Revisiting the thrifty substrate hypothesis: Ketone bodies as cardioprotective fuels in diabetes and SGLT2 inhibitor therapy.

SGLT2 inhibitors increase circulating β-hydroxybutyrate (β-OH-B), a ketone body that may enhance cardiac efficiency in HFrEF. The "thrifty substrate hypothesis" suggests β-OH-B provides more ATP per oxygen consumed than glucose or fatty acids. Clinical studies by Nielsen et al. and Solis-Herrera et al. show that β-OH-B infusion improves cardiac output, ejection fraction, and myocardial blood flow in HFrEF patients-with and without diabetes-without increasing oxygen demand or reducing glucose uptake. These findings support β-OH-B as an additive metabolic fuel, highlighting the therapeutic potential of enhancing cardiac metabolic flexibility.