What Is Ketosis?
Ketosis is a metabolic state in which your body burns fat for fuel instead of glucose, producing molecules called ketones. It's triggered by significantly cutting carbohydrate intake — typically below 20-50 grams of net carbs per day.
When carbohydrate intake drops low enough, your liver starts converting fat into ketones — small energy molecules that fuel your brain and muscles in place of glucose. This shift is the foundation of the ketogenic diet, but it can also occur during extended fasting once glycogen stores are depleted. Doctors define nutritional ketosis as blood ketone levels between 0.5 and 3.0 mmol/L, measurable through blood, breath, or urine tests. Most people reach this state within two to seven days of consistently eating under 20 grams of net carbs daily, though the timeline varies with activity level and individual metabolism.