Toddlers fed a diet of junk food can suffer lasting damage to their brainpower, researchers warn.
Children who eat more chips, crisps, biscuits and pizza before the age of three have a lower IQ five years later, a study showed.
The difference could be as much as five IQ points compared with children given healthier diets with fruit, vegetables and home-cooked food.
But even if their diet improves, it could be too late as the ill-effects can persist for a lifetime.
This is the first study to suggest a direct link between the diet of young children and their brainpower in later life.
The project at Bristol University took account of factors such as social class, breastfeeding and maternal education and age.
Researchers also allowed for the influence of the home environment, for example a child's access to toys and books.
They said good nutrition was crucial in the first three years of life when the brain grows at its fastest rate.
Young children eating a diet packed with fats, sugar and processed foods consume too few vitamins and nutrients, which means their brains never grow to optimal levels.