Influence of the Glycemic Index of Pre-exercise Meals in Sports Performance: A Systematic Review

Introduction: Carbohydrate (CHO) is essential for physical exercise. Some strategies for improving performance are based on the manipulation of the glycemic index (GI) of this nutrient during pre-exercise. Although several studies have been conducted on this subject, the use of low or high GI in a pre-exercise meal to improve performance remains undefined. Methods: In the present systematic review, the Pubmed (Medline) and Virtual Health Library databases were searched for randomized clinical trials conducted with healthy, physically active adults between 2006 and 2019, in which performance in addition to blood biochemical parameters, substrate utilization, body composition, perception of effort, and gastrointestinal symptoms were evaluated. The identified articles were independently and blindly evaluated by two authors, and any disagreements were resolved by a third investigator. Results: Five of the sixteen studies reviewed found differences in performance; of these, four were with low GI intervention. Few studies showed modifications in blood lactate and glucose levels beyond fatty free acid oxidation. No differences could be seen in the other parameters. The results as well as the methodologies used were heterogeneous; therefore, there are no clear advantages in determining the specific GI of the pre-exercise meal. Conclusions: There is no evidence that the pre-exercise meal GI influences performance. The heterogeneity of the studies precludes further conclusions.