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LOW-CARBOHYDRATE DIET – BANTING DIET
Low-carbohydrate diets or low-carb diets are dietary programs that restrict carbohydrate consumption, often for the treatment of obesity or diabetes. Foods high in easily digestible carbohydrates (e.g., sugar, bread, pasta) are limited or replaced with foods containing a higher percentage of fats and moderate protein (e.g., meat, poultry, fish, shellfish, eggs, cheese, nuts, and seeds) and other foods low in carbohydrates (e.g., most salad vegetables such as spinach, kale, chard and collards), although other vegetables and fruits (especially berries) are often allowed. The amount of carbohydrate allowed varies with different low-carbohydrate diets.
Such diets are sometimes 'ketogenic' (i.e., they restrict carbohydrate intake sufficiently to cause ketosis). The induction phase of the Atkins diet is ketogenic.
The term "low-carbohydrate diet" is generally applied to diets that restrict carbohydrates to less than 20% of caloric intake, but can also refer to diets that simply restrict or limit carbohydrates to less than recommended proportions (generally less than 45% of total energy coming from carbohydrates).
Low-carbohydrate diets are used to treat or prevent some chronic diseases and conditions, including cardiovascular disease, metabolic syndrome, high blood pressure, and diabetes.
A more detailed picture of early human diets before the origin of agriculture may be obtained by analogy to contemporary hunter-gatherers. According to one survey of these societies, a relatively low carbohydrate (22–40% of total energy), animal food-centred diet is preferred "whenever and wherever it [is] ecologically possible", and where plant foods do predominate, carbohydrate consumption remains low because wild plants are much lower in carbohydrate and higher in fibre than modern domesticated crops. Primatologist Katherine Milton, however, has argued that the survey data on which this conclusion is based inflate the animal content of typical hunter-gatherer diets; much of it was based on early ethnography, which may have overlooked the role of women in gathering plant foods. She has also highlighted the diversity of both ancestral and contemporary foraging diets, arguing no evidence indicates humans are especially adapted to a single Palaeolithic diet over and above the vegetarian diets characteristic of the last 30 million years of primate evolution.
The origin of agriculture brought about a rise in carbohydrate levels in human diets. The industrial age has seen a particularly steep rise in refined carbohydrate levels in Western societies, as well as urban societies in Asian countries, such as India, China, and Japan.
Early dietary science
In 1863, William Banting, a formerly 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 1888, James Salisbury introduced the Salisbury steak as part of his high-meat diet, which limited vegetables, fruit, starches, and fats to one-third of the diet.
Modern low-carbohydrate diets
In 1967, 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 United States. Other low-carbohydrate diets in the 1960s included the Air Force diet and the drinking man’s diet. Austrian physician Wolfgang Lutz published his book Leben Ohne Brot (Life Without Bread) in 1967. However, it was not well known in the English-speaking world.
In 1972, Robert Atkins published Dr. Atkins Diet Revolution, which advocated the low-carbohydrate diet he had successfully used in treating patients in the 1960s (having developed the diet from a 1963 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 Atkins had done little real research into his theories and based them mostly on his clinical work. Later that decade, Walter Voegtlin and Herman Tarnower published books advocating the Palaeolithic diet and Scarsdale diet, respectively, each meeting with moderate success.
The concept of the glycemic index was developed in 1981 by David Jenkins to account for variances in speed of digestion of different types of carbohydrates. This concept classifies foods according to the rapidity of 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 slower one. The concept has been extended to include the amount of carbohydrate actually absorbed, as well, as a tablespoonful of cooked carrots is less significant overall than a large baked potato (effectively pure starch, which is efficiently absorbed as glucose), despite differences in glycemic indices.
1990s – present
Proponents who appeared with new diet guides at that time like the Zone diet intentionally distanced themselves from Atkins and the term 'low carb' because of the controversies, though their recommendations were based on largely the same principles. It can be controversial which diets are low-carbohydrate and which are not. The 1990s and 2000s saw the publication of an increased number of clinical studies regarding the effectiveness and safety (pro and con) of low-carbohydrate diets (see low-carbohydrate diet medical research).
