What happens as glycogen empties and fat oxidation rises
When carbohydrate intake drops low, often cited near 50 grams per day or below, the body's glycogen stores draw down over roughly the first few days. As circulating glucose and insulin fall, the liver increases fat breakdown and begins converting fatty acids into ketone bodies, which tissues including the brain can use for fuel. Blood ketones commonly climb into a range of about 0.5 to 3 mmol/L in nutritional ketosis.
The exact threshold and timeline vary between individuals based on activity, prior diet, and total energy intake, so these figures are typical rather than universal.
The adjustment period and who should be cautious
Early in the transition some people experience fatigue, headache, or reduced exercise capacity, sometimes called the keto adaptation phase, often easing over one to several weeks. Adequate fluid and electrolytes are frequently emphasized during this period because water and sodium losses can rise.
This is general educational information, not medical advice. Ketogenic diets are not appropriate for everyone and can be unsafe for people with certain conditions or on certain medications, including some diabetes drugs; consult a qualified professional before starting.