As more and more consumers go organic, a new study has renewed debate over the potential harms and benefits of organic foods.
Many studies have found that, vitamin for vitamin, organic foods are nutritionally equal to their conventional counterparts. In clinical studies, people who eat organic food tend to be no healthier than those who don’t. But a new analysis of data from 343 published studies finds that, compared with conventionally grown foods, organic plant-based foods may pack 20 to 40 percent more antioxidants and around 48 percent less cadmium, a cancer-causing metal. The study appeared June 26 in the British Journal of Nutrition.
“The totality of the evidence is that there are higher levels of nutrients in organic foods,” says study coauthor Charles Benbrook, an agricultural researcher with Washington State University.
Like some earlier studies that drew opposing conclusions, the new work is a meta-analysis. Such studies harvest and analyze data from a collection of other studies rather than producing new data. A 2012 meta-analysis included data from 240 studies and found no nutritional benefits in organic over conventional foods. The authors say their new study contradicts older analyses because it includes more data and uses a statistical method that they argue is better.
Experts warn that meta-analyses can yield bogus results if they include poor-quality experiments or try to compare disparate datasets. The latter problem may plague the new study, says food and nutrition researcher Shahla Wunderlich of Montclair State University in New Jersey. The study includes analyses of organic food from areas around the world with varying climates, soil types, pests and farming practices. Those factors influence food’s nutrients, Wunderlich says. “Regardless of organic versus conventional, the nutritional value would be different,” she says.
Wunderlich was also concerned about possible bias in the study: It received some of its funding from the Sheepdrove Trust, a charity that supports organic farming.
Even if the findings from this latest meta-analysis are accurate, still unclear is whether the reported differences are relevant to health. Although organic foods had lower levels of cadmium, the levels found on conventional crops were still below safety limits set by federal agencies.
And the benefits of extra antioxidants are also murky, Benbrook says. Researchers had long hypothesized that antioxidants such as vitamin E and beta-carotene improve heart health and fight cancer. But, clinical studies have been largely inconclusive. The new analysis also found that organic foods contain less protein, amino acids and fiber than conventional food.
Why organic crops would contain less cadmium and more antioxidants is also a puzzle. The authors speculate that organic crops may make more antioxidants because they make less sugar than conventional crops do. Conventionally grown crops may sometimes receive a surplus of nitrogen fertilizer, which could alter plants’ metabolism to make more sugars and less antioxidants. The authors also wonder if the increase in antioxidants is directly caused by organic farming’s lower use of pesticides, because plants make some antioxidants as defense against pests, and organic crops may suffer more from pests.
“It’s certainly possible,” says plant microbiologist Gwyn Beattie of Iowa State University in Ames, and further tests could bear out the hypothesis. But she points out that plants make the defensive antioxidants even when they’re not attacked.
For now, nutrition experts like Wunderlich say that at least one thing is clear for healthful eating: the importance of eating produce. “I’d rather see people eat all kinds of food and have lots of fruits and vegetables in their diet, whether they’re organic or not,” she says.