In the United States, the diet has continued to garner attention in the medical and nutritional science communities, and also inspired a number of hybrid diets that include traditional calorie-counting and exercise regimens. Other low-carb diets, such as the Paleo Diet, focus on the removal of certain foods from the diet, such as sugar and grain. On September 2, 2014 a small randomized trial by the NIH of 148 men and women comparing a low-carbohydrate diet with a low fat diet without calorie restrictions over one year showed that participants in the low-carbohydrate diet had greater weight loss than those on the low-fat diet. The low-fat group lost weight, but appeared to lose more muscle than fat.
The American Academy of Family Physicians defines low-carbohydrate diets as diets that restrict carbohydrate intake to 20 to 60 grams per day, typically less than 20% of caloric intake. Some low-carbohydrate diets may exceed one or more of these definitions, notably the maintenance phase of the Atkins diet. Some evidence suggests blood sugar levels in the human body should be maintained in a fairly narrow range to maintain good health.
The body of research underpinning low-carbohydrate diets has grown significantly in the decades of the 1990s and 2000s. Most research centres on the relationship between carbohydrate intake and blood sugar levels (i.e., blood glucose), as well as the two primary hormones produced in the pancreas, that regulate the blood sugar level, insulin, which lowers it, and glucagon, which raises it.
In Western diets, most meals are sufficiently high in carbohydrates to stimulate insulin secretion. The primary control for this insulin secretion is glucose in the bloodstream from digested carbohydrate. Insulin also controls ketosis; in the nonketotic state, the human body stores dietary fat in fat cells (i.e., adipose tissue) and preferentially uses glucose as cellular fuel. Diets low in carbohydrates introduce less glucose into the bloodstream and thus stimulate less insulin secretion, which leads to longer and more frequent episodes of ketosis. Some research suggests this causes body fat to be eliminated from the body. This theory is controversial, insofar as it refers to excretion of lipids (i.e., fat and oil) and not to fat metabolism during ketosis.
Although low-carbohydrate diets are most commonly discussed as a weight-loss approach, some experts have proposed using low-carbohydrate diets to mitigate or prevent diseases, including diabetes, metabolic disease, and epilepsy. Some low-carbohydrate proponents and others argue that the rise in carbohydrate consumption, especially refined carbohydrates, caused the epidemic levels of many diseases in modern society, including metabolic disease and type 2 diabetes.
A category of diets is known as low-glycemic-index diets (low-GI diets) or low-glycemic-load diets (low-GL diets), in particular the Low GI Diet. In reality, low-carbohydrate diets can also be low-GL diets (and vice versa) depending on the carbohydrates in a particular diet. 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 their effect is predictable. Low-GI/low-GL diets are based on the measured change in blood glucose levels in various carbohydrates – these vary markedly in laboratory studies. The differences are due to poorly understood digestive differences between foods. However, as foods influence digestion in complex ways (e.g., both protein and fat delay absorption of glucose from carbohydrates eaten at the same time) it is difficult to even approximate the glycemic effect (e.g., over time or even in total in some cases) of a particular meal.
The low-insulin-index diet, is similar, except 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 such diet recommendations mostly involve lowering nutritive carbohydrates, some low-carbohydrate foods are discouraged, as well (e.g., beef). Insulin secretion is stimulated (though less strongly) by other dietary intake. Like glycemic-index diets, predicting the insulin secretion from any particular meal is difficult, due to assorted digestive interactions and so differing effects on insulin release.
KETOSIS AND INSULIN SYNTHESIS: WHAT IS NORMAL?
At the heart of the debate about most low-carbohydrate diets are fundamental questions about what is a 'normal' diet and how the human body is supposed to operate. These questions can be outlined as follows.
The diets of most people in modern Western nations, especially the United States, contain large amounts of starches, including refined flours, and substantial amounts of sugars, including fructose. Most Westerners seldom exhaust stored glycogen supplies and rarely go into ketosis. This has been regarded by the majority of the medical community in the last century as normal for humans. Ketosis should not be confused with ketoacidosis, a dangerous and extreme ketotic condition associated with diabetes. Some in the medical community have regarded ketosis as harmful and potentially life-threatening, believing it unnecessarily stresses the liver and causes destruction of muscle tissues. A perception developed that getting energy chiefly from dietary protein rather than carbohydrates causes liver damage and that getting energy chiefly from dietary fats rather than carbohydrates causes heart disease and other health problems. This view is still held by the majority of those in the medical and nutritional science communities. However, it is now widely recognized that periodic ketosis is, in fact, normal, and that ketosis provides a number of surprising benefits, including neuroprotection against diverse types of cellular injury.
