Recent years have highlighted the close correlation between obesity and asthma. Most studies concluded that obesity is a risk factor for the development of asthma, increases asthma severity, and induces a weaker responsiveness to medication including corticosteroids. In contrast, overweight, as opposed to obesity, may exert beneficial health effects and has been associated with reduced all-cause mortality or chronic obstructive pulmonary disease. However, the majority of studies dealing with the impact of bodyweight increase on asthma development include subjects with a BMI ≥ 85% percentile, which does not distinguish between overweight and obesity. Thus, the effect of overweight in comparison to normal weight or obesity on the development of allergic asthma is still ill-defined.

In experimental models, the impact of genetically- or dietary-induced bodyweight increase on allergic asthma development has been reported. However, such studies showed heterogeneous effects on asthma development, in particular on airway hyperresponsiveness, eosinophilia, and adaptive immune responses.

In a new study published in Clinical and Experimental Allergy, researchers from the Laumonnier and Köhl labs at the Institute for Systemic Inflammation Research, in collaboration with the Senad lab at Cincinnati Children's Hospital, found that in contrast to obesity, a mild bodyweight gain protects from the development and severity of experimental allergic asthma.

In a mouse model of ovalbumin-induced experimental allergic asthma, mice were fed with high fat diet (HFD) resulting in mild bodyweight gain, associated with mild metabolic alterations. Interestingly, the metabolic perturbations decreased methacholine-induced airway hyperresponsiveness and airway inflammation. Furthermore, the decrease in the allergic phenotype was associated with decreased numbers of pulmonary conventional DCs (cDC) and monocyte-derived DCs (moDC), lower expression of MHC II and CD40 in such cDCs and a decreased frequency of IFN+and IL-17+but not IL-13+CD44+T effector cells. 

The new findings point towards a complex functional link between metabolism and the development of pulmonary allergy and suggests that mild bodyweight have protective effect in allergic asthma development. In future studies, it remains to be shown whether this protective effects also applies to carefully stratified overweight humans.