A debate which will surely never be settled to everyone’s satisfaction is that about the supposed benefits of organic food and farming. This week, publication of another study has reignited the controversy: Study sparks organic foods debate, according to the BBC. Headlines vary – Clear differences between organic and non-organic food, study finds, says the Guardian, while the Independent reports the story as An unhealthy row: report claiming organic food is better divides UK scientists– but the crux of the argument is that levels of antioxidants are consistently higher and cadmium lower in organic food.
The study, entitled Higher antioxidant and lower cadmium concentrations and lower incidence of pesticide residues in organically grown crops: a systematic literature and meta-analyses, is to be published in the British Journal of Nutrition but the summary is available on the PubMed website. As the reports make clear, the study was part funded by an organic farming charity (the Sheepdrove Trust) but we should not be too quick to question its credibility on that basis alone.
The lead author, Carlo Leifert, professor of Ecological Agriculture at Newcastle University, is quoted in the Independent as saying “The organic versus non-organic debate has rumbled on for decades now but the evidence from this study is overwhelming – that organic food is high in antioxidants and lower in toxic metals and pesticides.” Not surprisingly, this was welcomed by the chief executive of the Soil Association, Helen Browning: "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."
Given that other recent literature reviews have failed to find such consistent differences, it is equally unsurprising that there has been criticism of the study from other scientists. Prof Tom Sanders of King’s College London (head of their Diabetes and Nutritional Science Division) told the BBC: "This article is misleading because it refers to antioxidants in plants as if they were a class of essential nutrients, which they are not. In terms of macronutrients (protein, carbohydrate, fat), the organic products contained less protein. Other nutrient differences were trivial and well inside the normal range of variation that occurs with different varieties, soil types and variations in weather. This study provides no evidence to change my views that there are no meaningful nutritional differences between conventional produced and organic crops."
The authors of the current study claim that their findings are due to the availability of a larger amount of evidence: 343 peer-reviewed studies are included in the survey. What is not certain is the quality of this evidence. The fact that all the studies were peer-reviewed does not give much comfort, since the peers involved may often themselves be sympathetic to the organic movement. In any case, the review process often does little more than sift out basic errors and the quality of publications varies widely.
In stark contrast, a 2009 FSA-sponsored review by Alan Dangour and colleagues from the Royal School of Hygiene and Tropical Medicine selected just 55 of 162 available studies, with the rest being deemed flawed. This resulted in headlines such as Organic ‘has no health benefits’.
There are two crucial differences between the Dangour and Leifert studies: the latest one finds greater compositional differences between organic and conventionally-produced food and it also implies that these would be beneficial for health. However, the quote from Prof Sanders sums up the criticism from nutritionists: the differences found were in low levels of compounds whose nutritional significance is not known. The higher level of cadmium found in non-organic food is still well within normal safety limits. Interestingly, the Broadbalk experiment run by Rothamsted Research, with plots of wheat receiving different fertilisation treatments since the mid-19th Century, shows a build-up of heavy metals in soil treated annually with animal manure, one of the main inputs used by organic farmers.
The other interesting point about the Leifert study is that the antioxidants which appear to be higher in organic food are in fact natural pesticides. There are no concerns expressed about these compounds, while the presence of traces of synthetic pesticide residues is regarded as cause for concern.
Underlying this is the philosophical belief that natural compounds are generally good, while synthetic ones are suspect. In fact, anything can be hazardous above a particular threshold and there are plenty of plants which are poisonous and should be avoided. Equally, pretty much everything is safe, or even beneficial, below a certain exposure level. The assumption that if something is toxic at one level all traces of it must be avoided is an easy one to make, but this and the belief that ‘natural’ means ‘good’ underpins the organic philosophy.
Like all beliefs, this is not something amenable to rational argument. Those who believe it will take this latest study as evidence to support their view, despite reasoned criticisms from expert nutritionists. And, of course, if people choose to buy organic food, there is absolutely no harm in that. However, what we need to steer clear of is official sanction for the unsupported belief that doing so is healthier.
Martin Livermore
The Scientific Alliance
St John’s Innovation Centre
Cowley Road
Cambridge CB4 0WS
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