The study in the Journal of Epidemiology and Community Health suggests a link between a diet high in processed foods and a slightly lower IQ.
The eating habits of 3,966 children taking part in the The Avon Longitudinal Study of Parents and Children were recorded at the ages of three, four, seven and eight and a half.
The researchers said three types of diet emerged: Processed diets which were high in fat, sugar and convenience foods, traditional diets of meat, potato and vegetables, and health conscious diets of salads, fruit and fish.
The children all took IQ tests when they were eight and a half and researchers found a link between IQ and diet, even after taking into account other factors such as the mother’s level of education, social class and duration of breast feeding.
A diet high in processed food at the age of three was linked to a slightly lower IQ at the age of eight and a half, suggesting early eating habits have a long term impact.
Dr Pauline Emmett, who carried out the study at Bristol University, said: “Brain development is much faster in early life as it’s when it does most of its growing. It seems that what happens afterwards is less important.”
Although the relationship between diet and IQ was very strong, the impact was quite small. Processed foods were linked with IQs only a few points lower.