Pesticides are used in conventional agriculture to control pests, weeds and pathogens in order to reduce yield losses and post-harvest and storage losses. The use of pesticides is continuously increasing worldwide. According to the Food and Agriculture Organisation of the United Nations (FAO), around 3.70 million tonnes of pesticides were used in agriculture worldwide in 2022. This corresponds to an increase of 4% compared to 2021 [1]. At the same time, there are more overweight and obese people worldwide than ever before. According to current forecasts, around 38% of the world's population will be overweight and a further 20% obese by 2030. This will be accompanied by an increase in numerous associated diseases such as type 2 diabetes, cardiovascular diseases, various types of cancer and infertility.

Until now, genetic and lifestyle-related factors were considered to be the main causes of weight gain. Increasingly, however, the influence of environmental factors such as pesticides is also being recognised. The chemically synthesised molecules interfere with the human metabolism and mimic hormones, which can lead to dysregulation of the thyroid gland and fertility problems, for example. These effects have a different impact on men and women due to sex-specific differences in metabolic regulation. It has also been shown that pesticides change the activity of fat cells and influence the regulation of hunger and satiety. Pesticides or their derivatives are absorbed through the air, drinking water and above all through food. There are already studies that have found a change in body weight in farmers in connection with chronic occupational exposure to pesticides [2]. However, little research has been conducted into how such pesticide exposure affects body weight in the general population. Berlivet et al (2024) therefore investigated the role of dietary pesticide exposure in body weight change as part of the NutriNet-Santé study, focussing on possible sex-specific differences [3].

Study design

The dietary data came from France from the large-scale prospective cohort study NutriNet-Santé on the relationship between diet and health. The participants completed a validated questionnaire on the frequency of consumption of organic and conventional foods in 2014. On this basis, the researchers calculated the amount of plant-based food consumed and the resulting pesticide exposure.

The data on the contamination of the plant-based foods came from the European Reference Laboratory for Pesticides (Chemical and Veterinary Investigation Centre Stuttgart (CVUAS)). The database contains over 6.7 million combinations of foods and pesticides, including organic products. A total of 25 pesticides were selected that occur frequently in Europe, three of which are authorised in organic farming (azadirachtin, pyrethrin and spinosad), see Table 1. The profiles of dietary pesticide exposure were derived on the basis of individual eating habits. The researchers used a special mathematical method called non-negative matrix factorisation (NMF) for this purpose. This is used to structure and simplify complex data sets. A total of four main components (NMF profiles) were identified, each representing clusters of commonly occurring pesticides in the participants' diets:

NMF1: Exposure to synthetic pesticides: strong correlations with chlorpyrifos, imazalil, malathion, profenofos and thiabendazole.
NMF2: Exposure to synthetic pesticides: strong correlations with azoxystrobin, boscalid, cyprodinil, chlorpropham, difenoconazole, fenhexamid, iprodione, tebuconazole and lambda-cyhalothrin.
NMF3: Exposure to naturally occurring active substances: strong correlations with spinosad and azadirachtin.
NMF4: Exposure to synthetic pesticides: strong correlations with acetamiprid, carbendazim, cypermethrin and dimethoate/methoate. 

Table 1: Occurrence of individual active ingredients of pesticides in the NMF clusters (correlations for 32,062 data sets)

To collect the body weight data, the participants answered an anthropometric questionnaire every six months from 2014 to 2021. In addition, socio-demographic characteristics and lifestyle factors were recorded. People who, for example, only had a single weight measurement during the follow-up, were on a diet or became pregnant during the study were excluded. In total, the data from 32,062 participants was analysed. Of these, 74% were women with an average age of 52.9 years. The men were on average 58.5 years old.

Results

At the beginning of the study, the average body mass index was 23.9 kg/m² regardless of sex, which corresponds to a normal weight. Over the course of the observation period, postmenopausal women and men lost weight slightly (approx. -0.03 kg/year and approx. -0.05 kg/year respectively), while premenopausal women gained weight (approx.+ 0.32 kg/year). The results for men and premenopausal women were significant.

For NMF2 (exposure to synthetic pesticides, see Table 1), there was a significant negative correlation with body weight in men: the higher the exposure and thus the consumption of conventional foods, the greater the average weight loss of approx. 0.05 kg/year.

