Most everyone who has ever selected their fruits and vegetables from the "organic" section while grocery shopping probably thought they were doing something good for their bodies and the environment.
Yet the question of whether organic foods are in fact more nutritious than their conventionally grown counterparts remains a topic of heated scientific debate.
On Monday, the British Journal of Nutrition published research that disputed the notion that organic foods are essentially no more healthful than conventional foods.
After reviewing 343 studies on the topic, researchers in Europe and the United States concluded that organic crops and organic-crop-based foods contained higher concentrations of antioxidants on average than conventionally grown foods.
At the same time, the researchers found that conventional foods contained greater concentrations of residual pesticides and the toxic metal cadmium.
"This shows clearly that organically grown fruits, vegetables and grains deliver tangible nutrition and food safety benefits," said study coauthor Charles Benbrook, a research professor at Washington State University's Center for Sustaining Agriculture and Natural Resources.
However, the study's findings came with some caveats.
"The first and foremost message is people need to eat more fruits and vegetables," Benbrook said. "Buying organic is the surest way of limiting exposure if you have health issues, but by all means, people need to increase their consumption of fruits and vegetables whether it's organic or conventional."
To carry an organic label in the U.S., foods must be grown without synthetic pesticides, growth hormones, antibiotics, genetic engineering or chemical fertilizers.
Scientists have hypothesized that organic plants produce more antioxidants and natural toxins to defend themselves against insects and other environmental threats.
It's not entirely clear to scientists whether the human body can absorb the extra antioxidants in organic foods and put them to use.
Although Benbrook and his colleagues said they suspected the antioxidants could be used by the body to combat damaging free radicals, they could not say so conclusively.
"It is important to point out that there is still a lack of knowledge about the potential human health impacts of increasing antioxidant/polyphenolic intake levels and switching to organic food consumption," the study authors wrote.
Despite prohibitions on using synthetic pesticides, up to 25% of organic crops contain pesticide residues because of contamination during packaging or from trace amounts in drifting soils or tainted irrigation water, some researchers have said.
When comparing organic and conventional crops, Benbrook and his colleagues found that conventionally grown fruits and vegetables were four times more likely to contain pesticide residues. That finding was based on 11 of the examined studies and did not evaluate the quantity of pesticides, Benbrook said.
Defenders of conventionally grown crops argue that any pesticide residues found are too small to pose a health risk.
"Our typical exposures are at least 10,000 times lower than doses we can give to laboratory animals every day throughout their lifetimes and not cause any effects," said Carl Winter, a pesticide and food toxin expert at UC Davis, who was not involved in the study. "If your concerns about pesticide residues are leading you to reduce your consumption of fruits and vegetables, then I think you're doing yourself more harm than good."
The findings about antioxidants and pesticide residues were not as surprising as the finding that organic foods were 48% less likely to contain cadmium.
Study authors said it remained unclear why, and what the specific health consequences could be. More research was necessary, they wrote.
Cadmium, which also is present in cigarette smoke, can cause damage to the liver and kidneys at certain levels.
For that reason, the study authors said, people should try to minimize their cadmium intake. However, they wrote, "the exact health benefits associated with reducing cadmium intake levels via a switch to organic food consumption are difficult to estimate."
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