Effect of high-fat or high-carbohydrate diets on endurance exercise: a meta-analysis

Int J Sport Nutr Exerc Metab. 2005 Feb;15(1):1-14. doi: 10.1123/ijsnem.15.1.1.


The purpose of this investigation was to clarify, via a meta-analysis, whether the literature favors a high-fat or a high-carbohydrate diet to yield superior endurance exercise performance. Twenty published trials were analyzed to compare exercise performance under different diets. The average effect size of -0.60 indicated that subjects following a high-carbohydrate diet exercised longer until exhaustion. The training status of subjects (trained vs. untrained) was significantly related to effect size (r = -0.576, P < 0.01) and effect sizes separated between trained and untrained subjects were -0.05 and -2.84 respectively. The test for homogeneity revealed significant heterogeneity among effect sizes (chi2 [19] = 43.30, P < 0.05), indicating all of the trials are not describing the same effect. Given this significant heterogeneity, a conclusive endorsement of a high-carbohydrate diet based on the literature is difficult to make. Highly dissimilar trial protocols are the primary reason for heterogeneity.

Publication types

  • Meta-Analysis
  • Review

MeSH terms

  • Adaptation, Physiological
  • Bicycling / physiology
  • Dietary Carbohydrates / administration & dosage*
  • Dietary Fats / administration & dosage*
  • Female
  • Humans
  • Male
  • Oxygen Consumption
  • Physical Endurance / physiology*
  • Physical Fitness / physiology
  • Randomized Controlled Trials as Topic
  • Running / physiology


  • Dietary Carbohydrates
  • Dietary Fats