Dairy foods are a rich source of dietary branched-chain amino acids (BCAA), essential for muscle protein synthesis and cellular signalling. However, emerging evidence suggests that chronically elevated fasting plasma BCAA concentrations in humans is associated with insulin resistance, and increased risk of type 2 diabetes (1) and can be influenced by dietary fat intake and composition (2) . Higher BCAA concentrations have also been observed in individuals with greater body mass index (BMI) (3) and in males compared to females (4) . However, much of the evidence is from cross-sectional studies and little is known about the effects of dietary BCAA intake on circulating concentrations. This secondary analysis of the RESET (REplacement of SaturatEd fat in dairy on Total cholesterol) study (5) aimed to determine whether increasing dairy intake and/or modification of the fatty acid (FA) composition of dairy products in the diet affects fasting plasma BCAA concentrations in adults at moderate cardiovascular disease (CVD) risk. The RESET study was a double-blind, randomised, controlled, cross-over trial that investigated the cardiometabolic effects of partially replacing saturated fatty acids (SFA) with monounsaturated fatty acids (MUFA) in dairy products using a food-chain approach. Fifty-four adults (mean ± SEM age: 52 ± 3 years; BMI: 25.8 ± 0.5 kg/m2; 57% male) consumed two isoenergetic, high-fat, high-dairy diets for 12 weeks each: control (19% total energy (TE) SFA, 11% TE MUFA) and modified (16% TE SFA, 14% TE MUFA), separated by an 8-week washout. Total fasting plasma BCAA concentrations (sum of leucine, isoleucine and valine) were quantified using NMR (Nightingale Health Ltd.) in samples collected at the beginning and end of each dairy intervention. A linear mixed model was used to assess the effects of diet, time (pre- vs post-intervention), and their interaction (diet x time) on fasting plasma BCAA, with adjustments for age, sex, intervention order and BMI category (normal weight: 18.5-24.9 kg/m2 compared to overweight/obese: ≥25 kg/m2). Associations with insulin and glucose concentrations were also explored. There was no significant effect of diet (p=0.267), time (p=0.758), diet x time interaction (p=0.268), insulin (p=0.504) or glucose (p=0.560) on total fasting plasma BCAA concentrations. Sex and BMI category, however, were significant determinants, independent of increased dairy intake or altered FA composition. Males had higher BCAA concentrations than females (p<0.001), and participants classified as overweight/obese had greater concentrations than those in the normal weight category (p=0.003). No effects of age or intervention order were observed. These findings suggest that longer-term increases in dairy intake or modification of dairy FA composition did not influence total fasting plasma BCAA concentrations in adults at moderate CVD risk. Instead, total fasting plasma BCAA were more strongly associated with inherent characteristics such as sex and BMI, in line with previous research.
Bell et al. (Fri,) studied this question.