New evidence has emerged showing that organic food does contain nutrients that deliver health benefits, contrary to the view put forward earlier this year by David Miliband, who said it was only a "lifestyle choice".
Scientists in Britain, France and Poland examined organic carrots, apples, peaches and potatoes and discovered that they have greater concentrations of vitamin C and chemicals that protect against heart attacks and cancer than non-organic produce. The research could challenge official government guidelines which suggest there is no evidence of organic food being healthier than conventional produce. That led to the assertion by Mr Miliband, the Environment Secretary, which he later qualified by saying that he ate organic food both because of its taste and the environmental benefits.
The new studies found that organic tomatoes had more vitamin C, beta-carotene and flavonoids, which are known to help against cancer and heart disease, though they also had less lycopene, which is thought to help prevent skin ageing, diabetes and osteoporosis. Organic apple puree was found to contain more phenols, flavonoids and vitamin C than non-organic versions.
"This research shows there are benefits," said Dr Kirsten Brandt of Newcastle University, which led the research. "The reason why it's such a grey area is because it's extremely difficult to measure the health benefit in any food, but we can say that if you eat 400g of fruit and vegetables per day you would get 20 per cent more nutrients in organic food."
Peter Melchett, policy director of the Soil Association, welcomed the new research. He said: "There is clear evidence that a range of organic foods contain more beneficial nutrients and vitamins and less of things known to have a detrimental health effect."
The study follows US research published last week suggesting organic kiwi fruit has higher levels of nutrients than conventional crops. The kiwi fruit was found to have significantly more polyphenols - the healthy compounds found in red wine and coloured berries. It also had higher levels of antioxidants and vitamin C, according to a report published in the magazine Chemistry & Industry.
The French element of the latest study looked at organic peaches and found they had "a higher polyphenol content at harvest" and concluded that organic production had "positive effects ... on nutritional quality and taste". Researchers at Warsaw Agriculture University found similar benefits in organic tomatoes.
Dr Brandt's work on organic produce included a focus on a natural pesticide in carrots, falcarinol, which is believed to reduce cancer tumours. This led her to conclude two years ago that a raw carrot eaten each day might be better than the recommended five portions of fruit and vegetables.
Sales of organic food rose by 30 per cent last year to £1.6bn. But until now the health benefits of organic food have been the subject of conjecture. Last September, the Food Standards Agency refused to issue official guidance highlighting the benefits. It said that while it accepted higher levels of nutrients might exist they were of less value than long-chain fatty acids.
The debate intensified last month when a report for the Department for Environment, Food and Rural Affairs found "many" organic products had lower ecological impacts than conventional methods using fertilisers and pesticides.
But the study said other organic foods - such as milk, tomatoes and chicken were significantly less energy efficient and could be more polluting than intensively farmed equivalents.