A systematic review of 162 scientific papers published in the scientific literature over the last 50 years, however, found there was no significant difference.
The study's abstract, on the other hand, says something slightly different:
From a total of 52,471 articles, we identified 162 studies (137 crops and 25 livestock products); 55 were of satisfactory quality. In an analysis that included only satisfactory quality studies, conventionally produced crops had a significantly higher content of nitrogen, and organically produced crops had a significantly higher content of phosphorus and higher titratable acidity.
In other words, the study didn't include 162 papers, but fifty-five. Again, maybe that doesn't change anything in the study, but it inflates the scope of the study as presented to Reuters readers.
The study's conclusion is that "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." I'm not sure what the distinction is between "nutrient quality" and "nutrient content" is, but my guess is that these differing levels of nitrogen, phosphorus, and "titratable acidity" (whatever that is) don't provide the consumer with significant health benefits. I couldn't say--I'm not a nutritionist.
It's worth noting that this study is criticized by those we'd expect to see criticism from, such as the Soil Association, a British organization that promotes organic farming. The Soil Association's response to the study is interesting, because they include some of the study's findings (and I can't access the study itself because I'm not a member of the American Society of Clinical Nutrition or any other Nutritiony organization). The Soil Association claims that the researchers found higher levels of several nutrients in organic produce, including protien, flavonoids, copper, magnesium, phosphorus, potassium, sodium, sulphur, zinc, and phenolic compounds. They also cite a beta-carotene level 53.6% higher in organic produce. They also found "higher levels of beneficial polyunsaturated fatty acids in organic meat and dairy products (between 2.1% - 27.8% higher) compared to non-organic meat and dairy." Again, I'm no nutritionist, but I'd be curious just how significant those differences are.
The Soil Association has other complaints about the study, but most of those are outside of the intended scope of the study, like the lack of information on "the long-term effects of pesticides on human health." That may be true, but that's a criticism of the general dialogue about organic food rather than of this study specifically.
The debate about the benefits of organic food involves more than just its nutritional component. Actually, the nutritional aspect of organic farming doesn't carry much weight at all. In their book The Ethics of What We Eat , Peter Singer and Jim Mason acknowledge that studies in Europe had already been finding little difference in nutritional values when they published in 2006. They focus their attention on other benefits to organic farming, such as better maintenance of soil quality, biodiversity among incidental plants and animals, pollution reduction, and the significant reduction of pesticides and herbicides. They cite a study in their "Going Organic" chapter that struck me as important:
Scientists at the University of Washington tested the urine of children eating a conventional diet and children eating predominantly organic produce and found that . . . differences in pesticide levels are detectable in our bodies. Some of the children on a conventional diet had pesticide byproducts in their urine that indicated an intake of pesticides above the "negligible risk" level recommended by the Environmental Protection Agency's guidelines. The children who ate organic foods had a median level of pesticide byproducts only one-sixth that of children eating conventionally farmed foods, suggesting that their intake of pesticides was well within EPA recommended limits.