Research is first to find wide-ranging differences between organic and conventional fruits, vegetables and cereals
The team, led by Prof Carlo Leifert at Newcastle University, 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."
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 appeared on several academic websites.
The results are based on an analysis of 343 peer-reviewed studies from around 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 say 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.
The researchers found much higher levels of cadmium, a toxic metal, in conventional crops. Pesticide residues were found on conventional crops four times more often than on organic food. The research was funded by the EU and an organic farming charity.
The research is certain to be criticised: 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.
Also, the higher levels of cadmium and pesticides in conventional produce were still well below regulatory limits. But the researchers say cadmium accumulates over time in the 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.
This was also the conclusion of earlier, smaller studies published in 2009 in a scientific journal and by the UK Food Standards Agency (pdf), though the latter considered just 11 studies. The 2012 study did note that eating organic food might help people avoid pesticide residues.
Sanders said 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."
No Health Benefits from Organic Food
A recent review of 240 studies has concluded that:
The published literature lacks strong evidence that organic foods are significantly more nutritious than conventional foods. Consumption of organic foods may reduce exposure to pesticide residues and antibiotic-resistant bacteria.Organic produce has become increasingly popular in recent years. There are several reasons that consumers might prefer organic produce, including the belief that organic farming is better for the environment and more sustainable. I am going to focus in this article about the health effects of organic produce. Environmental claims for organic farming are complex and controversial – I will just say that such claims largely fall prey to the naturalistic and false dichotomy fallacies. In my opinion, farming practices should be evaluated on their own merits individually, based on evidence rather than philosophy. Sustainable and environmentally friendly farming are certainly laudable goals and I support farming practices promote them, however they are labeled.
The alleged superiority of organically grown produce is a separate question. In a 2003 survey 68.9% of people who purchase organic food said they did so because they believed it to be healthier (more than any other reason given). However, fifty years of research has so far not produced convincing evidence that there is any health benefit to consuming organic food. Likewise, systematic reviews of nutritional quality of organic produce also reveals no difference from conventional produce.
The recent review is therefore in agreement with previous reviews – organic produce is not more nutritious or healthful, but it is more expensive.
Some studies that find small differences in the content of specific nutrients may be due to confounding factors. For example, organic produce is generally smaller than conventional produce, so if nutrient content is measured by mass (as opposed to the total for an individual vegetable or piece of fruit) organic produce may have a slightly higher concentration. This does not necessarily translate to more overall nutrients for the consumer. Further, many studies measure multiple endpoints (nutrients) and find some differences, but may not be properly accounting for multiple analyses. The researchers in the recent study found that results were “heterogeneous” – meaning that there were significant differences in outcome among the studies. This could indicate a lack of replicability of specific outcomes, indicating that differences were more artifacts of method rather than genuine.
One type of study that I have not seen is essentially the equivalent of an “intention to treat” analysis – what is the impact of buying organic food in the real world. Even if there are tiny nutritional advantages to organic food (although to be clear this conclusion is not supported by the evidence), is there an overall nutritional advantage to eating organic? Does the higher price mean that for many consumers fewer overall fresh produce will be consumed?
The recent review did find that organic produce had fewer pesticide residues than conventional farming. However, there is no evidence that these low levels of pesticides present any health risk. The review found:
The risk for contamination with detectable pesticide residues was lower among organic than conventional produce (risk difference, 30% [CI, −37% to −23%]), but differences in risk for exceeding maximum allowed limits were small.So while there was a difference, this did not result in a significant difference in terms of exceeding safe limits. Further, studies looking at health outcomes did not find any significant difference between consuming organic vs conventional produce. These studies are limited in number and duration, however. Further, there may be a bias in how these studies are performed. Organic farming does use pesticides, but only “natural” pesticides are allowed. There is little to no evidence that these organic pesticides are less harmful for consumers or the environment. It is just assumed that they are based upon the naturalistic fallacy.
Even if we take the most pro-organic assumption – that there are more pesticides on conventional produce and that those pesticides have greater negative health effects than organic pesticides, it must still be recognized that simply washing fruits and vegetables effectively reduces pesticide residue. If minimized exposure to pesticide residue is your goal, thoroughly washing your produce is probably the easiest and cheapest way to achieve that end.
Differences in bacterial contamination were similar. There were no differences seen in E. coli contamination. There was a 33% greater chance of isolated a multi-antibiotic resistance bacteria on conventional produce, but no evidence this translates into a health risk. Again – even if we assume a difference in health risk (something not demonstrated by the data) this can be remedied by thorough washing.
Conclusion
The recent review of organic vs conventional produce agrees with previous systematic reviews that there is insufficient evidence to conclude that organic produce is healthier or more nutritious that conventional produce. Despite the scientific evidence, the alleged health benefits of organic produce is the number one reason given by consumers for buying organic. This likely represents the triumph of marketing over scientific reality.
