Does organic eating reduce the risk of cancer? Hard to prove

A large study published Monday showing that the biggest French eaters of organic food had fewer cancers than those who never ate it illustrates the difficulty of establishing a cause-and-effect relationship between diet and health.

It is impossible to categorically prove in the laboratory that such a food reduces the risk of a disease as complex as cancer.

Researchers must therefore follow a large number of people and wait for cancers to develop in some, hoping to isolate posteriori patient-specific behavior.

Thousands of studies on diet and various diseases have been conducted for decades. Even the biggest are sometimes disputed, such as the famous experiment that showed in 2013 the beneficial effects of the Mediterranean diet against heart disease, but was removed from a prestigious medical journal this year, because of methodological problems.

Regarding bio, only one large study had previously looked at the effect on cancer, the Million Women Study, with 600,000 British women (2014). She found no difference between organic consumers and non-users on the overall risk of cancer, but had seen a reduced risk for a particular cancer: non-Hodgkin's lymphoma.

The French study (Sorbonne, Inra, Inserm …) is more detailed, although it has fewer participants, about 69,000, mostly women. His results are published in the American magazine Jama.

The hypothesis is that organic consumers ingest less synthetic pesticides from fruits, vegetables or cereals, and thus reduce their risk, as some pesticides are suspected of being carcinogenic.

After their recruitment, the volunteers of the NutriNet-Santé study completed a questionnaire (income, physical activity, smoker or not, body mbad index …) and declared the organic food consumed in the previous 24 hours.

The study divided participants into four groups, according to their bio consumption. Then the number of cancers in each group was counted, over four and a half years on average.

In the quarter of people who reported eating the most organic, the risk of cancer was 25% lower than in the quarter who never ate it. In absolute terms, the increase is only 0.6 points, ie six additional patients per 1,000 people.

– "Complex" –

The study found a statistically significant correlation only for bad cancer for postmenopausal women, and for lymphoma including non-Hodgkin's lymphoma.

The authors took care to correct their results to take into account that organic eaters were, on average, richer, less obese, less smokers.

But other invisible factors, environmental or lifestyle-related, may also play a role.

This is the typical problem of these studies.

"People who eat organic deliberately, to the point of declaring it, are probably different from others in many other ways," says AFP Nigel Brockton, director of research at the American Institute for Research Against Cancer ( AICR).

He recommends, rather than a particular type of food, a set of practices to reduce the risks of cancer: normal weight, physical activity, healthy diet, not too much red meat …

"The diet is a complex thing," he says. "We would never make a recommendation based on a single study, even if it is statistically significant."

Other problems were noted: pesticide traces in the participants were not measured, which led to Harvard expert criticism in the same issue of Jama. Co-author Julia Baudry told AFP that this was done only on a small subsample.

The declarative aspect is also a problem for John Ioannidis, professor emeritus of medicine at Stanford, who is known to have stated that most of the published studies were false.

"Most people, including myself, would be unable to say exactly how much organic food they eat," he told AFP. "The study is 3% lucky to have found something important, and 97% to propagate absurd and ridiculous results," he concludes.

But "research advances one study at a time," says Dr. Brockton.

As for red meat or cigarettes, it will take many studies going in the same direction to conclude on organic food.

In the meantime, the American Cancer Society continues to advocate eating fruits and vegetables, organic or not.