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.
Two years ago, the American Educational Research Association reported results
of a preliminary regression analysis which demonstrated a negative relationship between 5th graders’ reported fast-food consumption patterns and their reading and math test scores. Possible policy implications and directions for further research are discussed.
Kerri Tobin, of Vanderbilt University in Tennessee, studied the impact of a fast-food diet on the schoolwork of more than 5,500 10 and 11-year-olds. She found that those who ate higher-than-average amounts of junk food scored significantly lower than their classmates in a range of academic tests.
But Dr Tobin decided to test whether eating habits out of school also had a significant impact on pupils’ achievement. She therefore asked 5,500 primary pupils to record how many times a week they ate at fast-food restaurants such as McDonald’s or Wendy’s.
A total of 54 per cent had eaten fast food between one and three times during the previous week; 10 per cent had snacked on it between four and six times; and 2 per cent - or more than 110 pupils - said they ate four or more times daily.
Dr Tobin found no correlation between pupils’ fast food consumption and their weight, or between their parents’ income and the amount of fast food they ate.
But there was a direct correlation between how much junk food they ate and their scores in a series of literacy and numeracy tests.
Once other factors were taken into account, pupils who ate fast food between four and six times in a week scored 6.96 points below average in reading. Those who ate it daily dropped 16.07 points below average. And pupils who indulged three times a day dropped 19.34 points for reading.
A similar trend was noted in maths. Those eating fast food between four and six times a week scored 6.55 points below average. Daily junk-food led to a 14.82-point drop, and a three-a-day habit resulted in an 18.48-point drop.
Overall, higher-than-average consumption of fast food resulted in lower- than-average test scores: 12.79 points less for reading and 12.35 points for numeracy.
Dr Tobin suggests a number of explanations. “It is possible that the types of food served at fast-food restaurants cause cognitive difficulties that result in lower test scores,” she said.
The most current project at Bristol University is the first study to suggest a direct link between the diet of young children and their brainpower in later life. It 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.
The findings are the latest to be published from a major investigation of childhood development called the Avon Longitudinal Study of Parents and Children.
This tracks the long-term health and well-being of around 14,000 children born in the early 1990s.
Parents completed questionnaires about the food and drink consumed by their children at the ages of three, four, seven and eight.
Three dietary patterns were identified; a processed diet high in fats and sugar, a traditional diet of meat and vegetables and a health-conscious diet high in salad, fruit and vegetables.
Researchers Dr Pauline Emmett and Dr Kate Northstone said the effect of a poor diet on brain development could persist forever, even if the diet improved.
In the study published in the Journal of Epidemiology and Community Health, children’s IQ was measured when they reached eight years old.
Dr Emmett said that the diet for children aged four or seven years had no impact on IQ scores.
But the 20 per cent of children with the worst diet at the age of three had on average an IQ score five points lower than the group eating the best diet by the time they got to eight, she said.
She added: ‘The brain grows at its fastest rate during the first three years and good nutrition during this period may encourage optimal brain growth.
‘By the age of three, brain development is slowing down which is perhaps why the diet doesn’t have much effect afterwards.’
Dr Emmett said the ‘traditional’ diet of meat and vegetables and the health-conscious diet led to better IQ scores probably because they had more fresh fruit, vegetables, meat, fish and home-cooked foods.
‘This doesn’t mean you should never give your child a fizzy drink, chips or pizza, but these foods and drinks shouldn’t dominate the diet,’ she said.
‘Young children should be eating a normal family diet, with home-prepared fresh foods, but the problem is we have lost touch with food. People are frightened of preparing it from scratch.’
Dr Emmett, who has dietician training, said she admired TV chef Jamie Oliver’s attempts to get families cooking and eating together, using simple recipes and good ingredients.
The study of 4,000 children used a points system to score their diets. For every one point increase in scoring from a processed diet at the age of three, there was a 1.67 point fall in IQ points.
For those children who ate the other diets, every one point increase in the dietary pattern linked to a 1.2 increase in IQ.
Michael Nelson, director of research at The School Food Trust, which aims to improve the quality of food in schools, said: ‘Given that around 23 per cent of children start school overweight or obese, it’s clear that healthy choices as part of their early development will stand children in good stead – not only for keeping a healthy weight as they grow up, but as this evidence suggests, improving their ability to do well at school.’.