Glossary /
Ketogenesis
The liver's production of ketone bodies from fatty acids when glucose and insulin are low.
What it is
When carbohydrate intake drops and liver glycogen empties — typically after 12 to 36 hours of fasting or several days of a very-low-carb diet — the liver converts fatty acids into three ketone bodies: beta-hydroxybutyrate, acetoacetate, and acetone. The brain, which normally runs on glucose, can derive most of its energy from beta-hydroxybutyrate during ketosis.
Why it matters
Ketones are a clean-burning fuel. They produce fewer reactive oxygen species per unit of ATP than glucose and act as signalling molecules that suppress inflammation and upregulate brain-derived neurotrophic factor (BDNF). This is why ketogenic diets have therapeutic effects in epilepsy and are being studied in Alzheimer’s. For most people the practical value is not living in chronic ketosis but being able to enter it — the metabolic flexibility to switch fuels matters more than the destination.