STANFORD, Calif. — A new study out of Stanford University calls into question the superior nutritional and health benefits of eating organically grown food.

The study, Are Organic Foods Safer or Healthier Than Conventional Alternatives?, was published in the most recent issue of Annals of Internal Medicine. Among the findings are that organically grown food is not significantly more nutritious than conventionally grown food. These include grains, meat and milk.

The study did find, however, that conventionally grown or raised food contained more antibiotic-resistant bacteria and more pesticide residues than organic foods.

The study is a literature review examining 237 published studies in the English language. The review noted between 1997-2010, U.S. sales of organic foods increased from $3.6 billion to $26.7 billion and that consumers can pay up to twice as much for organic than conventional foods.

It also stated organic certification requirements and farming practices vary worldwide, but organic foods are usually grown without pesticides or fertilizers, or the routine use of antibiotics or growth hormones.

People buy organic for different reasons, the authors stated; these include concerns about the effects of conventional farming on the environment, concerns about animal welfare, human health concerns and the perception that organic foods taste better.

“Despite the widespread perception that organically produced foods are more nutritious than conventional alternatives, we did not find robust evidence to support this perception,” the authors stated. “Of the nutrients evaluated, only one comparison, the phosphorus content of produce, demonstrated the superiority of organic foods ... although removal of one study rendered this result statistically insignificant.”

They went on to write that the phosphorus finding doesn’t matter anyway, because a person has to be at “near total starvation” before experiencing a deficiency of dietary phosphorus. The authors “did not find significant differences in the vitamin content of organic and conventional plant or animal products,” the report stated.

They also reported higher “total phenols” in organic food, but wrote that the difference is so small it’s basically insignificant. They also found more beneficial fatty acids in raw milk than conventionally grown milk, as well as more vaccenic acid.

Organically raised chicken was also found to have more W-3 fatty acids than conventional chicken. The other differences in fatty acids content between conventional and organic milk and chicken were “statistically insignificant,” it stated. The authors added that other studies have found that sampling any brand of milk affected fatty acid levels at least as much as the farming method.

Regarding pesticide contamination, the study found detectable residues were found in 7 percent of organic produce samples and 38 percent of conventional produce samples. Studies of meat, poultry, eggs and milk did not examine pesticide levels.

It also found that organic produce had 30 percent lower risk for contamination with any detectable pesticide residue than conventional produce. “However, the clinical significance of this finding is unclear because the difference in risk for contamination with pesticide residue exceeding maximum allowed limits may be small,” the report said.

There was also significantly more antibiotic-resistant bacteria in conventionally raised chicken than in organic chicken. The authors wrote this is probably because of the use of antibiotics in animal feed.

But “the extent to which antibiotic use for livestock contributes to antibiotic-resistant pathogens in humans continues to be debated because inappropriate use of antibiotics in humans is the major cause of antibiotic-resistant infections in humans.”

The authors concluded “the evidence does not suggest marked health benefits from consuming organic versus conventional foods, although organic produce may reduce exposure to pesticide residues and organic chicken and pork may reduce exposure to antibiotic-resistant bacteria.”

The research team was led by Dena Bravata, MD, MS, a senior affiliate with Stanford’s Center for Health Policy, and Crystal Smith-Spangler, MD, MS, an instructor in the school’s Division of General Medical Disciplines and a physician-investigator at VA Palo Alto Health Care System. According to Stanford, the authors received no external funding for this study.