Compared to the WHO 2006 growth standard, infants in some countries have excessive early weight gain. This could be attributed to the linear relationship between total energy intake and infancy weight gain. In this presentation, Prof Ong discussed systematic reviews associating rapid infancy weight gain with subsequent obesity, and the persisting effects of early postnatal rapid (‘catch-up’) weight gain. Early rapid weight gains and obesity in later years could also be attributed to early weaning (ie, the introduction of solids). Early age at weaning may be a parental response to larger infant size, rapid growth and weight gain, or even higher infant hunger signals. Severe early-onset obesity could also be caused by rare mutations that delineate the ‘central’ regulation of appetite and satiety. Affected children have extremely high and insatiable appetites from infancy. Recent findings indicate that, in infants with rapid weight gain, rapid gains in lean body mass does not necessarily prevent future obesity.