A ketogenic diet is a highly restricted diet that replaces glucose / carbohydrates as the primary fuel in your body with ketones, derived from fats.
Ketogenic diets are often described as having an intake ratio of 65% fat, 30% protein, 5% net carbohydrates (fibre doesn’t count), however the common and rather broad advice for people starting on a ketogenic diet is to restrict net carbohydrates to under 20g/day.
There are similar dietary restriction groups as a traditional mixed diets – standard, carnivore (zero carb), vegetarian and vegan. There are also variations on the ketogenic diet, such as Cyclical Ketogenic Diet (destroys endothelial health, so avoid it) and Targeted Ketogenic Diet (TKD).
For anyone starting on a ketogenic diet, there is more information, including a really neat induction-phase bypass hack inside another article on this website.
Common dietary challenges / deficiencies to watch out for, as an umbrella to the various dietary sub-type specific challenges:
Electrolytes, Vitamin A, Vitamin C