Background and Study Aim: One of the strategies for rapid weight loss among combat sports athletes is calorie restriction with consequent reduction of carbohydrate, which despite its efficacy has been an area of controversy. This study aim is the effects of a low carbohydrate diet on body composition, hormonal profiles and performance task in Brazilian jiu-jitsu (BJJ) athletes. Material and Methods: We performed a clinical study of which 18 BJJ athletes were randomised into two groups: a) low carbohydrate (L-CHO 2-3g/kg/day) and b) adequate carbohydrate (A-CHO 4-6g/kg/day). The nutritional status, body composition, hormonal profile (T3, T4, free-T4, thyroid stimulant hormone (TSH), insulin, cortisol and testosterone), muscle power of upper and lower limbs, anaerobic fatigue index and aerobic endurance were assessed before and after 30-days of nutritional intervention. Results: Regardless of the group, 88.9% achieved >3% of a weight loss and a decrement of body fat (>1.6%), however, A-CHO presented a significative loss of lean body mass (Delta = -3.9 kg). The L-CHO decrease de waist (Delta = -3.5 cm; p = 0.005) and hip circumferences (Delta =-2.0 cm; p = 0.009). The L-CHO group increased the blood TSH (Delta = 0.6; p = 0.046) and T4 (Delta = 0.6; p<0.033) and decrease insulin concentration (Delta = -2.9; p = 0.009). Conclusions: After 30 days, the diets of the L-CHO and the A-CHO group achieved similar weight losses for the BJJ athletes. However, the L-CHO group presented a better hormonal profile and quality of weight loss. The main findings showed differences between low and adequate carbohydrate diet evaluated after 30-days of intervention. Both groups reduced the daily intake of total calories and lipids, and gravity of the urine was remained hydrated before and after the nutritional intervention. After 30 days of training plus low carbohydrate diet, athletes preserved the lean body mass, reducing hostility, the waist and hip circumferences. Furthermore, insulin and thyroid hormones levels improved after the diet with low carbohydrates.
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