Journal Title (Medline/Pubmed accepted abbreviation): Med. Sci. Sports Exerc.
Page numbers: 249-254
doi (if applicable): 10.3945/jn.110.128520
Summary of Background and Research Design
Background:Reduction of excess body weight decreases one of the major risk factors for coronary heart disease. Several studies have reported that a dietary intake with higher protein and lower carbohydrate content promotes loss of body fat without loss of lean body mass. Branched-chain amino acids (BCAA) are involved in protein synthesis, and a few studies have shown weight and fat loss benefits with BCAA supplementation.
Hypothesis/purpose of study: The International Study of Macro-Micronutrients and Blood Pressure (INTERMAP) examined the association between BCAA intake and risk of being overweight/obese among multi-ethnic populations.
Subjects:The study evaluated 4,429 men and women 40 to 59 years of age from 17 diverse population samples; Japan (4 samples; n = 1,106), People’s Republic of China (3 samples; n = 822), United Kingdom (2 samples; n = 492), and United States (8 samples; n = 2,009).
Experimental design:Cross-sectional epidemiologic study
Treatments and protocol:Participants were interviewed 4 times; twice on consecutive days and twice again 3 weeks later. Dietary data on all foods, beverages, and supplements were collected at each interview. Nutrient intake for each participant was calculated using standardized tables for each country and expressed as energy density (% energy). Data were also collected for demographics and other cofounders. Timed 24 hour urine specimens were analyzed following Visit 2 and before Visit 3 for sodium, potassium, calcium, and urea nitrogen (protein intake index). Body mass index (BMI) was calculated at Visits 1 and 3. Overweight was defined as a BMI of 25 to 29 kg/m2, and obese was defined as ≥ 30 kg/m2. Data were analyzed by BCAA quartiles.
Summary of research findings:
- Overweight status ranged from approximately 25% in China to 70% in the US (approximately 26% in Japan and 69% in UK).
- Obesity followed a similar trend (1.9% in China, 3.4% in Japan, 22.4% in UK, and 33.3% in US).
- Overall mean BCAA intake was 2.6% energy.
- BCAA intake for China (2.1%) was significantly lower than for the other 3 countries, which were similar to each other.
- Compared with participants in the lowest BCAA quartile, participants in the highest quartile were
- More likely to be male
- Less likely to be smoking
- Taking in higher total protein, animal protein, and fat
- Taking in lower carbohydrates, starch, and total energy
- In multivariate-adjusted analyses comparing highest to lowest BCAA quartiles, BCAA intake was inversely related to overweight status (odds ratio = 0.70; P < .01) and obesity (UK and US analyzed; odds ratio = 0.75; P = .03).
- Adjusted for age, sex, country, employment status, physical activity, smoking status, special diet, and dietary intakes of energy, carbohydrate, fat, and protein.
- In data analyzed for US alone, the obesity relationship became nonsignificant (P = .12).
Interpretation of findings/Key practice applications:
In this study, low BCAA intake was associated with a higher prevalence of being overweight in the healthy middle-aged population of all countries evaluated. Low BCAA intake was also associated with a higher prevalence of obesity in the 2 Western countries evaluated. The results suggest that the reported weight loss from high-protein diets may be, in part, from BCAA intake. These results are consistent with those reported from animal studies and the few clinical studies available. One key limitation of this study is that it is a cross-sectional observational study, so cause and effect cannot be determined. It is also not clear whether this study was driven by a pre-existing hypothesis that BCAA intake would affect body weight or whether the hypothesis was developed after the data were collected. If the latter is true, the potential presence of a spurious statistical association cannot be ruled out. In support of this possibility, the overall rates of obesity and overweight varied dramatically from one country to the next, while the mean intakes of BCAA, both on percentage of energy (2.1% to 2.6%) and percentage of overall protein intake (~16% to 18% across the 4 quartiles) were relatively similar and tightly spaced across quartiles.