Genes, mating and fertility as determinants of global obesity trends

We use formal models to assess the effects of ancillary processes that drive the global obesity epidemic, genetic heritability, gene-environment interactions, assortative mating and fertility differentials. We address a central question in the literature on obesity, namely, whether assortative mating by body size is a key determinant of time trends of the obesity phenotype. We compare the effect of assortative mating and fertility differentials to that of gene variants and gene–environment interactions. We find that changes in assortative mating have only a small direct influence on obesity trends, though they moderate the effects of fertility differentials. Contrary to mainstream views, assortative mating is neither likely to have had a significant influence in the past nor to have one on future obesity trends. We show that the effects of genes and gene–environment interactions are more important than those of assortative mating but less so than those of fertility differentials.