Ketogenic dietKeto diet

A ketogenic diet restricts carbohydrate far enough that the body shifts towards producing ketone bodies from fat as a major fuel, typically below roughly 50 g of carbohydrate a day, with the remainder of energy coming mostly from fat and moderate protein.

Its best established use is medical rather than aesthetic. Ketogenic diets are an accepted treatment for drug resistant epilepsy, particularly in children, where the evidence goes back a century.

For weight loss it works the way other diets work. Trials matching calories and protein find no metabolic advantage, and the substantial first week loss is glycogen and its associated water rather than fat. Appetite suppression is a genuine and useful feature for some people, which is a real advantage even without a metabolic one.

For metabolic health it can improve glucose control and triglycerides in people with type 2 diabetes, sometimes substantially, and anyone on glucose lowering medication needs medical supervision before starting because doses often have to change.

For performance the pattern is consistent: fat oxidation rises reliably and high intensity performance tends to suffer, partly because carbohydrate use becomes less efficient. That is a poor trade for most training and an acceptable one in some ultra endurance contexts.

Practical costs include an adaptation period of fatigue and headaches, constipation if fibre falls, and the difficulty of eating this way socially over years, which is why adherence rather than physiology usually decides the outcome.

In practice, choose it if the way of eating suits you, expect the adaptation period, do not expect a metabolic edge, and involve a doctor if you take medication for diabetes.