Parents have provided a major boost to the market in nuts and seeds – but can they really get results?

It is the nutritional equivalent of sending your children to a crammer – stuffing them full of nuts and seeds in the run-up to exams in the vain hope of boosting their brain power. While it might sound a little like the last-ditch efforts of the desperate pushy parent, soaring sales figures of foods believed to improve cognitive function over recent weeks suggest that those parents are willing to part with their cash, despite the lack of scientific backing for the trend.

Research by Mintel suggests the growing market for all health foods in the UK is gaining impetus from parents determined to feed their families well, despite the economic downturn. The report found that while consumer spending has slowed generally, sales of healthy snacks are up by 14 per cent, with crisps and snacks down by 24 per cent.

"In the last month, sales of all our foods billed as 'brain foods' are up massively. Sales of walnuts have increased 23 per cent, linseed by 15 per cent and sunflower seeds by 19 per cent," said Alison Miles of the natural-food stockists Julian Graves. Similarly, the national chain saw huge increases in sales of dried fruit – long marketed as a good "school" snack – with 65 per cent more dates purchased, and figs and prunes flying off the shelves, too.

Many believe that this surge in popularity can be linked to health-food gurus such as Gillian McKeith (right), whose book You Are What You Eat was the most borrowed non-fiction book in UK libraries last year.

"There has been an increase in parents coming to us after seeing the Gillian McKeith programme. They are becoming more aware that what they feed their kids can seriously affect their brain power," said Deborah Colson, nutritional therapist at the Brain Bio Centre, part of the charity Food for the Brain.

But can foods such as nuts, seeds, oily fish and fruit really help to raise IQ and improve memory and concentration? With the prices of staples rising, some people question if it is necessary to buy special foods for children in the exam season.

"There is no good science to prove specific links between these foods and cognitive function," said Lisa Miles, senior nutrition scientist at the British Nutrition Foundation. "Admittedly, dried fruits are a good source of iron, and evidence does suggest that a high iron intake can help brain function, while a low intake can impair it. But the most important thing you can do... at exam time is to have regular eating patterns and to stay hydrated," she said.

But many doctors and nutrition experts agree that the consumption of essential fats found in nuts, seeds and oily fish can improve brain function. Patrick Holford, in his book Optimum Nutrition for Your Child's Mind, emphasises the importance of the fats.

Ms Colson said: "Sixty per cent of the brain is made up of essential fats, which the body cannot make; the only way of replacing them is through nuts and oily fish. There have been studies where schools have given fish oils to children and seen an improvement in their performance."

There seems to be little conclusive evidence as to whether or not eating these foods in the short term would have any effect on exam performance, however.

"It's a bit like going on a bikini diet six weeks before you go on holiday," Ms Colson said.

"You know that you should watch what you eat all year round, but you don't. While it would be more sensible to eat these foods all year, eating them in the weeks leading up to exams would still be worthwhile."