Low-carbohydrate diets or low-carb diets are dietary programs that restrict carbohydrate consumption usually for weight control or for the treatment of obesity. Foods high in digestible carbohydrates (e.g. breads, pasta) are limited or replaced with foods containing a higher percentage of proteins and fats (e.g. meats, soy products) and often other foods low in carbohydrates (e.g. green leafy vegetables).

The American Academy of Family Physicians provides the following definition of low-carbohydrate diets.

Low-carbohydrate diets restrict caloric intake by reducing the consumption of carbohydrates to 20 to 60 g per day (typically less than 20 percent of the daily caloric intake). The consumption of protein and fat is increased to compensate for part of the calories that formerly came from carbohydrates.

This definition is typical of most sources although no universally recognized definition has been established. Such diets are generally ketogenic (i.e. they restrict carbohydrate intake sufficiently to cause ketosis) for example, the induction phase of the Atkins diet. Some sources, though, consider less restrictive variants to be low-carbohydrate as well.

The ketogenic diet is a high fat, adequate protein, low-carbohydrate diet, primarily used to treat difficult-to-control epilepsy in children. It is stricter than most low-carbohydrate diets, and must be followed under close medical supervision. The use of a ketogenic diet to treat other medical conditions remains at early research stages.

Beginnings

Some anthropologists believe that early humans were hunter-gatherers consuming diets high in both protein and fat and mostly low in nutritive carbohydrates (although their diets would have been high in fiber). Indeed some isolated societies exist still today which continue to consume these types of diets. The advent of agriculture brought about the rise of civilization and the gradual rise of carbohydrate levels in human diets. The modern age has seen a particularly steep rise in refined carbohydrate levels in so-called Western societies.

In 1863 William Banting, an obese English undertaker and coffin maker, published "Letter on Corpulence Addressed to the Public" in which he described a diet for weight control giving up bread, butter, milk, sugar, beer and potatoes. His booklet was widely read, so much so that some people used the term "Banting" for the activity usually called "dieting." .

In 1967, Dr. Irwin Stillman published The Doctor's Quick Weight Loss Diet. The "Stillman Diet" is a high-protein, low-carbohydrate and low-fat diet. It is regarded as one of the first low-carbohydrate diets to become popular in the US. Other low-carbohydrate diets in the 1960s included Air Force Diet and the Drinking Man's Diet. Austrian physician Dr Wolfgang Lutz published his book 'Leben Ohne Brot' (Life Without Bread) in 1967. However it was hardly noticed in the English speaking world.