A study published in the August issue of the Journal of Nutrition (135:1903-1910) indicates that a weight-loss diet with a higher protein-to-carbohydrate ratio may promote greater fat loss and help preserve lean muscle mass compared to a diet with a higher carbohydrate-to-protein ratio.
Researchers investigated two diets—a high-protein, low-carbohydrate diet (PRO) and a low-protein, high-carbohydrate diet (CHO)—along with exercise, examining their effects on body composition and blood lipids in 48 women (average age 46, BMI 33 kg/m²). Both diets were equal in total energy (7.1 MJ/day) and lipids (30% of energy intake) but differed in protein content and carbohydrate-to-protein ratio: 1.6 g/day and <1.5 for the PRO group, versus 0.8 g/day and >3.5 for the CHO group. Participants either maintained an active lifestyle (control) or followed a supervised exercise program (EX) involving walking five days per week and resistance training two days per week. After four months, the PRO and PRO + EX groups lost more total weight and fat mass and showed a tendency to lose less lean mass compared to the CHO and CHO + EX groups. Exercise contributed to increased fat loss and lean mass preservation. The combined impact of diet and exercise was additive for improving body composition. Serum lipid profiles improved across all groups, but changes varied: CHO groups had larger reductions in total cholesterol and LDL cholesterol, while PRO groups experienced greater reductions in triacylglycerol and maintained higher HDL cholesterol levels. Researchers concluded that a higher-protein, reduced-carbohydrate diet combined with exercise additively enhances body composition during weight loss, though effects on blood lipids differ between dietary approaches.
