Background: Limited evidence suggests that a higher ratio of protein to carbohydrate during weight loss has metabolic advantages.
Objective: The objective was to evaluate the effects of a diet with a high ratio of protein to carbohydrate during weight loss on body composition, cardiovascular disease risk, nutritional status, and markers of bone turnover and renal function in overweight women.
Design: The subjects were randomly assigned to 1 of 2 isocaloric 5600-kJ dietary interventions for 12 wk according to a parallel design: a high-protein (HP) or a high-carbohydrate (HC) diet.
Results: One hundred women with a mean (+/-SD) body mass index (in kg/m(2)) of 32 +/- 6 and age of 49 +/- 9 y completed the study. Weight loss was 7.3 +/- 0.3 kg with both diets. Subjects with high serum triacylglycerol (>1.5 mmol/L) lost more fat mass with the HP than with the HC diet (x +/- SEM: 6.4 +/- 0.7 and 3.4 +/- 0.7 kg, respectively; P = 0.035) and had a greater decrease in triacylglycerol concentrations with the HP (-0.59 +/- 0.19 mmol/L) than with the HC (-0.03 +/- 0.04 mmol/L) diet (P = 0.023 for diet x triacylglycerol interaction). Triacylglycerol concentrations decreased more with the HP (0.30 +/- 0.10 mmol/L) than with the HC (0.10 +/- 0.06 mmol/L) diet (P = 0.007). Fasting LDL-cholesterol, HDL-cholesterol, glucose, insulin, free fatty acid, and C-reactive protein concentrations decreased with weight loss. Serum vitamin B-12 increased 9% with the HP diet and decreased 13% with the HC diet (P < 0.0001 between diets). Folate and vitamin B-6 increased with both diets; homocysteine did not change significantly. Bone turnover markers increased 8-12% and calcium excretion decreased by 0.8 mmol/d (P < 0.01). Creatinine clearance decreased from 82 +/- 3.3 to 75 +/- 3.0 mL/min (P = 0.002).
Conclusion: An energy-restricted, high-protein, low-fat diet provides nutritional and metabolic benefits that are equal to and sometimes greater than those observed with a high-carbohydrate diet.