Human body can obtain energy from either carbohydrate or fat digestion. Although glucose metabolism derived from carbohydrate-based diets has long been utilized for energy supply, it has been recently discovered that shifting from glucose to fatty acid metabolism may become a novel way for improving human health especially when carbohydrate is deprived. In recent years, intermittent fasting and ketogenic diets have received a lot of attention in respect to favoring fatty acid metabolism. In all cases, fatty acid metabolism produces D-β-hydroxybutyrate (D3HB), which is a natural ketone body, as well as, a monomer of microbial poly-D-β-hydroxybutyrate (PHB). D3HB can be utilized by different cells of the body as an alternative energy fuel or an intracellular signaling molecule with multiple downstream signaling pathways. Usually, the serum level of D3HB is increased during ketogenic diets, however, requires a very long period of adaptation (over 3-months) and exhibits unwanted adverse effects. Hence, exogenous ketone supplements using D3HB have become a more effective approach to induce and maintain nutritional ketosis for subsequent functional effects. This review describes how D3HB is produced and metabolized within the body, the functional roles played by D3HB, and a detailed summary of the different applications of exogenous ketones that have been explored to date in both nutritional and therapeutical context.
Keywords: D-β-hydroxybutyrate; D3HB; PHB; biosynthesis; exogenous ketones; ketone metabolism; nutritional ketosis.