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. bread, pasta) are limited or replaced with foods containing a higher percentage of proteins and fats (e.g., meat, 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.
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.
Apart from obesity, low-carbohydrate diets are often discussed as treatments for some other conditions, most notably diabetes and epilepsy, although, other than for intractable epilepsy in children, these treatments still remain controversial and lack widespread support.
History
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 today which 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 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.
In 1972, Dr. Robert Atkins published Dr. Atkins Diet Revolution which advocated a low-carbohydrate diet he had successfully used in treating patients in the 1960s (having himself developed the diet from an unspecified article published in JAMA). The book met with some success but, because of research at that time suggesting risk factors associated with excess fat and protein, it was widely criticized by the mainstream medical community as being dangerous and misleading, thereby limiting its appeal at the time. Among other things critics pointed out that Dr. Atkins had done little real research into his theories and based them mostly on anecdotal evidence. Later that decade, Walter Voegtlin and Dr. Herman Tarnower published books advocating the Stone age diet and Scarsdale diet, respectively, each meeting with moderate success.
The concept of the glycemic index was invented in 1981 by Dr. David Jenkins. This concept evaluates foods according to their effect on blood sugar levels—with fast digesting simple carbohydrates causing a sharper increase and slower digesting complex carbohydrates such as whole grains a shallower one.
Low-carb diets since the 1990s
In the 1990s Dr. Atkins published Dr. Atkins New Diet Revolution and other doctors began to publish books based on the same principles. This has been said to be the beginning of the "low carb craze." During the late 1990s and early 2000s low-carbohydrate diets became some of the most popular diets in the U.S. (by some accounts as much as 18% of the population was using a low-carbohydrate diet at its peak) and spread to many countries. These were noted by some food manufacturers and restaurant chains as substantially affecting their businesses (notably Krispy Kreme). This was in spite of the fact that the mainstream medical community continued to denounce low-carbohydrate diets as being a dangerous trend. It is, however, valuable to note that many of these same doctors and institutions at the same time quietly began altering their own advice to be closer to the low-carbohydrate recommendations (e.g. eating more protein, eating more fiber/less starch, reducing consumption of juices by children). The low-carbohydrate advocates did some adjustments of their own increasingly advocating controlling fat and eliminating trans fat. Many of the diet guides and gurus that appeared at this time intentionally distanced themselves from Atkins and the term low carb (because of the controversies) even though their recommendations were based on largely the same principles (e.g. the Zone diet). As such it is often a matter of debate which diets are really low-carbohydrate and which are not. The 1990s and 2000s also saw the publication of an increased number of clinical studies regarding the effectiveness and safety (pro and con) of low-carbohydrate diets (see medical research).
After 2004 the popularity of this diet trend began to wane significantly although it still remains quite popular. In spite of the decline in popularity this diet trend has continued to quietly garner attention in the medical and nutritional science communities.
Practices and theories
The term low-carbohydrate diet today is most strongly associated with the Atkins Diet. However, there is an array of other diets that share to varying degrees the same principles (e.g. the Zone Diet, the Protein Power Lifeplan , the Go Lower Diet and the South Beach Diet). Therefore, there is no widely accepted definition of what precisely constitutes a low-carbohydrate diet. It is important to note that the level of carbohydrate consumption defined as low-carbohydrate by medical researchers may be different than the level of carbohydrate defined by diet advisors. For the purposes of this discussion, we focus on diets that reduce (nutritive) carbohydrate intake sufficiently to dramatically reduce or eliminate insulin production in the body and to encourage ketosis (production of ketones to be used as energy in place of glucose).
Although originally low-carbohydrate diets were created based on anecdotal evidence of their effectiveness, today there is a much greater theoretical basis on which these diets rest. The key scientific principle which forms the basis for these diets is the relationship between consumption of carbohydrates and the subsequent effect on blood sugar (i.e. blood glucose) and on production of some hormones. Blood sugar levels in the human body must be maintained in a fairly narrow range to maintain health. The two primary hormones related to regulating blood sugar levels, produced in the pancreas, are insulin, which lowers blood sugar levels (among many other effects, most of considerable significance metabolically), and glucagon, which raises blood sugar levels. In general, most western diets (and many others) are sufficiently high in nutritive carbohydrates that nearly all meals evoke insulin secretion from the beta cells in the pancreas; carbohydrates which are digested to produce glucose in the blood stream are the primary control for insulin secretion. Another aspect of insulin secretion is control of ketosis; in the non-ketotic state, the human body stores dietary fat in fat cells (ie, adipose tissue) and preferentially uses glucose as cellular fuel. By contrast, low-carbohydrate diets, or more properly, diets that are very low in nutritive carbohydrates, evoke less insulin (to cover the ingested glucose in the blood stream), leading to longer and more frequent episodes of ketosis. Some researchers suggest that this causes body fat to be eliminated from the body although this theory remains, at best, controversial, if it referes to excretion of lipids (ie, fat and oil) and not to fat metabolism during ketosis.
Low-carbohydrate diet advocates in general recommend reducing nutritive carbohydrates (commonly referred to as "net carbs," i.e. grams of total carbohydrates reduced by the non-nutritive carbohydrates) to very low levels. This means sharply reducing consumption of desserts, breads, pastas, potatoes, rice, and other sweet or starchy foods. Some recommend levels as low as 20-30 grams of "net carbs" per day, at least in the early stages of dieting (for comparison, a single slice of white bread typically contains 15 grams of carbohydrate, almost entirely starch). By contrast, the U.S. Institute of Medicine recommends a minimum intake of 130 grams of carbohydrate per day (the FAO and WHO similarly recommend that the majority of dietary energy come from carbohydrates).
Low-carbohydrate diets often differ in the specific amount of carbohydrates allowed, whether certain types of foods are preferred, whether occasional exceptions are allowed, etc. Generally they all agree that processed sugar should be eliminated, or at the very least greatly reduced, and similarly generally discourage heavily processed grains (white bread, etc.). They vary greatly in their recommendations as to the amount of fat allowed in the diet although the most popular versions today (including Atkins) generally recommend at most a moderate fat intake.
Although low-carbohydrate diets are
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