Demand for fish, vegetables and other "brain foods" has risen sharply as students look for ways of improving their exam revision.
Fish is believed to have qualities which aid mental powers
Supermarket Tesco found sales of tuna, cod, plaice and mackerel were up 34% in recent weeks in towns with large universities and colleges.
Broccoli, asparagus, spinach and vitamin supplements also grew in popularity.
Tesco's fresh produce director, Steve Murrells, said: "There's a growing belief that exam success can, quite literally, be served up on a plate.
"Students now prepare for their studying in the same way that athletes prepare for their races.
"For the first time, they are now using a good diet as well as intensive study to help boost performance during this critical time in their academic lives."
The supermarket found the trend towards healthier eating had been taking place in university towns and cities for the last two years.
Researchers believe it has now spread to A-level and GCSE candidates.
Other "brain foods" selling strongly include avocados, bananas, sprouts, lettuce, peanut butter and melons.
The increase in sales of fish was largest in university towns such as Cambridge, Oxford, Newcastle, Edinburgh and Durham.
York, Liverpool, Southampton, and Exeter showed similar rises.
Fish contains the nutrient dimethlyamino-ethanol, which is thought to improve the memory.