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.
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.
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.
In 1975, Walter Voegtlin published a book advocating a Stone age diet, in which he recommends sharply limiting most common sources of carbohydrates.
In 1979, Dr Herman Tarnower published the Scarsdale diet which contains only 34.5% carbohydrates and brings about the process of ketosis.
The concept of the glycemic index was invented in 1981 by Dr. David Jenkins. This concept evaluates foods according to their insulin demand -- with fast digesting simple carbohydrates having a high insulin demand and slower digesting complex carbohydrates such as grains having a lower insulin demand.
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, in fact, 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 popuarlity this diet trend has continued to quietly garner attention in the medical and nutritional science communities.
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 their effects on blood sugar (i.e. blood glucose) and hormone production. 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, and glucagon, which raises blood sugar levels. In general, most western diets (and many others) are sufficiently high in nutritive carbohydrates that virtually every meal causes substantial insulin production and avoids ketosis, thus causing excess energy in the diet to be stored as fat (discussed in the next section). By contrast, low-carbohydrate diets, or more properly, diets that are very low in nutritive carbohydrates, discourage insulin production and tend to cause ketosis. Some researchers suggest that this causes excess dietary energy and body fat to be eliminated from the body although this theory remains, at best, controversial.
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.
It has been argued by some low-carbohydrate proponents that it is the rise in carbohydrate consumption, especially refined carbohydrates, that has caused epidemic levels of many diseases in modern society.
As a related note, there is a set of diets known as low-glycemic-index diets (low-GI diets) or low-glycemic-load diets (low-GL diets), in particular the Low GI Diet by Brand-Miller et al. In reality, low-carbohydrate diets are, literally speaking, low-GL diets (and vice versa) in that they specifically limit what contributes to the glycemic load in foods. In practice, though, "low-GI"/"low-GL" diets differ from "low-carb" diets in the following ways. First, low-carbohydrate diets treat all nutritive carbohydrates as having the same effect on metabolism and generally assume that their effect is independent of other nutrients in food. Low-GI/low-GL diets base their recommendations on the actual measured metabolic (glycemic) effects of the foods eaten. Second, as a practical matter, low-GI/low-GL diets generally do not recommend diets with glycemic loads low enough to minimize insulin production and induce ketosis, whereas low-carbohydrate diets generally do.
Another related diet type, the low-insulin-index diet, is very similar except that it is based on measurements of direct insulemic responses (i.e. the amount of insulin in the bloodstream) to food rather than glycemic response (the amount of glucose in the bloodstream). Although the diet recommendations mostly involve lowering nutritive carbohydrates, there are some low-carbohydrate foods that are discouraged as well (e.g. beef).
By contrast, if the diet is very low in starches and sugars (low-carbohydrate diets) the blood sugar level can fall so low that there is insufficient glucose to fuel the cells in the body. This state causes the pancreas to produce glucagon. Glucagon causes the conversion of stored glycogen to glucose and, once the glycogen stores are exhausted, causes the liver to synthesize ketones (ketosis) and glucose (gluconeogenesis) from fats and proteins, respectively. Most cells in the body can use ketones for energy instead of glucose, and since ketones are easier to produce, only a small amount of glucose is created (in other words, ketosis is the more significant process in this case). Because diets low in starches and sugars do not tend to directly affect blood sugar levels significantly, meals tend to have little direct effect on insulin levels (and so such diets tend to discourage insulin production in general).
The diets of most people in modern western nations, especially the United States, contain significant amounts of starches (and, frequently, significant amounts of sugars). As such, the metabolisms of most westerners tend to operate outside of ketosis and tend to involve significant insulin production. This has been regarded by medical science in the last century as being normal. Ketosis has generally been regarded as a dangerous (potentially life-threatening) state which unnecessarily stresses the liver and causes destruction of muscle tissues. The view that has been developed is that getting energy more from protein than carbohydrates causes liver damage and that getting energy more from fats than carbohydrates causes heart disease and other health problems. This view is still the view of the majority in the medical and nutritional science communities.
Most advocates of low-carbohydrate diets (specifically those that recommend diets similar to the Atkins Diet) argue that maintaining a metabolic state where glucose is the primary energy source in the body is not normal at all and that the human body is, in fact, supposed to function primarily in ketosis. They argue that high insulin levels can, in fact, cause many health problems, most significantly, fat storage and weight gain. They argue that the purported dangers of ketosis are unsubstantiated (some of the arguments against ketosis result from confusion between ketosis and ketoacidosis which is a related but very different process). They also argue that fat in the diet only contributes to heart disease in the presence of high insulin levels and that if the diet is instead adjusted to induce ketosis, fat and cholesterol in the diet are not a major concern (although most do not advocate unrestricted fat intake and do advocate avoiding trans fat). Further it is argued that, whereas insulin in the bloodstream causes storage of food energy, when the body is in ketosis, excess ketones (which contain excess energy) are excreted in the urine and the breath.
