New review of studies about effects of pre-exercise macronutrient composition on metabolism and performance, the metabolic and performance effects of consuming caffeine and beetroot juice.
Consuming a CHO-rich meal in the hours prior to endurance exercise appears to benefit performance. Performance may also be improved, or at least does not seem to be impaired, by ingesting CHO within 60 min of exercise. The effect of modified starches, such as Vitargo® (fast-digesting) and UCAN® (slow-digesting), is dependent primarily on the manner in which the starch is modified. Starches modified for the purpose of rapid digestibility can initiate rapid glycogen resynthesis, thus yielding potential performance benefits in repeated exercise. In contrast, starch modification for the purpose of slow-digestibility has been shown to increase fat oxidation during exercise compared to high-GI CHO, thus helping to preserve muscle glycogen; however, significant performance benefits have not been shown to date. High fat meals may enhance fat oxidation during subsequent exercise, although the performance effects are unclear, with most studies reporting no benefit or decrement versus a CHO meal. There are very few studies analyzing the performance effects of pre-exercise CHO-PRO meals, although there is some evidence suggesting potential enhanced glycogen storage and during exercise metabolism. Finally, caffeine and beetroot juice (dietary nitrates) appear to enhance performance, although these effects may be modulated by genetic factors and/or training status. More research is warranted to elucidate the effects of pre-exercise PRO, fat and modified starch consumption, as well as the effects of different pre-exercise and during-exercise nutritional combinations.
Ormsbee, M. J., Bach, C. W., & Baur, D. A. (2014). Pre-Exercise Nutrition: The Role of Macronutrients, Modified Starches and Supplements on Metabolism and Endurance Performance. Nutrients, 6(5), 1782-1808.