Causal link between milk consumption and obesity? A 10-year longitudinal study and a mendelian randomization study

Background: Obesity control and prevention remains challenging. Randomized controlled trials in western countries have demonstrated efficacy of dairy supplementation on fat mass reduction and lean mass increase, when combined with energy restriction protocols. However, there is scanty information on this issue among the East Asian population. Objective: The aim of this study is to investigate the association between milk consumption and weight status in Asian. Design: First, we studied the association between milk intake and body mass index (BMI) changes in a 10-year longitudinal study of Cardiovascular Disease Risk Factor Two-township Study (CVDFACTS) with 1,644 adults. Second, taking advantage of the genetic and phenotype data of 10,000 participants collected by Taiwan Biobank (TWB), we carried out a Mendelian randomization (MR) study to investigate the causal relationship between milk intake and BMI. A lactase persistence genetic marker (rs4954490) was used as the instrumental variable. Results: We found in the longitudinal study that higher baseline milk consumption level was associated with lower odds of increasing BMI or maintaining overweight/obesity status. In the MR study, we found that G allele of the rs4954490, a surrogate of greater milk intake, was associated with lower odds of being obese (BMI > 27 kg/m²); the odds ratio (OR) for the GG versus AA is 0.85 (P = 0.037), and the OR for the GA versus AA is 0.84 (P = 0.032). Conclusions: These findings support current food guide in Asian countries to include dairy group as one of the six food groups for nutrition recommendation.