Because of the substantial controversy regarding low-carbohydrate diets and even disagreements in interpreting the results of specific studies it is difficult to objectively summarize the research in a way that reflects scientific consensus. Although there has been some research done throughout the twentieth century, most directly relevant scientific studies have occurred in the 1990s and early 2000s and, as such, are relatively new. Researchers and other experts have published articles and studies that run the gamut from promoting the safety and efficacy of these diets to questioning their long-term validity to outright condemning them as dangerous. Until recently a significant criticism of the diet trend was that there were no studies that evaluated the effects of the diets beyond a few months. However, studies are emerging which evaluate these diets over much longer periods, controlled studies as long as two years and survey studies as long as two decades.
In addition to research on the efficacy of the diets some research has directly addressed other areas of health affected by low-carbohydrate diets. For example, contrary to popular belief that low-carbohydrate diets damage the heart, one study found that women eating low-carbohydrate, high-fat/protein diets had the same or slightly less risk of coronary heart disease, compared to women eating high-carbohydrate, low-fat diets. Other studies have found possible benefits to individuals with diabetes, cancer, and autism. The ketogenic diet, with 90% of energy from fat and much of the remaining from protein, has been used since the 1920s to treat epilepsy. Modern effective anticonvulsant drugs mean that it is now used only for children with difficult-to-control epilepsy. Nevertheless some studies demonstrate potentially harmful effects of low-carbohydrate diets including various metabolic and emotional side-effects.
Medical consensus on the interpretation of the research remains elusive and it is still strongly debated.
The AHA has been one of the most adamant opponents of low-carbohydrate diets. Notably, though, Dr. Robert Eckel, past president of the association, was quoted as saying that "a low-carb approach is consistent with heart association guidelines so long as there are limitations on the kinds of saturated fats often consumed by people on the Atkins diet.Australian Heart Foundation The position statement by the Heart Foundation regarding low-carbohydrate diets states that "the Heart Foundation does not support the adoption of VLCARB diets for weight loss. Although the statement clearly recommends against use of low-carbohydrate diets it makes clear that their major concern is saturated fats as opposed to carbohydrate restriction and protein. Moreover, other statements suggest that their position might be re-evaluated in the event of more evidence from longer-term studies.Food Standards Agency (UK) The consumer advice statements of the FSA regarding low-carbohydrate diets state that "rather than avoiding starchy foods, it's better to try and base your meals on them." They further state concerns regarding fat consumption in low-carbohydrate diets.Heart & Stroke Foundation (Canada) The official position statement of the Heart & Stroke Foundation states "Do not follow a low carbohydrate diet for purposes of weight loss. They state concerns regarding numerous health risks particularly those related to high consumption of "saturated and trans fats".National Board of Health and Welfare (Sweden) In 2008, the Socialstyrelsen in Sweden altered its standing regarding low-carbohydrate diets. Although formal endorsement of this regimen has not yet appeared the government has given its formal approval for using it for medically supervised weight loss.U.S. Department of Health and Human Services The HHS issues consumer guidelines for maintaining heart health which state regarding low-carbohydrate diets that "they're not the route to healthy, long-term weight management. Nevertheless HHS has issued some statements indicating wavering on this position.
It should be noted that, contrary to the recommendations of most low-carbohydrate diet guides, some individuals may choose to avoid vegetables altogether in order to minimize carbohydrates. It is more likely that such a diet could be nutritionally deficient. It should also be noted that low-carbohydrate vegetarianism can be and is practiced successfully.
Some variants of low carbohydrate diets involve substantially lowered intake of dietary fiber which can result in constipation if not supplemented. For example, this has been a criticism of the Induction stage of the Atkins diet (note that today the Atkins diet is more clear about recommending a fiber supplement during Induction). Most advocates today argue that fiber is a "good" carbohydrate and in fact encourage a high-fiber diet.
It has been hypothesized that a diet related change in blood acidity can lead to bone loss through a process called ketoacidosis, as mentioned earlier in this article. However ketoacidosis, which is often confused with ketosis, is an acute medical condition caused by extreme fasting or as a symptom of untreated diabetes, and is not likely to be induced by a proper low-carbohydrate diet.
One of the occasional side effects of a ketogenic diet is a noticeable smell of ketones in the urine, perspiration, and breath. This is caused by the temporary metabolism of fatty-acid derived acetyl-coa into the ketone form, so that it may be released from the liver into the blood stream. The ketones are then re-assembled when they reach various body tissues to form acetyl-coa again, which is used as the precursor to energy.
Has carbohydrate-restriction been forgotten as a treatment for diabetes mellitus? A perspective on the ACCORD study design.(Commentary)
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