When carbohydrate intake falls below roughly 20–50 g per day and liver glycogen depletes, the liver converts fatty acids into ketone bodies — acetoacetate, beta-hydroxybutyrate, and acetone. Tissues including the brain shift to using these ketones as fuel instead of glucose.
Nutritional ketosis (achieved through a ketogenic diet) is distinct from diabetic ketoacidosis, a dangerous condition in people with insulin-dependent diabetes where both ketones and blood glucose are severely elevated.
The ketogenic diet has strong evidence for refractory epilepsy and is used therapeutically. For weight loss, it can be effective in the short to medium term — largely through reduced appetite and overall calorie intake — but is not superior to other well-structured approaches over the long term. Adherence is the main limiting factor. For an Indian dietary context, see the Indian keto diet guide. If you have diabetes or take blood-glucose-lowering medication, discuss any very-low-carbohydrate diet with your clinician first.