Research carried out at Goldsmiths, University of London, identified a link between poor diet and lower IQ scores in children aged between three and five.
The study was based on a sample of 4,000 Scottish kids, with the researchers taking into account their socio-economic status when drawing up the results.
Interestingly, it was discovered that children from poor socio-economic backgrounds were typically fed more fast food.
In contrast, parents from higher socio-economic backgrounds were more inclined to give their kids a healthy diet.
More noteworthy, however, was the result that children fed a diet rich in fast food generally had lower intelligence than their healthy-eating peers.
Dr Sophie von Stumm, from the department of psychology at Goldsmiths, argued that it was common sense that the types of food we eat affect brain development.
She highlighted that previous research has only taken into account specific food groups when looking at children's diets.
"This research will go some way to providing hard evidence to support the various high-profile campaigns aimed at reducing the amount of fast food consumed by children in the UK," Dr van Stumm said.
According to the expert, parents from underprivileged backgrounds tend to have less time to prepare freshly cooked meals for their kids, with the lower IQ scores hindering their ability at school.
The findings coincide with the latest research from Canada, which revealed overweight and obese children are more likely to demand prescription medication than healthy weight kids.
More than 2,000 children aged between 12 and 19 were involved in the study that also established a link between being overweight or obese and suffering from respiratory problems like asthma and allergies.
According to the findings published in the Archives of Disease in Childhood, overweight and obese kids are 59 per cent more likely to take prescription medication than their normal weight peers.