September 11th, 2012

Organic Foods May Not Be More Nutritious

Reviewed by Robert Jasmer, MD; Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

Action Points
--There's no solid evidence that organic foods are healthier than those produced
conventionally.
--Point out that organic foods may expose patients to fewer pesticide residues and
fewer antibiotic-resistant bacteria.

There's no solid evidence that organic foods are healthier than those produced conventionally, according to a review of several studies.

Although no long-term trials have looked at the differences in health outcomes for people who eat a largely organic diet versus a conventional one, the few small trials that have examined clinical outcomes found no differences in allergic outcomes or food poisoning, according to Crystal Smith-Spangler, MD, of Stanford University in Palo Alto, Calif., and colleagues.

"Despite the widespread perception that organically produced foods are more nutritious than conventional alternatives, we did not find robust evidence to support this perception," they wrote in the Annals of Internal Medicine online.

Organic foods may, however, expose patients to fewer pesticide residues and fewer antibiotic-resistant bacteria, they noted.

Between 1997 and 2010, sales of organic foods in the U.S. rose from $3.6 billion to $26.7 billion, and consumers can pay up to twice as much for organically produced foods.

Organic certification requirements and farming practices vary widely, but some requirements for organic foods and livestock are:

1. Grown without synthetic pesticides or fertilizers
2. Processed without irradiation or chemical food additives
3. Not grown from genetically modifed organisms
4. No antibiotics or growth hormones
5. Organically produced, pesticide-free animal feed

To assess whether folks are gaining any health advantages for their additional expenses, Smith-Spangler and colleagues reviewed 17 studies in humans and 223 studies of nutrient and contaminant levels in foods that were conducted between January 1966 and May 2011.

Among the three human studies that assessed clinical outcomes, the researchers saw no significant differences in allergies including eczema, wheeze, and atopic sensitization, or in food poisoning as defined by symptomatic Campylobacter infection.

Nor did any of the nutrient studies find any clinically meaningful differences between organic and conventional foods in terms of levels in serum, urine, breast milk, or semen, they reported.

Only phosphorus levels were significantly higher in organic produce, but the difference isn't likely to have clinical significance because "near-total starvation is needed to produce dietary phosphorus deficiency," they wrote.

The researchers also found an overall 30% higher risk for contamination with pesticide residues in conventional products compared with organic ones, and two studies reported lower urinary pesticide levels among children on organic diets.

Yet the clinical significance of the finding again was unclear because the difference in risk for contamination with residues that exceeded maximum allowed limits was small, they reported.

People on organic and conventional diets are at about the same risk for food poisoning, the researchers said, with equal contamination by Salmonella and Campylobacter species seen in both types of food.

But conventionally produced pork and chicken does appear to carry a 33% higher risk for bacteria that's resistant to 3 or more types of antibiotics, they noted.

That may be related to the routine use of antibiotics in conventional animal farming, they said. Still, they cautioned that "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."

Smith-Spangler and colleagues warned that there have been no long-term studies of health outcomes among patients who eat a predominantly organic diet versus one full of conventionally produced foods.

Their review was also limited because the included studies were heterogeneous and susceptible to publication bias, they added.

Still, they concluded that 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 researchers reported no conflicts of interest.

Primary source: Annals of Internal Medicine
Source reference:
Smith-Spangler C, et al "Are organic foods safer or healthier than conventional alternatives?" Ann Intern Med 2012; 157: 348-366.