The objective was to review whether nutrition during pregnancy and the first 3 y of life predisposes individuals to be fatter as adults. The roles of undernutrition, overnutrition and breastfeeding were considered. The evidence that poor nutrition in early life is a risk factor for increased fatness later in life is inconclusive. Overnutrition, as proxied by high birthweight or gestational diabetes, on the other hand, is associated with subsequent fatness. Two large, well-conducted studies in developed countries suggest that breastfeeding has a protective effect. Nutrition in early life has a demonstrable but small impact on adult obesity.