Changes in body fat percentage during body weight stable conditions of increased daily protein intake vs. control.

Objective: The objective of this study was to examine if increased protein intake vs. control influences body fat percentage during stable body weight.

Design: Body composition was assessed before and after a 3-month isoenergetic dietary intervention of 2MJ/d supplements exchanged with 2MJ/d of habitual ad libitum energy intake. The parallel design consisted of protein-rich supplements in the protein group (n=12) and an isoenergetic combination of carbohydrate and fat supplements in the control group (n=12). Daily protein intake was calculated from a 24h urinary nitrogen. Body composition was measured by a combination of underwater-weighing technique, deuterium-dilution technique and whole-body dual-energy X-ray absorptiometry (DXA), a method that allows for estimation of 4-body compartments (fat and lean; water, bone and rest).

Results: Subjects were weight stable and did not change their habitual physical activity. Daily protein intake increased in the protein group during the intervention compared to baseline with +11±14g (P<0.05) vs. the control group that did not change their protein intake -1±15g. This resulted in a significant difference in protein intake during the intervention of 80±21g of the protein group vs. 59±11g of the control group (P<0.01). Change in body fat percentage showed a significant group×time interaction of decreased body fat percentage of -1.0±1.1% of the protein group vs. 0.1±0.6% of the control group (P<0.05). The group×time interaction of change in fat mass was significant (P<0.05), and change in fat-free mass was a trend (P=0.05). Fat-free mass of the protein group had increased with +0.9±0.6kg (P<0.01), and fat mass had decreased with -0.6±0.8kg (P<0.05), while the control group had not changed.

Conclusion: During increased daily protein intake vs. control body fat percentage decreased with unchanged physical activity during 3months of stable body weight.