From a nutritional standpoint, are organic foods worth the added cost?
No, according to the authors of a meta-analysis study released today in the Annals of Internal Medicine. After examining the findings of more than 200 previously published studies, researchers from Stanford University concluded that there is no “strong evidence that organic foods are significantly more nutritious than conventional foods.”
The meta-analysis did find, however, that organic fruits and vegetables are significantly less likely to contain pesticide residues than conventionally grown produce and that organic chicken and pork are less likely to be contaminated with antibiotic-resistant bacteria.
U.S. sales of organic food — produce and grains grown without synthetic pesticides or fertilizers and animals raised without the routine use of antibiotics or growth hormones — have skyrocketed in recent years, jumping from $3.6 billion in 1997 to $26.7 billion in 2010. Depending on where you purchase your groceries, organic foods can cost up to twice as much as their conventional counterparts.
The findings of this meta-analysis, therefore, have economic as well as health ramifications. But although its authors conclude that organic foods are probably not worth the added cost, the study itself seems to be more equivocal.
Here are the major findings:
- There were no consistent differences in the nutrient content of organic and conventional foods. Organic foods did contain more phosphorus, but as the study’s authors point out, that finding was “unlikely to be clinically significant because near-total starvation is needed to produce dietary phosphorus deficiency.”
- The Stanford researchers did find higher levels of omega-3 fatty acids, which may help prevent heart disease, in organic milk and chicken. They also found that organic produce contained higher levels of phenols, which have been associated with a reduced risk of cancer. But, added the researchers, these differences between organic and conventional foods varied widely from study to study, so the results must be viewed with caution.
- Organic produce was much less likely to be contaminated with pesticides than conventional produce. Some 38 percent of the conventional foods tested in the studies contained pesticides compared with 7 percent of the organic foods. (Organic foods can become contaminated with pesticides when the chemicals drift over on the wind from nearby non-organic fields.) The levels of pesticides found on all the food were within current federal safety levels, however. (Not mentioned in the study is the argument made by environmentalists and food-safety activists that the current safety levels are too high, particularly to protect children.) Two of the studies reviewed by the Stanford researchers found that when children were switched to an organic diet for just five days, the amount of pesticides in their urine dropped significantly.
- Organic chicken and pork were 33 percent less likely than conventionally raised meat to contain antibiotic-resistant bacteria. The researchers said the clinical significance of this finding is unclear.
- The organic produce had a slightly higher risk of being contaminated with Escherichia coli (E. coli), which can cause a type of food poisoning that is sometimes life-threatening. (The higher risk appeared only after the researchers eliminated a study involving lettuce from their calculations.)
This meta-analysis, as its authors point out, had many limitations. The studies it examined included food raised and tested in many different ways, a factor that makes comparing them difficult. Various methods of testing for pesticides were used, for example. In addition, the fruits and vegetables tested included varieties with different genetic make-ups; they were also harvested at different times in the growing season and under different weather conditions — all factors that can influence nutritional content.
Still, these are interesting findings. Will they change anybody’s shopping habits? I doubt it. For although 51 percent of respondents to a 2010 Nielson survey of organic-food consumers said they purchased organic foods because “they are more nutritious,” 53 percent said they did so to “avoid pesticides and other toxins.”