Ketosis is a natural metabolic state in which the body uses fat rather than carbohydrates as its primary source of energy.

Normally, the body breaks down carbohydrates into glucose, which is then used to fuel cells.

When carbohydrate intake becomes very low—because of fasting, prolonged exercise, or a low-carbohydrate diet—the body’s glucose supply drops.

To meet energy needs, the liver begins converting fats into small molecules called ketone bodies, including beta-hydroxybutyrate, acetoacetate, and acetone.

These ketones circulate in the bloodstream and provide energy to tissues, especially the brain, which cannot use fat directly.

Achieving ketosis usually requires significantly reducing daily carbohydrate intake while increasing consumption of fats and moderate protein.

This triggers hormonal changes that encourage fat breakdown.

People often measure ketone levels in blood, breath, or urine to confirm they are in ketosis.

Many individuals enter ketosis intentionally for dietary purposes.

The ketogenic diet, which is high in fat, moderate in protein, and very low in carbohydrates, is commonly used for weight loss because fat burning increases.

Ketosis may also help stabilise blood sugar, reduce hunger, and improve insulin sensitivity.

Medically, ketogenic diets have been used to help manage epilepsy, particularly in children who do not respond well to medication.

Research continues into possible benefits for metabolic disorders, neurodegenerative diseases, and mental health.

While generally safe for many people, ketosis can produce temporary side effects, often called the “keto flu”: fatigue, headache, irritability, or digestive changes.

These symptoms usually fade as the body adapts.

Severe complications like ketoacidosis are different and occur mainly in people with uncontrolled diabetes.

Overall, ketosis is a well-studied metabolic state that reflects the body’s ability to switch fuel sources, emphasizing fat-derived ketones instead of glucose.