Effects of protein vs. carbohydrate-rich diets on fuel utilisation in obese women during weight loss.

Background: Energy restriction is a common therapeutic approach for weight reduction, but the most effective macronutrient distribution of the hypoenergetic diet as well as the role of the metabolic processes involved require further investigations.

Objective: To study the effect of a high protein (HP) hypoenergetic diet compared with a high carbohydrate (HC) hypoenergetic diet on fuel utilisation changes during the weight loss process in obese women.

Design: Eleven obese (BMI>30) women were randomly assigned to a 10w dietary intervention study comparing HP (30% protein) or HC (55% carbohydrate) energy restricted diets providing 30% energy fat content. Substrate utilisation was evaluated by indirect calorimetry. Body weight and composition (Bod Pod) and blood measurements were performed before and after weight loss.

Results: On average, the individuals on the HP dietary group lost 4.4 kg more than those in the HC program (p<0.50), which was mainly due to a fat mass loss (3.7 kg, p<0.05) with no statistical differences in lean body mass reduction. These losses were accompanied by a significant decrease in fasting leptin in the HP group (-52%; P<0.05). On the other hand post-absorptive lipid oxidation decreased in the HC group (-48%) and remained unchanged in the HP groups.

Conclusions: The replacement of some dietary carbohydrate by protein in energy restricted diets, improves weight and fat losses and specifically promotes lipid oxidation in the fasting state, without major different in lean body mass depletion.