Three boys and one girl, aged between eight and 13, who were overweight took part in the tests designed to look at the effects of junk food on young brains.
They were asked to be more active and cut down on unhealthy snacks and fizzy drinks.
At the same time, they were given two capsules a day of the VegEPA supplement, which contains an omega-3 fatty acid called EPA.
Tests done at the end of the three-month study found the children showed an increase in reading age of well over a year, their handwriting became neater and more accurate and they paid more attention in class.
Brain scans which identified a chemical called N-Acetylaspartate (NAA) which is linked to the growth of nerve fibres in the brain also showed dramatic changes, said Professor Puri.
Although the children were encouraged to change their diet, there was no evidence they did this to any great extent, suggesting the improvements in the children were a result of the supplement.