Organic apples and pears. Photograph: David Sillitoe for the Guardian
Organic food has more of the antioxidant compounds linked to better health and lower levels of toxic metals and pesticides, according to the most comprehensive scientific analysis to date.
The international scientific team behind the new work suggests that switching from regular to organic fruit and vegetables could give the same benefits as adding one or two portions of the "five a day" currently recommended.
The team, led by Prof Carlo Leifert at the University of Newcastle, concludes that there are "statistically significant, meaningful" differences, with a range of antioxidants being "substantially higher" – between 19% and 69% – in organic food. It is the first study to demonstrate clear and wide-ranging differences between organic and conventional fruits, vegetables and cereals.
The researchers say the increased levels of antioxidants are equivalent to "one to two of the five portions of fruits and vegetables recommended to be consumed daily and would therefore be significant and meaningful in terms of human nutrition, if information linking these [compounds] to the health benefits associated with increased fruit, vegetable and whole grain consumption is confirmed".
The findings will bring to the boil a long-simmering row over whether those differences mean organic food is better for people, with one expert calling the work sexed up.
Tom Sanders, a professor of nutrition at King's College London, said the research did show some differences. "But the question is are they within natural variation? And are they nutritionally relevant? I am not convinced."
He said Leifert's work had caused controversy in the past. "Leifert has had a lot of aggro with a lot of people. He is oversexing [this report] a bit." Sanders also noted that the research showed organic cereals have less protein than conventional crops.
The research was peer-reviewed and is published in a respected scientific journal, the British Journal of Nutrition. It was due to be released next week, but has already appeared on severalacademicwebsites.
The results are based on an analysis of 343 previous peer-reviewed studies from all over the world – more than ever before - which examine differences between organic and conventional fruit, vegetables and cereals.
"The crucially important thing about this research is that it shatters the myth that how we farm does not affect the quality of the food we eat," said Helen Browning, chief executive of Soil Association, which campaigns for organic farming.
UK sales of organic food, which is often considerably more expensive than non-organic, are recovering after a slump during the economic crisis.
Plants produce many of their antioxidant compounds to fight back against pest attacks, so the higher levels in organic crops may result from their lack of protection by chemical sprays. But the scientists argue that other reasons may be important, such as organic varieties being bred for toughness and not being overfed with artificial fertilisers.
Leifert and his colleagues conclude that many antioxidants "have previously been linked to a reduced risk of chronic diseases, including cardiovascular diseases, neurodegenerative diseases and certain cancers". But they also note that no long-term studies showing health benefits from a broad organic diet have yet been conducted.
One of the most striking results from the work was the much higher levels of cadmium, a toxic metal, in conventional crops. They also found that pesticide residues were found on conventional crops four times more often than on organic food. The research was funded by the European Union and an organic farming charity.
The research is certain to be criticised for a number of reasons. The inclusion of so many studies in the analysis could mean poor-quality work skews the results, although the team did "sensitivity analyses" and found that excluding weaker work did not significantly change the outcome.
Another criticism is that the higher levels of cadmium and pesticides in conventional produce were still well below regulatory limits. But the researchers argue that cadmium accumulates over time in the human body and that some people may wish to avoid this, and that pesticide limits are set individually, not for the cocktail of chemicals used on crops.
A further criticism is that the differences seen may result from different climate, soil types and crop varieties, and not from organic farming, though the researchers argue that combining many studies should average out these other differences.
The greatest criticism, however, will be over the suggestions of potential health benefits. The most recent major analysis, which took in 223 studies in 2012, found little evidence. "The published literature lacks strong evidence that organic foods are significantly more nutritious than conventional foods," it found.
Sanders told the Guardian he was not persuaded by the new work. "You are not going to be better nourished if you eat organic food," he said. "What is most important is what you eat, not whether it's organic or conventional. It's whether you eat fruit and vegetables at all.
"People are buying into a lifestyle system. They get an assurance it is not being grown with chemicals and is not grown by big business."
He added that organic farming did help to address the significant problem in the UK of soil degradation and excess fertiliser polluting rivers.
Soil Association polling (pdf) shows healthy eating (55%) and avoiding chemical residues (53%) are key reasons cited by shoppers for buying organic produce. But many also say care for the environment (44%) and animal welfare (31%) are important, as is taste (35%).
Browning said: "This research backs up what people think about organic food. In other countries there has long been much higher levels of support and acceptance of the benefits of organic food and farming. We hope these findings will bring the UK in line with the rest of Europe."