Many human and animal studies have shown that nutrition in early life can influence, in adulthood, such things as body fatness, blood lipids, blood pressure, atherosclerosis, behavior, learning and longevity.
Most other ways to estimate body fatness, such as by skin folds, body girths, body impedance and body scanners are based on equations which predict body density, and are inaccurate.
Such drift may have started because around 2 million years ago ancestral humans effectively removed the risk from predators, which was probably a key factor selecting against fatness.