Low and high GI diet improves endurance performance, finds study
A recent Sports Medicine-Open study conducted a randomized controlled trial to evaluate how varying carbohydrate intake and the glycemic index (GI) impact performance in endurance training regimens in men.Carbohydrates are vital for endurance exercise performance, requiring optimal metabolic flexibility and glycogen stores. Muscles transition from fats to carbohydrates for ATP production...
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A recent Sports Medicine-Open study conducted a randomized controlled trial to evaluate how varying carbohydrate intake and the glycemic index (GI) impact performance in endurance training regimens in men.
Carbohydrates are vital for endurance exercise performance, requiring optimal metabolic flexibility and glycogen stores. Muscles transition from fats to carbohydrates for ATP production as exercise intensity rises. High-carbohydrate diets with low glycemic index enhance metabolic flexibility and boost performance.
The 10-week study aimed to assess and compare the effects of the low carbohydrates and high fat diet on metabolic parameters, running economy (RE), peak running speed (PRS), and peak oxygen consumption. These parameters were assessed by measuring muscle energy stores, a five-kilometer time trial (TT) performance, and a graded exercise test.
The results revealed that the LOW-GI diet led to reduced energy intake, decreased blood lactate concentrations during exercise, higher values in the graded exercise test, maintenance of glycogen stores, and improved TT performance. Further, HIGH-GI improved performance at high intensities and increased muscle glycogen content. However, after 10 weeks, fat oxidation was impaired.
Key findings are as follows:
- Total fat oxidation expressed as area under the curve (AUC) during the graded exercise test increased in LCHF (1.3 ± 2.4 g min−1 × km h−1), remained unchanged in LOW-GI and decreased in HIGH-GI (− 1.7 ± 1.5 g min−1 × km h−1).
- After the intervention, LOW-GI (− 0.4 ± 0.5 mmol L−1 × km h−1, p < 0.001) and low carbohydrate high fat (LCHF) (− 0.8 ± 0.7 mmol L−1 × km h−1) showed significantly lower AUC of blood lactate concentrations.
- Peak running speed increased in LOW-GI (T0: 4.3 ± 0.4 vs. T10: 4.5 ± 0.3 m s−1) and HIGH-GI (T0: 4.4 ± 0.5 vs. T10: 4.6 ± 0.4 m s−1), while no improvement was observed in LCHF.
- Time trial performance improved significantly in all groups.
- Muscle glycogen content increased for participants in HIGH-GI (T0: 97.3 ± 18.5 vs. T10: 144.5 ± 39.8 mmol L wet-tissue−1) and remained unchanged in the LOW-GI and the LCHF group.
- At the last examination, muscle glycogen concentration was significantly higher in LOW-GI compared to LCHF.
The findings suggested that relative to the LCHF or HIGH-GI diet, the LOW-GI diet could lead to beneficial changes in substrate oxidation during extended periods of exercise and improve endurance performance.
Reference: Moitzi, A. M., Krssak, M., Klepochova, R., et al. (2024) Effects of a 10-Week Exercise and Nutritional Intervention with Variable Dietary Carbohydrates and Glycaemic Indices on Substrate Metabolism, Glycogen Storage, and Endurance Performance in Men: A Randomized Controlled Trial. Sports Medicine - Open 10 ; 1-18. doi:10.1186/s40798-024-00705-9
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