Abstract
BACKGROUND: Childhood obesity has tripled in the past 40 years with nearly 1 in 3 children in Canada now overweight or obese. Over the same period, consumption of whole cow’s milk has halved. Health Canada recommends that children switch from whole fat cow’s milk (3.25%) to reduced fat cow’s milk (0.1 to 2%) at 2 years of age to limit fat intake and minimize the risk of childhood obesity. Given that cow’s milk is consumed daily by most children in Canada and is a major dietary source of energy, protein and fat, understanding the relationship between cow’s milk fat and risk of overweight or obesity is important. To our knowledge, no systematic review or meta-analysis has evaluated the relationship between cow’s milk fat consumption and childhood adiposity. OBJECTIVES: The primary objective of this study was to evaluate the relationship of whole fat (3.25%) compared to reduced fat (0.1 to 2%) cow’s milk and adiposity in children aged 1 to 18 years among existing literature. DESIGN/METHODS: A systematic review and meta-analysis was conducted. Data sources included EMBASE, CINAHL, Medline, SCOPUS, and Cochrane Library databases from inception to March 2018. Inclusion criteria were observational and interventional studies of healthy children aged 1–18 years which evaluated the association between cow’s milk fat consumption and child adiposity. Risk of bias and study quality was assessed using the Newcastle Ottawa Scale; methodological characteristics and results were summarized. A meta-analysis was conducted using a random effects model to evaluate the relationship between cow’s milk fat consumption and overall risk of childhood overweight or obesity. RESULTS: Inclusion criteria were met by 18 cross-sectional studies, 9 prospective cohort studies and no interventional studies. Overall, 16 of 27 studies found that higher cow’s milk fat was associated with lower adiposity, 1 study found that higher cow’s milk fat was associated with higher adiposity, and 10 studies did not identify an association. Meta-analysis using pooled data from 12 studies (N=20,171) with data on the proportion of children who consumed whole vs. reduced fat milk as well as direct measures of overweight or obesity identified that cow’s milk fat was associated with lower risk of childhood overweight or obesity (p<0.0001). Among children who consumed whole (3.25% fat) milk, the odds ratio for overweight or obesity was 0.62 (95% CI 0.52 to 0.73, I2 = 76.0%) compared with children who consumed reduced fat (0.1 to 2%) milk. CONCLUSION: Observational research findings on the risk of child overweight or obesity do not support current international guidelines which recommend transitioning from whole to reduced fat cow’s milk at age two years of age. While the underlying causal relationship may include reverse causality, randomized controlled trial data is needed to determine which milk fat content optimizes childhood growth.