Plant-based diets and the incidence of asthma symptoms in the NutriNet-Santé cohort

Plant-based diets have been shown to be associated with a reduction of the risk of noncommunicable diseases, but not all plant foods have health benefits. A lower incidence of asthma has been reported in older women for both healthy (hPDI) and unhealthy (uPDI) plant-based diets, but these associations need to be confirmed in younger populations and men. We aim to examine the association between plant-based diet indices and the incidence of asthma in the French NutriNet-Santé cohort, considering body mass index (BMI) as a mediator. We included 19,612 NutriNet-Santé participants (26% men; mean age: 54.8 years (sd:13)) who completed respiratory surveys in 2016 and 2020 and provided repeated 24-hour dietary records within the first two years of follow-up (2009-2013). The nutritional quality of a plant-based diet was assessed using the hPDI and uPDI diet scores. The incidence of asthma symptoms was defined as the onset of symptoms by 2020 in asymptomatic participants in 2016. Mediation analyses using the counterfactual approach were conducted to breakdown the total, direct, and indirect (mediated through BMI) effects of plant-based diets (continuous) on asthma symptoms incidence. After adjustment for confounders, the hPDI was significantly associated with a lower asthma symptoms incidence only through an indirect effect mediated by BMI (OR=0.97; 95%CI=0.96-0.98), and no significant direct effect was observed (OR=1.03, 95% CI=0.98-1.08). Conversely, uPDI was not associated with asthma symptoms incidence, either directly or indirectly. Adherence to a healthful plant-based diet may be associated with a reduced risk incidence of asthma, mainly through mediation by BMI.