People critical of low-carbohydrate diets cite hypoglycemia and ketoacidosis as risk factors. While mild acidosis may be a side effect when beginning a ketogenic diet, no known health emergencies have been recorded. It should not be conflated with diabetic ketoacidosis, which can be life-threatening.
A diet very low in starches and sugars induces several adaptive responses. Low blood glucose causes the pancreas to produce glucagon, which stimulates the liver to convert stored glycogen into glucose and release it into the blood. When liver glycogen stores are exhausted, the body starts using fatty acids instead of glucose. The brain cannot use fatty acids for energy, and instead uses ketones produced from fatty acids by the liver. By using fatty acids and ketones as energy sources, supplemented by conversion of proteins to glucose (gluconeogenesis), the body can maintain normal levels of blood glucose without dietary carbohydrates.
Most advocates of low-carbohydrate diets, such as the Atkins diet, argue that the human body is adapted to function primarily in ketosis. They argue that high insulin levels can 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 mostly diabetic condition unrelated to dieting or low-carbohydrate intake). 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 beneficial. Most low-carb diet plans discourage consumption of trans fat.
On a high-carbohydrate diet, glucose is used by cells in the body for the energy needed for their basic functions, and about two-thirds of body cells require insulin to use glucose. Excessive amounts of blood glucose are thought to be a primary cause of the complications of diabetes, when glucose reacts with body proteins (resulting in glycosolated proteins) and change their behaviour. Perhaps for this reason, the amount of glucose tightly maintained in the blood is quite low. Unless a meal is very low in starches and sugars, blood glucose will rise for a period of an hour or two after a meal. When this occurs, beta cells in the pancreas release insulin to cause uptake of glucose into cells. In liver and muscle cells, more glucose is taken in than is needed and stored as glycogen (once called 'animal starch'). Diets with a high starch/sugar content, therefore, cause release of more insulin, and so more cell absorption. In diabetics, glucose levels vary in time with meals and vary a little more as a result of high-carbohydrate meals. In nondiabetics, blood-sugar levels are restored to normal levels within an hour or two, regardless of the content of a meal.
However, the ability of the body to store glycogen is finite. Once liver and muscular stores are full to the maximum, adipose tissue (subcutaneous and visceral fat stores) becomes the site of sugar storage in the form of fat. Given the body's ability to store fat is almost limitless, hence the modern dilemma of morbid obesity occurs.
While diet devoid of essential fatty acids (EFAs) and essential amino acids (EAAs) will result in eventual death, a diet completely without carbohydrates can be maintained indefinitely because triglycerides (which make up fat stored in the body and dietary fat) include a (glycerol) molecule which the body can easily convert to glucose. It should be noted that the EFAs and all amino acids are structural building blocks, not inherent fuel for energy. However, a very-low-carbohydrate diet (less than 20 g per day) may negatively affect certain biomarkers and produce detrimental effects in certain types of individuals (for instance, those with kidney problems). The opposite is also true; for instance, clinical experience suggests very-low-carbohydrate diets for patients with metabolic syndrome.
STUDIES ON HEALTH EFFECTS
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 some research has been done throughout the 20th century, most directly relevant scientific studies have occurred in the 1990s and early 2000s. 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. A significant criticism of the diet trend was that no studies evaluated the effects of the diets beyond a few months. However, studies emerged which evaluate these diets over much longer periods, controlled studies as long as two years and survey studies as long as two decades.
