Excess body fat is a critical public health problem with an increasing frequency worldwide. To develop strategies for prevention it is important to identify predisposing factors related to nutrition. A previous study has suggested that a high fat intake in infancy is related to a lower body fat and lower serum leptin concentrations at age 20 years, suggesting that early low fat intake could increase the susceptibility to development of overweight and leptin resistance at later ages. This is known as early fat programming. Studies in rats are in line with these finding in humans. The relationship between dietary factors and adiposity may be modified by child sex since there is a difference in some circulating hormones that is present from an early age. This hypothesis needs to be tested in a larger cohort where males and females can be assessed separately.