Ketosis
A metabolic state in which the body, in the absence of carbohydrate, makes ketones from fat to fuel its cells.
Normally, the body uses glucose as fuel. With severe carbohydrate restriction (< 50 g/day) or prolonged fasting, the liver makes ketone bodies (acetoacetate, beta-hydroxybutyrate, acetone) from fatty acids. These ketones become the main fuel for the brain and muscles.
Entering ketosis generally takes 3-7 days of very low carbohydrate intake. The degree (mild vs deep) varies with the individual, the time elapsed and physical activity.
Documented benefits: rapid weight loss (mostly water at first), appetite suppression, improved mental energy (for some) and blood sugar stability in people with type 2 diabetes.
A fresh angle (rarely highlighted): ketosis is NOT diabetic ketoacidosis, a dangerous condition in uncontrolled diabetics. Nutritional ketosis is physiological and safe in healthy people.
But BEWARE: entering or leaving ketosis quickly can cause the “keto flu” (fatigue, headaches, nausea) as the body adapts. Some people love it (clear energy), others hate it (fatigue, low mood). It is very individual.
One last point: ketosis reduces some aspects of muscular performance (raw strength) compared with a carbohydrate-rich diet. For athletes, it is a trade-off: weight loss and mental clarity versus reduced explosive capacity.