A systematic review published in 2014 included 19 trials with a total of 3,209 overweight and obese participants, some with diabetes. The review included both extreme low carbohydrate diets high in both protein and fat, as well as less extreme low carbohydrate diets that are high in protein but with recommended intakes of fat. The authors found that when the amount of energy (kilojoules/calories) consumed by people following the low carbohydrate and balanced diets (45 to 65% of total energy from carbohydrates, 25 to 35% from fat, and 10 to 20% from protein) was similar, there was no difference in weight loss after 3 to 6 months and after 1 to 2 years in those with and without diabetes. For blood pressure, cholesterol levels and diabetes markers there was also no difference detected between the low carbohydrate and the balanced diets. The follow-up of these trials was no longer than two years, which is too short to provide an adequate picture of the long term risk of following a low carbohydrate diet.
In one theory, one of the reasons people lose weight on low-carbohydrate diets is related to the phenomenon of spontaneous reduction in food intake.
Carbohydrate restriction may help prevent obesity and type 2 diabetes, as well as atherosclerosis.
OPINIONS FROM MAJOR GOVERNMENTAL AND MEDICAL ORGANIZATIONS
Opinions regarding low-carbohydrate diets vary throughout the medical and nutritional science communities, yet government bodies, and medical and nutritional associations, have generally opposed this nutritional regimen. Since 2003, some organizations have gradually begun to relax their opposition to the point of cautious support for low-carbohydrate diets. Some of these organizations receive funding from the food industry. Official statements from some organizations:
American Academy of Family Physicians
American Diabetes Association
American Dietetic Association
American Heart Association
Australian Heart Foundation
National Health Service (UK)
Heart & Stroke Foundation (Canada)
National Board of Health and Welfare (Sweden)
In recommendation for diets suitable for diabetes patients published in 2011 a moderate low-carb option (30–40%) is suggested.
U.S. Department of Health and Human Services
CRITICISM AND CONTROVERSIES
Water-related weight loss
Arctic cultures, such as the Inuit, were found to lead physically demanding lives consuming a diet of about 15–20% of their calories from carbohydrates, largely in the form of glycogen from the raw meat they consumed. However, studies also indicate that while low-carb diets will not reduce endurance performance after adapting, they will probably deteriorate anaerobic performance such as strength-training or sprint-running because these processes rely on glycogen for fuel.
Vegetables and fruits
Most vegetables are low- or moderate-carbohydrate foods (in the context of these diets, fibre is excluded because it is not a nutritive carbohydrate). Some vegetables, such as potatoes and carrots, have high concentrations of starch, as do corn and rice. Most low-carbohydrate diet plans accommodate vegetables such as broccoli, spinach, cauliflower, and peppers. The Atkins diet recommends that most dietary carbs come from vegetables. Nevertheless, debate remains as to whether restricting even just high-carbohydrate fruits, vegetables, and grains is truly healthy.
Contrary to the recommendations of most low-carbohydrate diet guides, some individuals may choose to avoid vegetables altogether to minimize carbohydrate intake. Low-carbohydrate vegetarianism is also practiced.
Raw fruits and vegetables are packed with an array of other protective chemicals, such as vitamins, flavonoids, and sugar alcohols. Some of those molecules help safeguard against the over-absorption of sugars in the human digestive system. Industrial food raffination depletes some of those beneficial molecules to various degrees, including almost total removal in many cases.
Micronutrients and vitamins
In addition, this claim neglects the nature of the carbohydrates ingested. Some are indigestible in humans (e.g., cellulose), some are poorly digested in humans (e.g., the amylose starch variant), and some require considerable processing to be converted to absorbable forms. In general, uncooked or unprocessed (e.g., milling, crushing, etc.) foods are harder (typically much harder) to absorb, so do not raise glucose levels as much as might be expected from the proportion of carbohydrate present. Cooking (especially moist cooking above the temperature necessary to expand starch granules) and mechanical processing both considerably raise the amount of absorbable carbohydrate and reduce the digestive effort required.
Analyses which neglect these factors are misleading and will not result in a working diet, or at least one which works as intended. In fact, some evidence indicates the human brain – the largest consumer of glucose in the body – can operate more efficiently on ketones.
Some variants of low-carbohydrate diets involve substantially lowered intake of dietary fibre, which can result in constipation if not supplemented. For example, this has been a criticism of the induction phase of the Atkins diet (the Atkins diet is now clearer about recommending a fibre supplement during induction). Most advocates today argue that fibre is a "good" carbohydrate and encourage a high-fibre diet.
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