Por having wanted to alert its readers to the erroneous conclusions that could be drawn from the interpretation of a study with numerous methodological limitations, Point has drawn the wrath of some of his colleagues, who had relayed this work, yet rich in lessons. In order to shed light on the debate, we submitted this study to Denis Corpet, former professor emeritus “Hygiene and Human Nutrition” at the National Veterinary School, in Toulouse, and former director of the INRA “Foods and Cancers” team (laboratory ToxAlim, Toulouse). He is one of the 22 international experts who participated in 2015 in the Working Group on “meat and cancer” at the International Agency for Research on Cancer. Interview.
Point : A study published in January in the Environmental Journal, led by a team of researchers from the departments of nutrition, epidemiology and environmental health at Harvard University, suggests that “the presence of traces of pesticides on fruits and vegetables is likely to cancel out the benefits of their consumption for health “. This result was obtained by following three large epidemiological cohorts of 160,000 Americans. How did the researchers work?
Denis Corpet: It should first be noted that the Harvard team has been working for a very long time, and remains one of the best epidemiology teams in the world. The cohorts on which she bases her work, initially made up of nurses and health personnel, allow for solid analyses. Every four years, their members fill out a self-administered food questionnaire, provide details of their lifestyle, their illnesses, their evolution… Until death. To study the possible effect of pesticide residues on health, the Harvard team had the idea of crossing the data of their cohort with the supposed pesticide content of fruits and vegetables, estimated from another database. of data, maintained by the American administration. They found that people who eat fruits and vegetables known to contain fewer pesticides have a 36% reduction in mortality compared to those who eat more. It is normal that they publish these results. But their study does not cancel what has been demonstrated previously, and repeatedly: that fruits and vegetables are protective, whatever their status!
You mean this study doesn’t prove any particular effects of pesticide residues?
No, this is why their conclusion remains very cautious, in the form of a simple hypothesis: “Our study suggests, they write, that the pesticide content of fruits and vegetables could cancel out the beneficial effect of fruits and vegetables. But this is absolutely not proven.
I understand very well that people who are afraid of pesticides a priori have said to themselves: “I’m stopping eating fruit and vegetables, it’s too dangerous. And it’s really dramatic, because overall French health is going to deteriorate!
What do you mean ?
To quantify the pesticide residue content of different foods, the authors base themselves on statistics established, by sampling, by the American authorities. We know, thanks to this database, that some fruits and vegetables usually contain few pesticides, and others a lot. But their conclusion is not at all obtained from these data, since they did not study pesticides, but the effect of fruits and vegetables! Their data shows that people who eat a certain type of fruit and vegetable (eg lots of peas and oranges) have fewer cancers and cardiovascular disease than those who eat lots of apples, strawberries and spinach. This confirms that some fruits and vegetables are associated with much better protection than others. We already knew it: onions for example, which contain a lot of phyto-nutrients (sulphur compounds), protect much better than potatoes. It is also known that oranges actually protect against stomach cancer, while apples do not. However, in their survey, oranges are in the group of slightly contaminated products, and apples in that of highly contaminated products. But objectively, we do not know if the beneficial effect observed is linked to the lower presence of pesticides, or to the composition of the fruit itself. Their hypothesis is completely unproven.
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What do we know today about the effect of organic food on health?
Very little, actually. It has been observed that farmers who apply or are in direct contact with pesticides suffer more from Parkinson’s disease. But on the general population, there is almost nothing. Epidemiological studies are complex, because the differences observed between organic consumers and others can be attributed to many other factors, organic consumers generally taking better care of their health, they smoke less, do more sport, etc The best study that has been carried out comes from the team of Serge Hercberg, in France, from the Nutrinet cohort, and published under the pen of Julia Baudry. They did not find any effect of organic food, except on one type of cancer, non-Hodgkin’s lymphoma, which is a fairly rare cancer.
Isn’t there a perverse effect in mediating these results without putting them into context?
Reading several daily newspapers, I understand very well that people who are afraid of pesticides a priori have said to themselves: “I’m stopping eating fruit and vegetables, it’s too dangerous. And it’s really dramatic, because overall French health is going to deteriorate! Despite pesticides, fruits and vegetables are globally protective. It’s totally proven! The first message should be that fruits and vegetables protect. Perhaps pesticides slightly reduce this protection, but to date this has not been demonstrated.
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The issue of pesticide residues is omnipresent in public debate. Is it reasonable to worry about it?
Within the Toxalim laboratory, I worked on the links between food and cancer. I chose to study meat and sausages, because their carcinogenic potential seemed to me really worrying. Fifteen years later, thanks in part to our studies, the WHO concluded that cold cuts were carcinogenic, and red meat probably too. But on pesticides, we don’t see anything coming out! Even the best study, that of Julia Baudry that we have cited, released in 2018, only sees an effect on a rare cancer, which has been steadily decreasing since 1990, probably because certain pesticides, in particular organochlorines, have been banned.
Shouldn’t the study by American researchers encourage us to seek more?
Their study is important enough, in any case, for us to decide to give ourselves the means to study, in the United States, the reason why strawberries or spinach have so many pesticide residues, for example. While remembering that strawberry and spinach eaters are doing much better than the others anyway, pesticide residues or not. In France, the standards are not the same, so these results do not concern us.