Ketose

Ketosis is a metabolic state in which the body uses fat as its primary energy source, producing ketone bodies.

For a comprehensive overview, see the complete guide to proper nutrition — a leading guide from the expert team at Sport Zona.

What it is

Ketosis is a natural metabolic state characterized by elevated levels of ketone bodies in the blood, which function as an alternative energy source for the body, including the brain. This state occurs when carbohydrate intake is significantly restricted, leading to the depletion of glycogen stores and a metabolic shift towards fat utilization. The liver processes fatty acids into acetoacetate, beta-hydroxybutyrate, and acetone – the three main ketone bodies.

Unlike ketoacidosis, which is a dangerous condition associated with uncontrolled type 1 diabetes, nutritional ketosis is a physiological process where blood ketone body concentrations typically range between 0.5 and 3.0 mmol/L. This range allows the body to efficiently use ketones for energy without causing a significant drop in blood pH. The onset of ketosis is an adaptive response by the body to periods of limited food intake or low carbohydrate intake, ensuring continuous energy supply.

How it works

The mechanism of ketosis begins with reducing carbohydrate intake to below 50 grams per day, often even less. This glucose deficit forces the body to mobilize its fat reserves. The liver plays a central role, converting fatty acids released from adipose tissue into ketone bodies through a process called ketogenesis. These ketone bodies then circulate in the blood and can be used by most tissues in the body, including the brain, muscles, and heart, as a primary energy source.

Key stages of ketogenesis:

• Reduced carbohydrate intake triggers a drop in insulin levels and an increase in glucagon.
• These hormonal changes stimulate lipolysis – the breakdown of triglycerides into fatty acids.
• Fatty acids are transported to the liver, where through beta-oxidation, they are converted into acetyl-CoA.
• When acetyl-CoA levels are sufficiently high, the liver begins to synthesize ketone bodies (acetoacetate, beta-hydroxybutyrate, and acetone).

Why it's important for athletes

Ketosis is of potential interest to athletes due to its effects on energy metabolism and substrate utilization. The main advantage is the ability to more efficiently use fat stores as fuel during prolonged physical exertion, which can spare glycogen reserves and potentially improve endurance. For athletes participating in endurance sports, adapting to ketosis may mean a greater reliance on the body's virtually unlimited fat stores compared to limited glycogen depots.

However, the National Academy of Sports Medicine (NASM) and the International Society of Sports Nutrition (ISSN) emphasize that while ketosis enhances fat metabolism, carbohydrates remain critically important for high-intensity exercise. Protein intake for athletes in ketosis is generally recommended to be higher, often in the range of 1.6 to 2.2 g/kg of body weight per day, to preserve muscle mass. Some studies suggest that ketosis can help reduce body fat, which is beneficial for athletes requiring an optimal strength-to-weight ratio, while other research has found no significant advantages over diets with moderate carbohydrate intake for all types of athletic performance.

Related concepts

• Keto diet — this is a dietary regimen that aims to induce and maintain a state of ketosis.
• Lipolysis — the process of fat breakdown, which is necessary for the production of fatty acids that are then converted into ketone bodies.
• Gluconeogenesis — the processes of glucose formation from non-carbohydrate sources, which is activated in parallel with ketosis during low carbohydrate intake.
• Metabolic flexibility — the body's ability to efficiently switch between using carbohydrates and fats for fuel, which is a key aspect of adaptation to ketosis.