β-hydroxybutyrate (βOHB), ketone body is produced during a prolonged low-caloric or ketonic diet.

Low concentrations of βOHB helps protect cells from "oxidative stress". dietary restriction (DR) spurs βOHB production. βOHB is an endogenous and specific inhibitor of class I histone deacetylases (HDACs). Exogenous βOHB administration, fasting or DR increases global histone acetylation in mouse tissues. HDAC inhibition by βOHB is correlated with global changes in transcription, including oxidative stress factors Foxo3a and Mt2. Cells treated with βOHB have increased histone acetylation at Foxo3a and Mt2 promoters. Both Foxo3a and Mt2 are activated by selective depletion of HDAC1 and HDAC2. normally keeps a pair of genes, namely Foxo3a and Mt2 switched off [http://www.biocompare.com/Life-Science-News/126847-Gladstone-Scientists-Discover-Novel-Mechanism-By-Which-Calorie-Restriction-Influences-Longevity/; http://www.sciencemag.org/content/early/2012/12/05/science.1227166].