The effects of proteins and medium-chain fatty acids from milk on body composition, insulin sensitivity and blood pressure in abdominally obese adults

BACKGROUND/OBJECTIVES: To investigate whether intake of whey protein and butter naturally enriched in medium-chain fatty acids (MC-SFAs) (C6-C12) affected body composition, insulin sensitivity, blood pressure (BP) and plasma cholesterol concentrations. SUBJECTS/METHODS: A 12-week randomised, double-blinded, intervention study was completed in 52 abdominally obese adults. Subjects were assigned to one of four dietary supplementations: 63 g per day of milk fat with either high-( 8.5 g per day) or low-MCSFA (6.9 g per day) content combined with 60 g per day of whey or casein. We examined changes in the body composition by dualenergy X-ray absorption scan, insulin sensitivity using homoeostatic model assessment of insulin resistance (HOMA-IR) and Matsuda index, and diurnal BP and plasma cholesterol concentrations. Two-factor analysis of variance was used to examine the impact of MC-SFA content and protein type. RESULTS: We observed that lean body mass increased by 981 g (95% confidence interval (CI): 248-1713; P=0.010) after high-MCSFA compared with low- MC-SFA supplementation. Concomitantly, total body-fat percentage increased by 0.70 percentage points ( 95% CI: 0.10-1.31; P=0.024) after intake of low- MC-SFA butter compared with intake of high- MC-SFA butter. Both changes were independent of protein type (P=0.96 and P=0.99, respectively). We found no difference in HOMA-IR, Matsuda index, diurnal BP or plasma cholesterol concentrations related to MC-SFA content or protein type. CONCLUSIONS: Enhanced intake of MC-SFA increased the lean body mass and caused a significantly lower total body-fat percentage compared with lower intake of MC-SFA. Consequently, the composition of dairy fat should be considered when evaluating the impact of dairy products on body composition.