BHB is the main ketone body produced by the liver via the breakdown of fatty acids. One study found that BHB crosses the blood-brain barrier and the levels of BHB in the brain actually increased by more than ten times after following a severely calorie restricted diet. More and more research is coming out now showing the multifaceted benefits of BHB beyond just being a superior source of fuel for the brain.
Stubbs BJ, Cox PJ, Evans RD, et al. On the Metabolism of Exogenous Ketones in Humans. Front Physiol. 2017;8:848. Published 2017 Oct 30. doi:10.3389/fphys.2017.00848.