There was no significant effect in the overall group of women. It was also shown that a higher exposure to natural active ingredients (NMF3) - which suggests a higher consumption of organic food - was associated with a lower weight gain. Premenopausal women in particular gained an average of approx. 0.04 kg less per year than women who were less exposed, although this was not significant. No significant correlation was found in men either.

In the case of increased exposure to synthetic pesticides from NMF1 and NMF4, there was no significant correlation with weight development over time in either sex.

These results remained stable even after adjustment for missing data – for example on fruit and vegetable consumption, fat and fibre intake.

To summarise: During the observation period, men lost a significant amount of weight and women tended to lose weight after the menopause, while women before the menopause gained a significant amount of weight on average. Women who were more exposed to NMF3 – a sign of less contact with synthetic pesticides and higher consumption of organic food - gained less weight, especially the premenopausal women. In men, greater weight loss was observed when they were exposed to higher levels of synthetic pesticides (NMF2). In women, however, NMF2 had no measurable effect on weight in the overall group. No correlation with body weight was found for NMF1 and NMF4.

Discussion

It is undisputed that pesticides are harmful – both to the environment and to human health. Although food may only be marketed if the pesticide limits are complied with, this study illustrates that there are indeed health effects on humans even at low concentrations, especially over a longer period of time. Various analyses of the data from the NutriNet study have already demonstrated this [4]. In the present analysis, the weight changes are striking, although they were not uniform and only partially significant. The researchers attribute the difference to the older age of the men and the different hormonal status of the women. Hormonally sensitive groups in particular, such as premenopausal women, appear to react more strongly to pesticide residues. Although the weight changes per year were small in each case and there are also many factors that can influence weight, it is possible to speak of an overall trend, as it is evident in a large cohort (over 32,000 study participants) and therefore has a certain relevance. Since the change in weight was also observed annually, the effect adds up and still results in a significant decrease or increase over time. It would be interesting to investigate the influence of pesticides on body weight in further studies in order to better understand the development of being overweight and obesity.

What becomes clear are not only the short-term, but also the long-term negative effects of pesticide residues in food, which were observed over a period of seven years. These even appear to overshadow the actual health-promoting effects of foods such as vegetables. Vegetables are a central component of a healthy diet – but as the study shows, the consumption of vegetables with pesticide residues, even if they are within the limit values, leads to a change in metabolism and thus to a change in weight.

Organic and biodynamically produced food is not generally completely pesticide-free – for example, copper compounds, sulphur or the active ingredient spinosad, which was considered in the study, may be used – but their use is strictly limited and regulated. Biodynamics follows the principle that agriculture is possible without pesticides. This requires comprehensive management, for example in soil cultivation, the choice of plant varieties, fertilisation and crop rotation. If all these aspects and others such as local cultivation, weather and climate conditions are taken into account, the use of pesticides can be significantly reduced or even eliminated. This will result in food that can truly unfold its health-promoting effects and thus contribute to the health of people and the planet.

Bibliography

[1] FAO (2024): "Pesticides use and trade - 1990-2022" FAOSTAT Analytical Briefs, 89.13
doi.org/10.4060/cd1486endoi.org/10.4060/cd1486en

[2] Araújo RAL, Cremonese C, Santos R, Piccoli C, Carvalho G, Freire C, Canut R (2021): "Association of occupational exposure to pesticides with overweight and abdominal obesity in family farmers in southern Brazil" International Journal of Environmental Health Research, 32(12), 2798-2809. doi.org/10.1080/09603123.2021.1991284

[3] Berlivet J, Payrastre L, Rebouillat P, Fougerat A, Touvier M, Hercberg S, Lairon D, Pointereau P, Guillou H, Vidal R, Baudry J, Kesse-Guyot E (2024): "Association between dietary pesticide exposure profiles and body weight change in French adults: Results from the NutriNet-Santé" Environment International, 184(108485), 0160-4120. doi.org/10.1016/j.envint.2024.108485

[4] Baudry J, Assmann KE, Touvier M, et al. Association of frequency of organic food consumption with cancer risk: findings from the NutriNet-Santé prospective cohort study. JAMA Intern Med. 2018;178(12):1597-1606. https://doi:10.1001/jamainternmed.2018.4357