Organic produce tends to carry a premium, but debate about whether it has nutritional advantages over conventional produce has raged recently. Studies on the matter have come down on both sides.
The new review, conducted at the London School of Hygiene and Tropical Medicine and funded by the UK’s Food Standards Agency, involved a systematic search of studies between 1958 and 29 February 2008. Of the 162 identified, 55 field trials, farm surveys and basket surveys deemed to be of “satisfactory quality” were included in the analysis.
The investigators looked at the levels of nitrogen, vitamin C, phenolic compounds, magnesium, calcium, phosphorous, potassium, zinc, total soluble solids, copper and titratable acidity.
With the exception of nitrogen (higher in conventional), phosphorous and tritratable acidity (both higher in organic), no differences were seen.
“One broad conclusion to draw from this review is that there is no evidence to support the selection of organically produced foodstuffs to increase the intake of specific nutrients or nutritionally relevant substances,” they wrote in the American Journal of Clinical Nutrition.
However they immediately added that research in this area sorely needs more scientific rigour, and better understanding is needed of factors aside from production regime that determine nutrient content.
Better science needed
The review comes with strong limiting factors. Notably, a large number of studies were excluded because they did not specify an organic certifying body, there was no information on the cultivar or livestock breed, no statement of which nutrient or nutritionally relevant substance was reviewed, no information on statistical methods, or no information on laboratory methods.
“We urge researchers investigating nutritional characteristics of organic food to improve the scientific quality of their work and propose the bare minimum when reporting,” the investigators wrote.
A second analysis including all 162 studies did return the same broad results on no nutritional differences. But by combining the results from different study designs and calculating standardised differences across foods by nutrient category, the “more nuanced findings from individual studies on specific foods were lost”.
The 162 studies also excluded studies in foreign languages that did not have English abstracts; the team could not locate 11 studies that may have contained relevant data; and two studies published after the cut off date were not taken into account.
In its communication on the findings, the FSA did not remark on the standard of studies included.
The Soil Association said it was disappointed by the conclusions, and pointed out that the mean positive difference would have shown up higher levels of protein, beta carotein, flavonoids, copper, magnesium, phosphorous, potassium, sodium, sulphur, zinc and phenolic compounds.
In addition the review did not take into consideration public health or environmental benefits of organic production methods such as regulating chemical fertilisers, herbicides and pesticides. Such chemicals may end up in the foodstuff.
“The potential for any benefits to public and environmental health of these actions would certainly warrant further systematic review,” wrote the researchers.
A spokesperson for the Soil Association told FoodNavigator.com that the reporting on the study in the mainstream press had been quite balanced, and the organisation is hopeful that the study will not knock consumer confidence in organics.
“Committed consumers who have been buying organic all through the recession will not stop. They see the bigger picture,” she said.
American Journal of Clinical Nutrition
Nutritional quality of organic foods: a systematic review
Authors: Dangour, A; Dodhia, S; Hayter, A; Allen, E; Lock, K; Uauy, R.