Protein intake induced an increase in exercise stimulated fat oxidation during stable body weight

BackgroundProtein-rich weight-loss diets spare fat-free mass at the cost of fat mass. The objective was to examine if there is a change in stimulated fat oxidation related to protein intake during stable body weight.MethodsSubjects' (BMI 22 ± 2 kg/m2, age 25 ± 8 years) maximal fat oxidation (Fatmax) was assessed during a graded bicycle test, before and after a 3-month dietary-intervention of 2 MJ/day supplements exchanged with 2 MJ/d of habitual energy intake. The parallel design consisted of protein-rich supplements in the protein group and an isocaloric combination of carbohydrate and fat supplements in the control group. Daily protein intake was determined according to 24-h urine nitrogen. Body composition was measured according to a 4-compartment model by a combination of underwater-weighing technique, deuterium-dilution technique and whole-body dual-energy X-ray absorptiometry (DXA).ResultsSubjects were weight stable and did not change their physical activity. The protein group (n = 12) increased protein intake (11 ± 14 g, P < 0.05) and had significantly higher daily protein intake vs. control (n = 4) (80 ± 21 vs.59 ± 11 g, P < 0.05). Fatmax increased significantly in the protein group (0.08 ± 0.08 g/min, P < 0.01). Fat-free mass increased independent of change in body weight (P < 0.01), and fat mass and fat percentage decreased (P < 0.05). Change in Fatmax was a function of change in protein intake (r = 0.623, P < 0.05), and not of changes in body composition or VO2max.ConclusionIncreased stimulated fat oxidation was related to increased protein intake.

Research Highlights
► Subjects were weight stable and did not change their physical activity
► The protein group increased daily protein intake significantly higher vs. control
► Fatmax increased significantly in the protein group
► Change in Fatmax was a function of change in protein intake
► Fat-free mass increased independent of change in body weight