Ketosis is a metabolic state in which the body switches from glucose to fat and starts running on ketone bodies. In the liver, three ketone bodies are formed from fatty acids: beta-hydroxybutyrate (BHB), acetoacetate and acetone.
Ketosis develops when carbohydrates are scarce — during fasting, a ketogenic diet or prolonged exercise. Usually this requires getting fewer than about 50 g of carbohydrates a day for several days.
Nutritional ketosis and its markers
In the normal state the blood ketone level is below 0.5 mmol/L. In nutritional (physiological) ketosis the beta-hydroxybutyrate concentration rises to about 0.5–3 mmol/L. Ketosis can be measured by blood (most accurately — BHB), by breath (acetone) or by urine (less reliable). This is a controlled state, safe for a healthy person.
Ketosis versus ketoacidosis
It is important not to confuse nutritional ketosis with diabetic ketoacidosis. In ketoacidosis the ketone level exceeds ~10 mmol/L and the blood's acid-base balance shifts — a life-threatening complication, more often in diabetes with insulin deficiency. Physiological ketosis, by contrast, keeps the blood pH normal.
Why ketosis is used
The ketogenic diet has long and reliably been used to treat drug-resistant epilepsy. There is interest in its role in metabolic syndrome, type 2 diabetes and weight loss. But long-term data are still mixed, and strict restrictions do not suit everyone — so such diets are best used deliberately, and in the presence of disease, under a doctor's supervision.
Calculate using this marker
Calculators where Ketosis is used directly:
Frequently asked questions
Is ketosis the same as ketoacidosis?
No. Nutritional ketosis is safe and keeps ketones roughly within 0.5–3 mmol/L at normal pH. Ketoacidosis is >10 mmol/L with a shift in blood acidity, a dangerous condition.
How do I know I am in ketosis?
Most accurately — measure beta-hydroxybutyrate in the blood (the nutritional-ketosis guide is 0.5–3 mmol/L). Urine test strips and breath acetone analysers are also used.