In July of 2014, the British Journal of Nutrition published a 343 study meta-analysis which has been used as justification for concluding that organic foods are more nutritious than their conventionally grown counterparts. In a nutshell, its most relevant claims are that organic produce contained lower pesticide residues, higher anti-oxidant concentrations and lower cadmium levels than their conventional counterparts.
The meta-analysis was performed by a team of scientists led by Carlo Leifert, professor of ecological agriculture at Newcastle University in England, and was funded in part by the European Union, and in part by the Sheepdrove Trust, an organization which, it its own words, “supports initiatives which increase sustainability, biodiversity and organic farming.”
The Sheepdrove trust’s mission statement may raise suspicions of conflict of interest, but it does not in-and-of-itself constitute a valid justification for dismissing its claims as invalid; at worst, it’s merely a red flag. Research must ultimately be evaluated on its own merits, and not on the perceived biases of the people involved.
Since this was a meta-analysis, no new original research was done by Leifert or his colleagues for this paper. As many of our readers are already aware, in a meta-analysis, a researcher compiles a large body of the existing studies on a particular topic, usually discarding those that are methodologically unsound, and then chooses a statistical method with which to combine them. A good meta-analysis turns a series of smaller studies into one large one, which, if done well, supplies greater clout and can bring clarity to controversial and/or over-politicized scientific sub-topics. Many systematic reviews of scientific literature will include a meta-analysis as part of their investigation.
That said, there are reasonable grounds for rejecting the meta-analysis purporting that organic foods are more nutritious which do not rely on merely rejecting it on the grounds of the suspected personal biases of the authors or their funding organizations. For instance:
1. The study used very open criteria, and therefore included more lower-quality studies than other meta-analyses would likely include. It is likely that the inclusion of weaker studies biased the results of this latest analysis in favor of a false positive. Good meta-analyses have to have stringent quality control standards in their vetting process so as not to skew the results.
2. The studies were rigged by only testing for conventional pesticides, so it’s unsurprising that there were more of those on conventional produce. They fail to mention that those amounts were way below the safe tolerance limits, and are highly unlikely to have any effect whatsoever on the healthiness of the produce. Organic proponents claim that, even if their individual levels are safe, what matters is their accumulative effect over time, but this is pure speculation with no actual evidentiary basis.
3. They didn’t test for organic pesticides at all, and there is no valid reason whatsoever to conclude that organic pesticides are safer than synthetic pesticides; proponents merely assume that they are safer on the grounds that they are naturally occurring, which is a complete non sequitur. Arsenic, black widow venom and ricin are naturally occurring, but that doesn’t mean they’re good for you. That’s a perfect textbook example of the naturalistic fallacy.
4. Both the abstract and the subsequent reporting conspicuously omitted other consequences of their meta-analysis which didn’t support their narrative, such as the fact that the study also found that organic produce has lower levels of protein, fiber, and nitrates.
5. As for the cadmium, while levels were higher in conventional produce, they neglected to mention that the levels were still well below safety limits. Again organic proponents argue that the levels accumulate, but they still have no evidence for this.
6. The reporting on this review was misleading in regards to the anti-oxidants. They make it sound as though more anti-oxidants = more healthy, when the truth is that the relationship between health and anti-oxidant intake is far more nuanced and complex than that.
7. Their results are contradicted by several other independently funded studies and systematic reviews exploring the same question, which makes this particular one an outlier.
For example, a 2009 review by Dangour et. al. concluded:
“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 foodstuffs. The small differences in nutrient content detected are biologically plausible and mostly relate to differences in production methods.”
Another one the following year (also by Dangour et al) came to similar conclusions:
“From a systematic review of the currently available published literature, evidence is lacking for nutrition-related health effects that result from the consumption of organically produced foodstuffs.”
A 2012 review by Smith-Spangler et. al concluded:
“After analyzing the data, the researchers found little significant difference in health benefits between organic and conventional foods. No consistent differences were seen in the vitamin content of organic products, and only one nutrient — phosphorus — was significantly higher in organic versus conventionally grown produce (and the researchers note that because few people have phosphorous deficiency, this has little clinical significance).”
Moreover, older reviews came to similar conclusions, as you can see for yourself here:
All of these reviews of the data were independently funded, yet this one claiming the opposite conclusion was partially funded by the Sheepdrove Trust, which is known for funding research in support of organic farming.
If you knew that, out of a whole bunch of studies and reviews of a particular new drug, the only one that came out in favor of the drug was one by the drug company seeking to patent it, and that some of the conclusions based on it were not entirely supported by the data, then you’d be reasonable to harbor trepidation towards its conclusions. So, why wouldn’t you have similar trepidation about a review like this which is not merely funded in part by a pro-organic group, but also contradicts the independent research that’s been done? That doesn’t seem very reasonable, does it?
For further reading on this subject, I recommend the following:
– Credible Hulk (StASM admin)