authors.affiliation: School of Physical Education and Department of Physiology, University of Otago, Dunedin, New Zealand.
authors.forename: David S
authors.initials: DS
authors.lastname: Rowlands
authors.forename: Will G
authors.initials: WG
authors.lastname: Hopkins
mesh_terms: D000328:Adult; D001786:Blood Glucose; D001835:Body Weight / Q000187:drug effects; D004040:Dietary Carbohydrates / Q000494:pharmacology*; D004041:Dietary Fats / Q000494:pharmacology*; D004734:Energy Metabolism / Q000187:drug effects* / Q000502:physiology; D005080:Exercise Test; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005934:Glucagon / Q000097:blood; D005990:Glycerol / Q000097:blood; D006801:Humans; D007328:Insulin / Q000097:blood; D019344:Lactic Acid / Q000097:blood; D050356:Lipid Metabolism; D008297:Male; D010084:Oxidation-Reduction / Q000187:drug effects; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology; D012016:Reference Values; D013997:Time Factors; D014508:Urea / Q000097:blood
chemical_list: D001786:Blood Glucose; D004040:Dietary Carbohydrates; D004041:Dietary Fats; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D019344:Lactic Acid; D014508:Urea; D005934:Glucagon; D005990:Glycerol