Innate lymphoid cells (ILCs) play an important role in the control and maintenance of barrier immunity. However, chronic activation of ILCs results in immune-mediated pathology. Here, we show that tissue-resident type 2 ILCs (ILC2s) display a distinct metabolic signature upon chronic activation. In the context of allergen-driven airway inflammation, ILC2s increase their uptake of both external lipids and glucose. Externally acquired fatty acids are transiently stored in lipid droplets and converted into phospholipids to promote the proliferation of ILC2s. This metabolic program is imprinted by interleukin-33 (IL-33) and regulated by the genes Pparg and Dgat1, which are both controlled by glucose availability and mTOR signaling. Restricting dietary glucose by feeding mice a ketogenic diet largely ablated ILC2-mediated airway inflammation by impairing fatty acid metabolism and the formation of lipid droplets. Together, these results reveal that pathogenic ILC2 responses require lipid metabolism and identify ketogenic diet as a potent intervention strategy to treat airway inflammation. Display omitted •ILC2s take up external lipids, which are transiently stored in lipid droplets•External lipids are converted into phospholipids to promote the proliferation of ILC2s•PPARγ and DGAT1 control lipid uptake and transient storage in lipid droplets•Ketogenic diet prevents ILC2-driven airway inflammation Type 2 innate lymphoid cells (ILC2s) are contributing to the development of airway inflammation upon chronic activation. Karagiannis and colleagues reveal that external lipids transiently stored in lipid droplets are required to fuel pathogenic ILC2 responses and identify a ketogenic diet as a potent intervention strategy to treat ILC2-driven airway inflammation.