A study began to be trumpeted last Friday that purported to show that organic crops had lower pesticide levels and higher antioxidant levels than conventionally farmed crops. The study is to be published this week in the British Journal of Nutrition, and is titled "Higher antioxidant and lower cadmium concentrations and lower incidence of pesticide residues in organically grown crops: a systematic literature review and meta-analysis." So there are a bunch of press releases on a yet to be published paper? This is not the usual approach.
The lead author is Marcin Baranski of Newcastle University, along with 17 co-authors. The paper is a meta analysis, meaning that the authors re-analyzed published papers, in this case 345 of them and tabulated their measurements statistically.
But, if we look at the spokesman most frequently interviewed on this not-yet paper, we mostly see quotes from Dr Charles Benbrook, at Washington State University. Benbrook is an agricultural economist by training, not a scientist and is well-known as a proponent of organic farming. He is one of the co-authors of this study, which was sponsored by the European Community and the Sheepdrove Trust, who “supports R&D on organic and sustainable farming.”
There have been two previous studies, both finding nutritional equivalence between the farming methods: one by Dangour in 2009 (162 articles), and one by Smith-Spangler et. al. from Stanford (223 studies). Both did similar meta-analyses but found no significant difference in nutrients between organic and conventional crops.
So why was another study necessary? One could guess that they wanted to do a study that would make organic foods come out looking better. In fact, the Science Media Centre was quite critical of this study:
For many of the outcomes considered there was evidence for moderate or strong publication bias. Publication bias can lead researchers to find effects that are not real; this is exacerbated when using a random effects meta-analysis (as here) – even more so if the meta-analysis is unweighted (also used here).
The principal finding in this paper was that organic crops had greater concentrations of anti-oxidants. This is shown in several tables. However buried in the discussion on page 14, you will find that “the concentrations of proteins, amino acids and N…were found to be lower in organic crops.”
In fact, despite the pages they spend on them, anti-oxidants are not nutrients and may not even be beneficial at all. And, in a BBC report, Professor Richard Mithen, leader of the food and health program at the Institute for Food Research said that
"The references to 'antioxidants' and 'antioxidant activity', and various 'antioxidant' assays would suggest a poor knowledge of the current understanding within the nutrition community of how fruit and vegetables may maintain and improve health."
Finally, in a New York Times article, Professor Dangour, author of 2009 study, is quoted:
He said the researchers erred in not excluding the weaker studies from the analysis. “To my mind, there’s no convincing evidence that these foods are different in nutritional composition,” he said.
It’s important to note that organic certification is, as then agriculture Secretary Dan Glickman said,
“Let me be clear about one thing. The organic label is a marketing tool. It is not a statement about food safety. Nor is ‘organic’ a value judgment about nutrition or quality.”