Meta-analysis of lactase phenotypes on obesity, metabolic syndrome and milk consumption

Background The variability in lactose digestion ability is categorised into lactase persistence and lactase non-persistence phenotypes, primarily determined by the 13 910 C>T single nucleotide polymorphism (rs4988235). The relationship between the lactase gene, obesity and milk consumption has been studied, but the result remains discrepant. We aimed to investigate the association between lactase phonotypes/genotypes and obesity while also exploring potential connections with metabolic syndrome and milk consumption. Objective To investigate the association between lactase phenotypes/genotypes and 1) body mass index, 2) obesity/overweight status, 3) metabolic syndrome and 4) milk consumption. Methods A systematic literature search of Medline (via PubMed search engine) and Scopus databases was conducted up to August 2023. Data extraction was performed independently by three investigators. Meta-analysis utilised fixed and random effects, with heterogeneity assessed using Higgin’s I² statistic. Publication bias was examined using funnel plots. Results Twenty-six studies were included (5 in children, 21 in adults). In children, body mass index did not significantly differ based on the lactase phenotypes (mean difference 0.17 kg/m², 95% CI −0.26 to 0.60; p=0.44 (three studies)). However, among adults, lactase persistence individuals had a higher body mass index (mean difference 0.22 kg/m², 95% CI 0.15 to 0.30; p<0.01 (19 studies)) and an increased risk of obesity/overweight by 27% (OR 1.27, 95% CI 1.07 to 1.52; p=0.01 (four studies)) as compared with the lactase non-persistence. Even though it was not associated with metabolic syndrome (OR 0.98, 95% CI 0.61 to 1.57; p=0.93 [three studies]), lactase persistence was associated with higher milk consumption (mean difference of 41 g/day, 95% CI 26 to 56, p<0.01 [six studies]). Conclusions While data on lactase phenotype and obesity in children are limited, adults with lactase persistence have higher body mass index and risk of obesity/overweight and greater milk consumption than lactase non-persistence. More research is needed to define the interplay between lactase genotypes/phenotypes, obesity and milk consumption. PROSPERO registration number CRD42023400753.