HCAR2 and allergic asthma: Ketone bodies can modulate several of the key pathologic processes involved in both obese and allergic asthma.16, 17, 18 As an energy source, ketone bodies make cells less reliant on glycolysis,14,19, 20, 21, 22, 23 as a result of which they produce less lactic acid, a catabolite implicated as a causal factor in the pathogenesis of allergic asthma.24, 25, 26, 27, 28 Ketone bodies have been reported to function through cell surface receptors, including the G protein–coupled receptors hydroxycarboxylic acid receptor 2 (HCAR2/GPR109a) and free fatty acid receptor 3 (FFAR3/GPR41).11