Low-carbohydrate diets or low-carb diets are dietary programs that restrict carbohydrate consumption usually for weight control. Foods high in digestible carbohydrates are limited or replaced with foods containing a higher percentage of proteins and fats.

The precise definition of low-carbohydrate diets varies greatly. The term is most commonly used to refer to ketogenic diets, i.e. diets that restrict carbohydrate intake sufficiently to cause ketosis like the Atkins diet, but some sources consider less restrictive variants to be low-carbohydrate as well.

Apart from obesity low-carbohydrate diets are often discussed as treatments for some other conditions, most notably diabetes and epilepsy, although these treatments still remain controversial and lack widespread support.