Ketosis is a metabolic mechanism for obtaining energy. Normally, the body's preferred source of energy is carbohydrates (sugars). Ketosis is triggered when glucose reserves are depleted, that is, when the body has burned the available sugars, it starts using fat reserves. The burning of fat results in ketone bodies.

Ketosis itself is not diagnostic of any specific condition, but if it appears, the cause must be sought. Fasting, excessive exercise, fever or repeated vomiting can produce ketone bodies, but diabetes, thyroid diseases, certain medications and alcohol intake can also be facilitators.

However, some diets such as keto or ketogenic (hence its name) or those based on prolonged fasting can also produce ketosis. It is unwise to follow these diets with the aim of losing weight, as they can be the beginning of an eating disorder. The recommendation, except in certain cases, is to follow a Mediterranean diet, varied and that includes the continuous consumption of fruits and vegetables as the base of the nutritional pyramid, including carbohydrates, fats and proteins in balanced proportions.