Low-carbohydrate diets or low carb diets, are food Dieting for weight loss and dietary health that advocate restricted carbohydrate consumption, based on research that ties carbohydrate consumption with increased blood insulin levels, and increased insulin with obesity.
Under these various dietary programs, foods containing carbohydrates (like sugar, grains, and starches) are limited or replaced in favor of foods containing more protein and fat. Vegetables, though classified as carbohydrates, are thought to be far healthier than grain-based carbohydrates. Programs such as the South Beach diet, Atkins Nutritional Approach and Zone diet diets, are claimed to "work" because they reduce insulin levels, which in turn causes the body to burn its fat for energy.
As a process, these kinds of diets have been in and out of fashion since the William Banting appeared in the 19th century. But long before modern scientific invention, anecdotal and holistic medicine prescriptions, containing passages about limiting certain foods, including foods of mostly carbohydrates, have appeared throughout history. Although strong evidence suggests, and general agreement claims, that low carb diets can help achieve weight loss, some have been controversial among nutritionists, and their relative safety has been challenged.
Low-carb diets are largely distinguished by the proportions of carb intake they recommend, and the method or methods used to determinine which source or sources of carbohydrates should be consumed and which should be avoided. While all agree that processed sugar should be eliminated, or at the very least greatly reduced, they often differ on the recommended levels of grains, fruits and vegetables, though there is broad agreement that, in general, vegetables are better than fruits, and fruits are better than grains.
Some advocates of low carb diets believe that humans did not evolve to eat the typical modern Western diet, reliant on processed grains, starches, and refined sugar, and that their consumption causes undesired and largely unknown effects. Specifically, it is argued that they cause the body to produce excess amounts of the hormone insulin, which tells the body to store rather than burn fat, hence causing obesity and its complications (heart disease, cancer, diabetes). They claim that humans evolved to eat a diet which consisted mainly of meat and that the current "epidemic" of obesity is due to the popular assumption, reinforced by the food industry and the new field of dietary medicine, that the low-fat approach is healthier.
Supporters claim the exclusive focus on reducing fat is oversimplified, and that low-fat diets are not automatically healthy ones. The western world is not suffering from a collective failure of will to exercise, but has been encouraged to eat more carbohydrates, which in turn stimulate appetite and more eating.
The recent rise in western obesity rates has coincided with a widespread belief in low-fat, high-carbohydrate as a healthy way of eating. By contrast traditional, high-fat French cooking has a lead to a much lower incidence of obesity, morbid obesity and chronic heart disease than in the high-sugar American diet, despite overall energy intake and exercise levels being the same.
Advocates point to scientific trials demonstrating the efficacy and safety of the diet. Several independent clinical trials have shown that low carb diets can successfully be used to lose weight. The trials were all of short duration and were not able to assess the long-term health effects of the diet, but the trials did find that, at least in the short term, risk factors for heart disease and diabetes, such as blood serum cholesterol and insulin levels, tended to improve, despite the increased consumption of saturated fat and cholesterol.
One study, conducted in 1965 at the Oakland Naval Hospital, showed that a diet of 1000 calories per day, high in fat and with carbohydrates limited to 10 grams (40 calories) of total intake, resulted in greater body fat loss over a 10-day period than complete fasting (#External sources). Some advocates of low-carbohydrate diets have termed this the metabolic advantage of such diets.
Critics contend that low carbohydrate diets are not without harmful side effects. Very low carbohydrate consumption can lead to the metabolic state called ketosis, which may cause headaches, tiredness, nausea, dehydration, dizziness, and an unusual sweet-smelling breath odor. The lowered intake of dietary fiber that often accompanies dramatically reduced carbohydrate intake (such as in the Induction stage of the Atkins Nutritional Approach) can result in constipation if not supplemented.
Replacement of calories from carboydrates with meat may result in high consumption of saturated fat and cholesterol, which many authorities believe will increase the risk of heart disease. Moreover, it has been hypothesised that the kidneys can become overworked and that a related change in blood acidity can lead to bone loss, but trials testing the hypothesis have found no evidence of kidney damage or loss of bone.
Critics of low-carbohydrate diets also point out that from an environmental point of view an increased consumption of animal protein places a great burden on the world's natural resources and is not sustainable. They also point out that the explosive growth in global population over the last few centuries was only possible because of grain crops.
Advocates of the diet counter environmental criticisms by arguing that the majority of grain farm land was formerly poor quality pasture fit only for raising livestock and that it has been turned to grain production only through massive government subsidy and the use of environmentally questionable fertilizers and pesticides.
Food producers have ascribed a commercial impact to the growing popularity of low-carbohydrate diets in recent years. For example, in May 2004, New World Pasta filed for bankruptcy protection, claiming that low-carbohydrate diets were reducing demand for pasta. In the same month, Krispy Kreme warned investors that its earnings would be below projections, and blamed low-carbohydrate diets on reduced demand for its products.
Other producers have taken advantage of the trend. In response to consumer demand for low-carb foods, the food industry has been marketing low-carb products in recent years and restaurants are increasingly offering low carb menus. These items typically replace carbohydrate-laden wheat flour with high-protein soy flour and replace sugar with artificial sweeteners such as sucralose and sugar alcohols.
