Genetics

There are several hundred genes associated with the tendency to put on weight, of which the FTO and MC4 genes are those most studied. The weights of identical twins are more similar than non-identical twins. A related approach is to look at adopted children and to see to what extent the child resembles the biological rather than adoptive parent. The association between the BMI of the child when adult, and the biological parents with whom they have not lived, is greater than with adoptive parents. However, given the slow rate at which the gene pool changes, and the rapid increase in obesity in the last 50 years, it is reasonable to see the increase in obesity as reflecting marked changes in the environment.