Followup Discussion on Organic Food and Health

Crystal Smith-Spangler from the Stanford team. 
Photo credit: Norbert von der Groeben.

Are Organic Foods Healthier Than Their Non-Organic Counterparts?

This seemingly simple question has proven to be very hard to answer. 

One one hand, a research team from Stanford University's Center for Health Policy essentially says no.  Their study, which drew lots of press in September 2012, found very little evidence of increased health benefits.  The Stanford study reviewed 237 previously conducted scientific papers on the subject.

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). There was also no difference in protein or fat content between organic and conventional milk, though evidence from a limited number of studies suggested that organic milk may contain significantly higher levels of omega-3 fatty acids.

On the other hand, a less publicized earlier study from Newcastle University, UK, showed that organic foods were healthier. That study, published in April 2011, also reviewed previously published research.

A meta-analysis of the published comparisons of the content of secondary metabolites and vitamins in organically and conventionally produced fruits and vegetables showed that in organic produce the content of secondary metabolites is 12% higher than in corresponding conventional samples ( P< 0.0001). This overall difference spans a large variation among sub-groups of secondary metabolites, from a 16% higher content for defence-related compounds ( P< 0.0001) to a nonsignificant 2% lower content for carotenoids, while vitamin C showed a 6% higher content ( P= 0.006).

With such conflicting messages, what are consumers to think?

Luckily, in October 2012, the New York Times tried to explain, if not reconcile the different results.

So why the chasm? Part of the issue is methodology. Neither the Stanford nor the Newcastle researchers conducted new field or laboratory work; rather, both groups performed a meta-analysis, a statistical compilation of earlier work by others. It was a meta-analysis, for example, that revealed the effectiveness of aspirin in preventing the recurrence of heart attacks.

Such analyses seek out robust nuggets in studies of disparate designs and quality that offer confounding and often conflicting findings, especially in nutrition and medicine. The way the data from various studies is divvied up or combined in a meta-analysis can make a big difference in the conclusions. In the organic food research, some studies reported many measurements, some only a few. Some included several crops grown over multiple years, while others looked at only a few samples.

There it is:  two large "meta" studies; two different conclusions.  There was at least one result in common, however.  Organic food has less pesticide residue than its non-organic counterpart.  Again, there's a catch.  There aren't definitive human health studies linking the lower pesticide residue to improved human health. 

Thoughts?