The believers in the organic religion had a heyday earlier this week when a bunch of organic farming researchers published an article in the British Journal of Nutrition (BJN) that found, (gasp), that organic crops are more nutritious than conventional crops. Specifically, the researchers put together an meta-analysis of 343 studies that in some way related to the nutritional aspects of organically and conventionally produced crops. They found…
…organic crops, on average, have higher concentrations of antioxidants, lower concentrations of Cd [cadmium] and a lower incidence of pesticide residues than the non-organic comparators across regions and production seasons.
Based on these results should you rush out to Whole Foods right now? Probably not.
This meta-analysis was doubtlessly undertaken to counter two earlier meta-analyses that found no signficant nutritional differences between organic and conventional crops. The first was published in 2009 in the American Journal of Clinical Nutrition which reported:
On the basis of a systematic review of studies of satisfactory quality, there is no evidence of a difference in nutrient quality between organically and conventionally produced food-stuffs. The small differences in nutrient content detected are biologically plausible and mostly relate to differences in production methods.
A larger study published in the Annals of Internal Medicine in 2012 found:
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.
So did the new study find anything of consequence with regard to how consuming organic foods affects human health? Not really.
It is possible (probable even) to quibble with how any meta-analysis is put together. For example, the organic researchers in the new BJN study assert:
The main reason for the inability of previous studies to detect composition differences was probably the highly limited number of studies/data sets available or included in analyses by these authors, which would have decreased the statistical power of the meta-analyses.
Well, maybe. Alan Dangour, a researcher associated with the earlier meta-analyses that found no signficant nutritional differences returns the favor of criticism:
The authors of this new systematic review that primarily aims to identify differences in nutrient content between organically and conventionally produced foods have brought together a large number of studies published over a 20 year period. The quality of the available data varies greatly and it is therefore very surprising that, in their analysis, the authors decided to include all the data that they found, irrespective of their quality. In fact the study authors themselves note that there are significant concerns with the consistency and reliability of some of their findings. Mixing good quality data with bad quality data in this way is highly problematic and significantly weakens confidence in the findings of the current analysis. It is a shame that greater care was not taken in trying to ensure that the analyses were based only on reliable and scientifically robust data from satisfactory quality studies.
So it goes.
Interestingly, many head-to-head comparisons in which organic crops are grown next to conventional ones find no important differences in nutrition. For example, a 2009 study comparing many of the same anti-oxidant compounds in the BJN study between organic and conventional wheat found "no statistically significant differences between the two farming systems." A 2011 study on tomatoes reported that "organically grown tomato is no more nutritious than conventionally grown tomato when soil fertility is well managed." On the other hand, a same farm study in 2010 did find that "organic management and fertilization have a positive effect on the accumulation of certain beneficial minerals and phenolic compounds in eggplant."
Given these sorts of contradictory findings, it is possible to cherry-pick your way to the results you want. Not that anybody would ever do that.
But let's assume the results are real. Do they have any appreciable health consequences for people? Consider, for example, a 2014 prospective study comparing women who regularly eat organic foods with those who don't that concluded:
In this large prospective study there was little or no decrease in the incidence of cancer associated with consumption of organic food, except possibly for non-Hodgkin lymphoma.
A 2011 study of the risks posed by pesticide residues on conventional crops concluded that…
…(1) exposures to the most commonly detected pesticides … pose negligible risks to consumers, (2) substitution of organic forms of the twelve commodities for conventional forms does not result in any appreciable reduction of consumer risks….
What about the higher levels of toxic cadmium in conventional crops? Those levels tend to depend on the soils in which crops are grown, not the method of cultivation. The study does not appear to have controlled for such variations. In any case, a 2007 Belgian study found that organic crops can contain higher levels of cadmium than conventional ones.
Finally, the findings on anti-oxidant levels were the chief reason the study got the attention of the media. Do they matter with regard to human health? Charles Benbrook, one of the researchers in the BJN study acknowledges:
Our team, and indeed all four reviews, acknowledges that many questions remain about the bioavailability of plant-based antioxidants, how necessary they are at different life stages, and how inadequate intakes shift the burden of disease. But our view is that the weight of evidence supports linkages between higher antioxidant intakes and improved health outcomes, despite inability to quantity such linkages or predict fully which factors drive them.
Actually, the weight of the evidence strongly indicates that eating 5 to 9 servings of fruits and vegetables every day—either grown conventionally or organically—provides significant health benefits, including those associated with the consumption of plant-derived anti-oxidant compounds. Interestingly, the BJN study found…
…significantly higher concentrations of total carbohydrates and significantly lower concentrations of proteins, amino acids and fibre in organic crops/crop-based compound foods.
Somewhat amusingly, the authors observe:
The nutritional significance/relevance of slightly lower protein and amino acid concentrations in organic crops to human health is likely to be low, as European and North American diets typically provide sufficient or even excessive amounts of proteins and essential amino acids.
Of course, exactly the same thing can be said with regard to plant anti-oxidants among those Europeans and North Americans who eat their recommended daily servings of fruits and vegetables however grown.
"The additional cost of organic vegetables to the consumer and the likely reduced consumption would easily offset any marginal increase in nutritional properties, even if they did occur, which I doubt. To improve public health we need to encourage people to eat more fruit and vegetables, regardless of how they are produced."
Big tip of the hat to Brad Plumer over at Vox whose links I shamelessly mined.