Ketones are important metabolites produced by the liver that increase when carbohydrates are limited in the diet. Thus, very low-carbohydrate diets are often called ketogenic diets because they result in a significant increase in blood levels of ketones. Ketones serve as an alternative fuel when glucose (derived from carbohydrate in the diet) is scarce. Even the brain, which normally depends on a steady supply of glucose, can use ketones for fuel. Since ketones are simply derived from fatty acids stored in fat cells, accelerated ketone production indicates that fat stores are being mobilized (burned for energy). Thus, being in ketosis is a favorable metabolic state to be in for people wanting to lose body fat. But new research has cast a whole new light on ketones extending their role beyond simply an auxiliary fuel source.
A water-shed paper recently published in ‘Science’ reported that the primary circulating ketone (ß-hydroxybutyrate or BOHB) is a potent regulator of a group of genes that protect cells from oxidative stress.
Two subsequent studies showed that ketones are longevity metabolites. One study showed that elevated ketone levels extended life span by 26% in worms, and the other showed that ketones corrected the metabolic defects in a mouse model of accelerated aging. For humans to produce ketones, you would need to reduce your carb intake to about 50 grams per day or less, not including fiber carbs. This exciting new perspective on ketones as both a fuel source and cell signaling molecule might open the door to exciting new therapeutic discoveries related to a ketogenic diet.

Reference: Science. 2013 Jan 11;339(6116):211-4. Aging (Albany NY). 2014 Aug;6(8):621-44. Cell Metab. 2014 Nov 4;20(5):840-55.

Jeff S. Volek is a registered dietitian and Full Professor in the Department of Human Sciences at The Ohio State University. He has published 270 articles examining health and performance effects of low-carbohydrate diets and other dietary supplements including seminal work on creatine, carnitine and whey protein.