Low-carbohydrate diets or low-carb diets or keto or ketogenic diets are dietary programs that restrict carbohydrate consumption. 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.
Definition and classification
Low-carbohydrate diets are not well-defined.
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. A 2016 review of low-carbohydrate diets classified diets with 50g of carbohydrate per day (less than 10% of total calories) as "very low" and diets with 40% of calories from carbohydrates as "mild" low-carbohydrate diets. In a 2015 review Richard D. Feinman and colleagues proposed that a very low carbohydrate diet had less that 10% caloric intake from carbohydrate, a low carobhydate diet less that 26%, a medium carbodydrate diet less than 45%, and a high carbohydrate diet more than 45%.
The U.S. Institute of Medicine recommends a minimum intake of 130 g of carbohydrate per day.nThe FAO and WHO similarly recommend that the majority of dietary energy come from carbohydrates.
A popular misconception driving adoption of the diet for weight loss, is that by reducing carbohydrate intake dieters can in some way avoid weight gain from the calories in other macronutrients. However any weight loss resulting from a low-carbohydrate diet probably comes merely from reduced overall calorie intake.
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. 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).
Low-carbohydrate diets may improve cardiovascular risk factors and are effective for achieving weight loss. Low-carbohydrate diets are not an option recommended in the current Dietary Guidelines for Americans, which instead recommends a low fat diet. A systematic review of 62,421 participants in 10 dietary trials found that reducing dietary fat intake had no effect on coronary heart disease and had no effect on overall mortality. The authors of this meta-analysis conclude that the available evidence from randomized controlled trials does not support the recommendation of the 2015 - 2020 Dietary Guidelines for Americans that people reduce their fat intake.
As with other diet plans, people who restrict calories with a low-carbohydrate diet might lose weight. In the case of low-carbohydrate diets, weight loss is helped by the increased feeling of fullness and a tendency towards selecting nutrient-rich food. A very low-carbohydrate diet performs slightly better than a low-fat diet for long-term weight loss. The long-term effects of a low-carbohydrate diet are not known.
In persons with diabetes mellitus Type 2, a low-carbohydrate diet gives slightly better control of glucose metabolism than a low-fat diet. Limiting carbohydrate consumption is a traditional treatment for diabetes – indeed, it was the only effective treatment before the development of insulin therapy – and when carefully adhered to, it generally results in improved glucose control, usually without long-term weight loss. Some experts recommend a low-carbohydrate diet as the first, default treatment for people with diabetes.
Some studies of low carbohydrate diet permit up to 40% of dietary calories as carbohydrate, which leads to null bias, as this level of mild carbohydrate restriction is inadequate to produce the metabolic changes seen with more significant restriction of carbohydrate intake. Compared with those on a low fat diet, persons who restrict dietary carbohydrate intake to less than 26% of total dietary calorie intake have a greater reduction in body weight but a greater increase in HDL-cholesterol and also a greater increase in LDL-cholesterol.
Potential favorable changes in triglyceride and high-density lipoprotein cholesterol values should be weighed against potential unfavorable changes in low-density lipoprotein cholesterol and total cholesterol values when low-carbohydrate diets to induce weight loss are considered. A 2008 systematic review of randomized controlled studies that compared low-carbohydrate diets to low-fat/low-calorie diets found the measurements of weight, HDL cholesterol, triglyceride levels, and systolic blood pressure were significantly better in groups that followed low-carbohydrate diets. The authors of this review also found a higher rate of attrition in groups with low-fat diets, and concluded, "evidence from this systematic review demonstrates that low-carbohydrate/high-protein diets are more effective at six months and are as effective, if not more, as low-fat diets in reducing weight and cardiovascular disease risk up to one year", but they also called for more long-term studies.
There is moderately strong evidence that low carbohydrate diets are safe for most persons. However, the state of ketosis induced by the diet can occasionally progress to ketoacidosis in healthy persons. Ketoacidosis, which usually occurs only in diabetes, alcoholism or starvation, is a severe condition that requires immediate medical intervention.
As of 2014 it appeared that with respect to the risk of death for people with cardiovascular disease, the kind of carbohydrates consumed are important; diets relatively higher in fiber and whole grains lead to reduced risk of death from cardiovascular disease. Highly refined-grain diets do not.
Position of major governmental and medical organizations
American Dietetic Association
As of 2003 in commenting on a study in the Journal of the American Medical Association, a spokesperson for the American Dietetic Association reiterated the association's position that "there is no magic bullet to safe and healthful weight loss." The Association specifically endorses the high-carbohydrate diet recommended by the National Academy of Sciences. As part of the National Nutrition Month "Fact vs. Fiction" campaign in 2008, the ADA stated: "Calories cause weight gain. Excess calories from carbohydrates are not any more fattening than calories from other sources."
American Heart Association
As of 2015 the AHA stated categorically that it doesn't recommend high-protein diets. It states: "The American Heart Association doesn't recommend high-protein diets for weight loss. Some of these diets restrict healthful foods that provide essential nutrients and don't provide the variety of foods needed to adequately meet nutritional needs. People who stay on these diets very long may not get enough vitamins and minerals and face other potential health risks." A science advisory from the association further states the association's position that these diets may be associated with increased risk for coronary heart disease. Robert H. Eckel, past president, noted that a low-carbohydrate diet could potentially meet AHA guidelines if it conformed to the AHA guidelines for low fat content.
