Turkeys and chickens are grossly overweight ... don't panic, but what are you going to have for Christmas dinner? Read our food blog for a shellfish Christmas and share your plans

Forget the Christmas pudding, stuffing and mince pies - it's the turkey that really does the festive damage to your waistline, says a new report.

Far from being lean and healthy, white meat is full of the sort of fats that cause obesity and increase your chances of a heart attack, says a scientific study. Poultry products sold in supermarkets contain far higher levels of adipose fat than previously thought, a team of nutrition experts from London Metropolitan University has found.

Professor Michael Crawford, who headed the team, said: 'The public thinks of chickens as lean products and a much healthier alternative to red meat. But we found that typical supermarket chickens are very fatty.' The biochemist blamed the over-feeding and lack of exercise involved in the battery farming of chickens for altering the birds' natural physiological balance. Turkeys produced using similar methods would be as high in 'bad fat' as chickens, he added.

'People think that poultry is lean, but it is grossly fat,' said Crawford. 'When I bought a turkey several Christmases ago it was perfect; only a teaspoon of fat came out when it was cooked. But a year later the turkey for that Christmas was absolutely swimming in fat in the oven tray, even though it was supposedly a free-range bird.'

Crawford and three colleagues at the university's Institute of Brain Chemistry and Human Nutrition conducted tests on 52 batches of 14 different sorts of chicken products bought in high street supermarkets, such as legs, breast pieces and whole chickens. The results showed that the amount of fat contained within these birds has risen dramatically in the last 30 years.

They found that in 13 of the 14 categories, the amount of 'bad fats', known as triglycerides, now outweighed the amount of 'good fats', called phospholipids, which are useful for brain development, often by massive margins.

Nine of the 14 sorts of chicken tested were organic. But eight displayed the same unhealthy ratio of bad to good fat. 'That surprised us and will surprise consumers, who think that organic equals goodness,' said Crawford.

While red meat has been identified by a growing number of studies as a potential cause of cancer, white meat has appeared increasingly appealing as a supposedly healthy alternative. But the latest findings appear to pose a direct challenge to the FSA's existing nutrition advice, which states that those 'making healthier choices when buying meat' should ask their butcher for a lean cut and 'go for turkey and chicken, without the skin, because these are lower in fat'.

An FSA spokeswoman said: 'The agency keeps a watching brief on emerging evidence and we will certainly look at this report once it's published.'

· Turkeys and chickens are grossly overweight ... don't panic, but what are you going to have for Christmas dinner? Read our food blog for a shellfish Christmas and share your plans