Food that beckons from the organic aisles of grocery stores may not be any better for you than what lines the rest of supermarket shelves.
According to a British review of studies done over the past 50 years, organic and conventionally produced foods have about the same nutrient content, suggesting that neither is better in terms of health benefits.
"We did not find any important differences in nutrient content between organically and conventionally produced foods," said study author Alan Dangour, a registered public health nutritionist with the London School of Hygiene and Tropical Medicine.
Nonetheless, the researchers noted, organic foods continue to grow in popularity. In the United Kingdom, the market share for organic foods increased 22 percent from 2005 to 2007, they said.
Likewise, the market for organic foods in the United States has grown at about a 20 percent rate each year since 1990, reaching $13.8 billion in consumer sales in 2005, according to the Organic Trade Association. That represents 2.5 percent of total food sales in the country, the trade group noted.
"As a registered dietitian, it is good to see that a systematic review of the literature supports what has long been believed -- that the nutritional content of traditionally grown foods and organic foods are comparable," said Connie Diekman, director of university nutrition at Washington University in St. Louis and past president of the American Dietetic Association. "This report provides confirmation for consumers that if they choose conventionally grown foods or organic foods they will be meeting their nutritional needs."
The review zeroed in on 162 studies that dealt with the nutrient content of foods. Only 55 were of what the researchers considered to be "satisfactory quality" -- a strong indicator that, overall, the science on the subject is not up to snuff.
They found no noted differences between conventional and organic crops with regard to vitamin C, magnesium, calcium, potassium, zinc and copper content. Organic crops did have higher levels of phosphorus, and conventionally produced crops had higher levels of nitrogen.
No differences in nutrient content were indicated in the livestock studies, according to the review.
The Oregon-based Organic Center, which promotes organic food, conducted a similar review of the literature, said Charles Benbrook, chief scientist for the Center. That study yielded results similar to those in the British study, but it also found higher levels of healthy antioxidants and polyphenols in organic foods.
"Given that some of the most significant differences favoring organic foods were for key antioxidant nutrients that most Americans do not get enough of on most days, we concluded that the consumption of organic fruits and vegetables, in particular, offered significant health benefits, roughly equivalent to an additional serving of a moderately nutrient dense fruit or vegetable on an average day," Benbrook said.
And there's another aspect to the organic vs. conventional food debate, said Sheah Rarback, director of nutrition at the Mailman Center for Child Development at the University of Miami Miller School of Medicine.
"You have to also look at what you're not getting" with organic foods, she said. "Maybe it's not a big difference nutritionally, but conventional products may have more pesticides."
And that's a particularly important issue for children, she said.
"We know that young children are getting the nutrition, whatever choice they make, but we also have to look at the pesticide issue," Rarback said. "A study published in Environmental Health Perspectives found that children eating conventionally grown fruit had pesticide residue in their urine, which decreased after just five days on an organic diet."
The production of organic food is subject to a variety of regulations, including those that govern the use of pesticides and other chemicals in fruits and vegetables and the use of medicines in animals, the authors of the review noted in their study, which will be published in the September issue of the American Journal of Clinical Nutrition.
Rarback indicated that the ability to get solid research on organic versus conventionally produced products is hampered by variations in the production process.
"There are so many variables," she said. "Where is something grown? Where is it shipped from? How long was it on the truck? There are going to be variables in terms of nutrition just from production methods."
There's more on food and the nutrients in food at the United States Department of Agriculture.
SOURCES: Alan Dangour, registered public health nutritionist, London School of Hygiene and Tropical Medicine; Connie Diekman, M.Ed, R.D., L.D., director, university nutrition, Washington University, St. Louis, and past president, American Dietetic Association; Sheah Rarback, R.D., director, nutrition, Mailman Center for Child Development, University of Miami Miller School of Medicine, Miami; Charles Benbrook, Ph.D., chief scientist, The Organic Center, Enterprise, Oregon; September 2009 American Journal of Clinical Nutrition