The new review – published in Annals of Internal Medicine – analysed data from more than 200 published nutrient analysis studies and human trials, finding that there is generally no difference in nutritional value or risk for bacterial contamination between organic and conventional foods.
The research team, led by Crystal Smith-Spangler of Stanford University, said their findings suggest consumption of organic fruits and vegetables has no benefit over conventional foods in terms of improving health.
"Some believe that organic food is always healthier and more nutritious," said Smith-Spangler. "We were a little surprised that we didn't find that."
Dr Dena Bravata, senior author of the review added: "There isn't much difference between organic and conventional foods, if you're an adult and making a decision based solely on your health."
The team did find that organic food consumption reduced exposure to any detectable pesticide residues by around 30%, but noted that pesticide levels were generally within the allowable limits for safety anyway.
The researchers said their aim is to educate people, not to discourage them from making organic purchases: "If you look beyond health effects, there are plenty of other reasons to buy organic instead of conventional," said Bravata.
“Consumers may choose to purchase organic foods for other reasons besides nutrition and food safety, such as concern for animal welfare, the environment, or preferences in taste," added Smith-Spangler.
Organic foods are often twice as expensive as their conventionally grown counterparts, said the authors.
Though there is a common perception — perhaps based on price alone — that organic foods are better for you than non-organic ones, the authors noted that there is an open question as to whether they have added health benefits.
Bravata said that the evidence to back the supposed and often presumed benefits of organic consists of a "confusing body of studies, including some that were not very rigorous, appearing in trade publications."
"This was a ripe area in which to do a systematic review," said Smith-Spangler.
Smith-Spangler and her colleagues conducted the systematic review (found in full here ) of 17 human studies and 223 studies of nutrient and contaminant levels in unprocessed foods including fruits, vegetables, grains, milk, eggs, chicken, pork, and meat.
The team compared the health, nutritional, and safety characteristics of organic and conventional foods, finding that the published literature “lacks strong evidence that organic foods are significantly more nutritious than conventional foods.”
After analyzing the data, they found found little significant difference in health benefits between organic and conventional foods.
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. Smith-Spangler and her colleagues said 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 the team did find weak evidence of the nutritional superiority of organic foods in that organic produce contained significantly higher levels of total phenolic compounds, which have antioxidant properties, and that organic milk and chicken contained higher levels of omega-3 fatty acids.
While researchers found that organic produce is 30% less likely to be contaminated with pesticides than conventional fruits and vegetables, the reviewers noted that organic foods are not necessarily 100% free of pesticides. In addition, the pesticide levels of all foods fell within the allowable safety limits, they said.
Source: Annals of Internal Medicine
Volume 157, Number 5, Pages 348-366, doi: 10.7326/0003-4819-157-5-201209040-00007
“Are Organic Foods Safer or Healthier Than Conventional Alternatives?: A Systematic Review”
Authors: Crystal Smith-Spangler, Margaret L. Brandeau, Grace E. Hunter, J. Clay Bavinger, Maren Pearson, et al