Despite the national controversy surrounding the results of an organic food study by Stanford researchers, the study’s authors stand by their results.

The study, which disputed the health benefits of organic food, was published on Sept. 4 in the Annals of Internal Medicine. It made headlines in national media outlets soon thereafter. Yet, within days, critics began to cast doubts on the study’s methodology and funding, crowned by an Oct. 2 column by Mark Bittman of The New York Times. Bittman called the study “junk science.”

Lead authors Dena Bravata, an adjunct affiliate at the Center for Health Policy, and Crystal Smith-Spangler, instructor at the School of Medicine, decided to conduct the study because their patients often asked whether or not organic food was a healthier option than conventional alternatives.

“I am a physician. My patients ask me about organic food or conventional food and what the differences are and so it was really just to learn [for] ourselves and then we thought it would be of interest to others, hence the publication,” Smith-Spangler said.

The study focused exclusively on the nutritional, health and safety aspects of organic versus conventional food, including fruits, vegetables, grains, meats, milk, poultry and eggs. Processed food was not studied.

Results showed that organic foods offered little notable nutritional benefits and rarely contained additional vitamins when compared to its conventional counterparts. Findings indicated that the only nutritional benefit of organic food is the higher levels of phosphorous they contained. However, the authors pointed out that extra phosphorous provides little health benefit because few people have depleted levels of the mineral.

Despite the purported lack of nutritional benefit from organic food, the study found that conventional food contained 30 percent more pesticides than organic foods and that antibiotic resistant bacteria were less likely to live in organic chicken and pork. Even so, the authors stated that both organic and conventional options fall within food safety regulations and that not all organic food is pesticide-free.

To arrive at these results, researchers did not conduct any original research. Instead, they relied on past studies using a statistical tool known as meta-analysis.

Ingram Olkin, professor emeritus of statistics developed this model of statistical analysis, which is used to combine and assess the results of multiple, independent studies. The researchers applied meta-analysis to compile past research done on the health of organic foods and discern a single conclusion. The method is criticized by some in the field.

Over the past four years, the team read thousands of studies going back decades to narrow their research down to 237 peer-reviewed papers, which they then scrutinized with meta-analysis. 223 of the studies evaluated the nutrient, bacterial, fungal or pesticide content of conventional and organic foods. Although the research was comprehensive, Olkin said that the results are not definitive because the evidence analyzed was weak.

“When data is not strong, two people looking at the data can easily see differences,” Olkin said.

Indeed, in April 2011, a team from Newcastle University in England also performed meta-analysis and found slightly different results. According to their study, vitamin C content is higher in organic foods.

Critics of the study argued that meta-analysis done exclusively by statistical experts neglects the input of scientists who study organic food.

“They are really good at that analysis but I do not think that is quite enough,” said Associate Professor of Medicine Christopher Gardner. “I think you have to get experts in the field of the study that you are pooling.”

Professor of Engineering and co-author of the study Margaret Brandeau rejected this suggestion.

“We did not really think we needed someone who knows about organic food. We need someone who knows about how to interpret statistical results of studies,” she said.

Another area that came under criticism was the source of funding for the research. Critics accused the authors of bias because of Stanford’s financial ties to agricultural companies like Cargill, Inc. and Monsanto Company.

Cargill and Monsanto are both agricultural giants in the food production industry. Both companies have reportedly donated to Stanford’s Freeman Spogli Institute (FSI). In particular, Cargill has worked with Stanford for 25 years in the Food, Security and the Environment (FSE) program. It has donated $3 million to the University, with another $2 million pledged. The Center for Health Policy, with which Bravata and Smith-Spangler are affiliated, is part of FSI.

However, the Stanford team asserts that neither the FSI nor the money that Cargill donated to FSE was directly associated with any of the research conducted for the study.

“We did not have anything to do with this study,” said FSE Director Rosamond Naylor. “Cargill does not support any of our research projects. They support just the base funding…for running the operation.”

Nonetheless, critics like health advocate and journalist Anthony Gucciardi created a Change.org petition titled “Retract the Flawed ‘Organic Study’ Linked to Big Tobacco and Pro-GMO Corps” calling for the retraction of the study and a review of the findings by a third party. This petition currently has over 6,700 signatures.

Further criticism of the meta-analysis method pointed out the link between Olkin and Big Tobacco companies. The petition alleges that Olkin worked with Big Tobacco companies in the past that used meta-analysis to skew data on the health effects of cigarettes. Due to this precedent, the Change.org petition described the meta-analysis method as a “a way to lie with statistics.”

Olkin said he used statistics to investigate studies on the health effects of tobacco for several Big Tobacco companies around 50 years ago. However, he clarified that tobacco companies asked many statisticians to independently evaluate the evidence they found and that his findings did not assert that tobacco was not dangerous.

Other complaints claim that the study failed to address the variety of other benefits that organic food offers consumers such as taste and benefit to the environment.

“Organic food and conventional food may be nutritionally equal and have the same vitamins et cetera, but there are so many other factors at play,” said Head Farmer for the Stanford Farm Project Marika Sitz ’15. “The organic methods are a better way to be environmentally friendly and address the social justice aspect as far as workers rights are concerned.”

The authors of the study countered that from the onset the study’s purpose was not to comment on other potential benefits of organic food but only to decipher whether or not it was healthier than conventional options.

“People choose to consume organic food for many different reasons and this is just one reason,” Smith-Spangler said. “In fact our press release included it and it was included in the introduction and in our abstract and in our conclusion that there are many reasons people may consume organic versus conventional food.”

Organic food supporters such as Sitz still express frustration with the study.

“I would like to see maybe a statement issued by the people who did the study just clarifying some things,” Sitz said.

“We figured the study would definitely get a lot of attention, maybe [it got] a lot more than we ever expected,” Brandeau said, “But we stand by our results.”