Australian Heart Foundation
The position statement by the Heart Foundation regarding low-carbohydrate diets states: "the Heart Foundation does not support the adoption of VLCARB diets for weight loss."
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 and the results are still debated in the medical community. Supporters and opponents of low-carbohydrate diets frequently cite many articles (sometimes the same articles) as supporting their positions. One of the fundamental criticisms of those who advocate the low-carbohydrate diets has been the lack of long-term studies evaluating their health risks. This has begun to change as longer term studies are emerging.
A 2012 systematic review studying the effects of a low-carbohydrate diet on weight loss and cardiovascular risk factors showed that the diet that was studied was associated with significant decreases in body weight, body mass index, abdominal circumference, blood pressure, triglycerides, fasting blood sugar, blood insulin and plasma C-reactive protein, as well as an increase in high-density lipoprotein cholesterol (HDL). Low-density lipoprotein cholesterol (LDL) and creatinine did not change significantly. The study found the LCD was shown to have favorable effects on body weight and major cardiovascular risk factors (but concluded the effects on long-term health are unknown). The study did not compare health benefits of LCD to low-fat diets.
A meta-analysis published in the American Journal of Clinical Nutrition in 2013 compared low-carbohydrate, Mediterranean, vegan, vegetarian, low-glycemic index, high-fiber, and high-protein diets with control diets. The researchers concluded that low-carbohydrate, Mediterranean, low-glycemic index, and high-protein diets are effective in improving markers of risk for cardiovascular disease and diabetes.
Criticism and controversies
Advocates of low-carbohydrate diets generally dispute any suggestion that such diets cause weakness or exhaustion (except in the first few weeks as the body adjusts), and indeed most highly recommend exercise as part of a healthy lifestyle.
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
Some critics imply or explicitly argue that vegetables and fruits are inherently all heavily concentrated sources of carbohydrates (so much so that some sources treat the words 'vegetable' and 'carbohydrate' as synonymous). While some fruits may contain relatively high concentrations of sugar, most are largely water and not particularly calorie-dense. Thus, in absolute terms, even sweet fruits and berries do not represent a significant source of carbohydrates in their natural form, and also typically contain a good deal of fiber which attenuates the absorption of sugar in the gut. Lastly, most of the sugar in fruit is fructose, which has a reported negligible effect on insulin levels in obese subjects.
Most vegetables are low- or moderate-carbohydrate foods (in the context of these diets, fiber is excluded because it is not a nutritive carbohydrate). Some vegetables, such as potatoes, have high concentrations of starch, as do maize 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 casesGlucose availability
Some evidence indicates the increasingly large percentage of calories consumed as refined carbohydrates is positively correlated with the increased incidence of metabolic disorders such as type 2 diabetes.
Some evidence indicates the human brain – the largest consumer of glucose in the body – can operate more efficiently on ketone bodies.
In 2004, the Canadian government ruled that foods sold in Canada could not be marketed with reduced or eliminated carbohydrate content as a selling point, because reduced carbohydrate content was not determined to be a health benefit. The government ruled that existing "low carb" and "no carb" packaging would have to be phased out by 2006.
Early dietary science
In 1797, John Rollo reported on the results of treating two diabetic Army officers with a low-carbohydrate diet and medications. A very low-carbohydrate, ketogenic diet was the standard treatment for diabetes throughout the nineteenth century.
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 the early 1900s Frederick Madison Allen developed a highly restrictive short term regime which was described by Walter R. Steiner at the 1916 annual convention of the Connecticut State Medical Society as The Starvation Treatment of Diabetes Mellitus. People showing very high urine glucose levels were confined to bed and restricted to an unlimited supply of water, coffee, tea, and clear meat broth until their urine was "sugar free"; this took two to four days but sometimes up to eight. After the person's urine was sugar-free food was re-introduced; first only vegetables with less than 5g of carbohydate per day, eventually adding fruits and grains to build up to 3g of carbohydrate per kilogram of body weight. Then eggs and meat were added, building up to 1g of protein/kg of body weight per day, then fat was added to the point where the person stopped losing weight or a maximum of 40 calories of fat per kilogram per day was reached. The process was halted if sugar appeared in the person's urine. This diet was often administered in a hospital in order to better ensure compliance and safety.
Modern low-carbohydrate diets
In 1958, Richard Mackarness M.D. published Eat Fat and Grow Slim, a low-carbohydrate diet with much of the same advice and based on the same theories as those promulgated by Robert Atkins more than a decade later. Mackarness also challenged the "calorie theory" and referenced primitive diets such as the Inuit as examples of healthy diets with a low-carbohydrate and high-fat composition.
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.
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.
1990s – present
In the 1990s, Atkins published an update from his 1972 book, 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 what the mass media call the "low carb craze" in the United States. During the late 1990s and early 2000s, low-carbohydrate diets became some of the most popular diets in the US. By some accounts, up to 18% of the population was using one type of low-carbohydrate diet or another at the peak of their popularity. Food manufacturers and restaurant chains like Krispy Kreme noted the trend, as it affected their businesses. Parts of the mainstream medical community have denounced low-carbohydrate diets as being dangerous to health, such as the AHA in 2001 and the American Kidney Fund in 2002. Low-carbohydrate advocates did some adjustments of their own, increasingly advocating controlling fat and eliminating trans fat.
In the United States, the diet has continued to garner attention in the medical and nutritional science communities, and also has inspired a number of hybrid diets that include traditional calorie-counting and exercise regimens.
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