There is increasing evidence that factors in early life are important for the risk of developing overweight and obesity later in childhood. Among the postnatal factors, breastfeeding and complementary feeding are especially interesting because the pattern of these two factors can be changed. Breastfeeding has been shown to reduce the risk of later obesity, although the effect is not substantial. Complementary feeding also seems to play a role. There is some evidence that a high protein intake is associated with a higher risk of obesity later in childhood, whereas a high fat intake during the complementary feeding period does not seem to be a risk factor for later obesity. Thus, the dietary pattern during this period is different from the pattern seen in older children and adults where a high fat intake is associated with a higher risk of obesity and a high protein intake in some studies seems to protect against obesity. A few studies have also suggested that early introduction of complementary foods (before age 4 months) is associated with an increased risk of later obesity. A high weight gain during early life, especially the first 6 months, is associated with a higher risk of developing obesity. However, some studies suggest that weight gain during the 6- to 12-month age period, when complementary feeding is introduced, is not associated with later obesity. Insulin-like growth factor-1 (IGF-1) values and body composition both play a role in the complex pattern between early diet and later obesity, but our present knowledge about how these factors are influenced by diet during infancy is limited. Future studies should include longitudinal data on IGF-1 and body composition during infancy to improve our understanding of how diet in early life can play a role in prevention of later obesity.