The amount of omega-3 fatty acid DHA, a nutrient essential for a healthy human brain, has fallen dramatically in commercially-bred chickens, researchers at London’s Institute of Brain Chemistry and Human Nutrition have discovered.

In the last twenty years the amount of this key nutrient has dropped to 25 milligrams per 100 grams of chicken. In 1980 a typical chicken contained 170 milligrams of DHA per 100 grams.

Professor Michael Crawford, one of the authors of the report, said that the decline of omega-3 fatty acid in chicken meat was the result of the diet fed to commercially reared birds.

“Chickens used to roam free and eat herbs and seeds. They are now fed with high energy foods and even most organic chickens don’t have to walk any distance to eat,” said Professor Crawford.

Omega-3 fatty acid helps feed the brain, helping to prevent Alzheimer’s and heart disease. The best sources of this nutrient are oily fish such a salmon and sardines.

The report also said that the calorific value of chicken had increased. Modern birds now have three times the fat content than 35 years ago, again because their diet is aimed at fattening them up as quickly as possible.

Nutritionists recommend grilling chicken after removing the skin, where most of the fat is deposited in chicken.