Having carried out organic farming research for three years prior to joining CABI, my attention is always grabbed by comparisons between organic and ‘conventional’ agriculture. The size of the organic food market continues to grow (the global organic food and drink market was projected to generate revenues of US$40 bn in 2006, according to British consultancy Organic Monitor), but the question of whether or not organic food is actually healthier for the consumer is one that continues to be controversial.
A ten-year study on organic tomatoes published in the Journal of Agricultural and Food Chemistry, which finds that organic tomatoes have almost double the level of flavonoids, has received widespread publicity this week, and will be used by the proponents of organic farming to support their argument for the health benefits of this type of agriculture. But Lord Krebs, former chairman of the UK’s Food Standards Agency (FSA) and long-standing organic sceptic, is not convinced, and a review published in the latest issue of the Nutrition Bulletin (Is organic food better for our health? Nutrition Bulletin 32 (2), 104–108) by Claire Williamson from the British Nutrition Foundation concludes that there is currently not enough evidence to recommend organic over conventionally produced foods.
The study on tomatoes (see here for the abstract) by Dr Alyson Mitchell from the University of California and collegues measured the amount of two flavonoids – quercetin and kaempferol – in dried tomato samples that had been collected as part of a long-term study on agricultural methods. They found that on average they were 79% and 97% higher respectively in the organic tomatoes than in the conventionally grown fruit – probably due to lower levels of nitrogen available to plants in the organic system, as flavonoids are produced as a defence mechanism that can be triggered by nutrient deficiency.
There is some evidence that flavonoids can help to reduce the risk of cardiovascular disease, and they have also been linked with reduced rates of some types of cancer and dementia.
But the evidence for health benefits from flavonoids is conflicting, and John Krebs says that even if there are benefits, higher flavonoid levels do not necessarily make organic food healthier. "This depends on the relevance of the differences to the human body," he says in New Scientist magazine. "Tomato ketchup has higher levels of lycopene than either organic or conventional tomatoes. So if you wanted lots of lycopene you should eat ketchup."
Each claim of health benefits from organic food brings a robust response from the critics. A number of studies (e.g. Ellis KA, Innocent G, Grove-White D et al. (2006) Comparing the fatty acid composition of organic and conventional milk. Journal of Dairy Science 89: 1938–50) have found that organic milk has a higher proportion of polyunsaturated fatty acids (PUFAs) to monounsaturated fatty acids in the organically produced milk, particularly the n-3 fatty acid ALNA (which is considered beneficial). But the FSA responded that the short-chain fatty acids found in milk do not have the same benefits as given by long-chain omega-3 oils found in oily fish, and Dr Anne Nugent of the British Nutrition Foundation said that " even if regular milk is slightly lower in these nutrients than organic milk, chances are you will be already be meeting your dietary needs for these nutrients by consuming other foods."
Whether in claims for food quality or benefits for the environment, it seems to be a common theme that comparisons between organic and ‘conventional’ agriculture (which of course covers a multitude of different farming practices) only ignite disagreement rather than lead to a consensus. Leading organic farming figures such as Lord Melchett of the Soil Association, who quickly welcomed the research by Alyson Mitchell and collegues, are always looking for evidence to boost the form of farming they support, while figures from the mainstream food and agriculture industries are keen to ensure that conventional produce is not regarded as inferior. Subscribers to CAB Abstracts (or to the internet sites nutritionandfoodsciences.org, or organic-research.com) can look at the research for themselves. Searching on the Cabicode QQ500 (food composition and quality) combined with the Subject Term ‘organic foods’ on nutritionandfoodsciences.org currently finds 195 bibliographic records, which can be narrowed down by adding the compound or product that interests you to the search string.