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.
There is a popular belief that meat consumption is necessary to optimize adaptations to strength training (ST), but evidence to support this hypothesis is scarce. Therefore, this study aimed to compare ST adaptations in lacto-ovo-vegetarians (LOV) and non-vegetarians (NV) with adjusted protein intake per meal. Sixty-four LOV and NV performed 12 weeks of ST and were instructed to ingest at least 20 g of protein, in each main meal during the experimental period. Quadriceps femoris muscle thickness (QFMT), knee extension one-repetition maximum (1RM) and isometric peak torque (PT), as well as participants’ body composition were assessed before and after the intervention. Dietary intake was assessed throughout the study. After 12 weeks similar increases in QFMT (LOV: 9.2 ± 5.4; NV: 8.1±5.5mm), knee extension 1RM (LOV: 24.7±11.1; NV: 21.6±9.8 kg) and PT (LOV: 29.8±33.4; NV: 17.5±19.4 N.m) and lean body mass (LOV: 1.3±0.9; NV: 1.4±1.4 kg), alongside a decrease in body fat mass (LOV: -0.5±1.6; NV -0.8±1.6 kg), were observed in both groups at the end of the training period (p<0.05). LOV had lower protein consumption than NV throughout the study (p<0.05), but participants reached intake of at least 1.2 g of protein/kg/day during the experimental period. In conclusion, LOV and NV displayed similar improvements in muscle mass, strength and in body composition after 12 weeks of ST, suggesting that meat consumption and higher protein intake in NV did not bring about further benefits to early adaptations to ST.
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