The Atkins Nutritional Approach,
popularly known as the Atkins Diet or just Atkins, is the most marketed and well-known low-carbohydrate diet. It was adapted by Dr. Robert Atkins in the 1960s from a diet he read in the Journal of the American Medical Association and utilized to resolve his own overweight condition following medical school and graduate medical training. After successfully treating over ten thousand patients, he popularized the Atkins diet in a series of books, starting with Dr. Atkins' Diet Revolution in 1972. In his revised book, Dr. Atkins' New Diet Revolution, Atkins updated some of his ideas, but remained faithful to the original concepts.
The Atkins franchise, a business formed to provide products to those individuals on the diet, has been highly successful due to the popularity of the diet, and is considered the iconic and driving entity of the larger "low-carb craze". However, various factors have led to its dwindling success and the company founded by Dr. Atkins in 1989, Atkins Nutritionals of Ronkonkoma, New York, filed for Chapter 11 bankruptcy in July of 2005, two years after the death of Dr. Atkins. The company re-emerged in January 2006, and the Atkins logo is still highly visible through licensed-proprietary branding for food products and related merchandise.

Nature of the diet
The Atkins Diet represents a departure from prevailing theories. Atkins claimed there are two main unrecognized factors about Western eating habits, arguing firstly that the main cause of obesity is eating refined carbohydrates, particularly sugar, flour, and high-fructose corn syrups; and secondly, that saturated fat is overrated as a nutritional problem, and that only trans fats from sources such as hydrogenated oils need to be avoided. Consequently, Dr. Atkins rejected the advice of the food pyramid, instead asserting that the tremendous increase in refined carbohydrates is responsible for the rise in metabolic disorders of the 20th century, and that the focus on the detrimental effects of dietary fat has actually contributed to the obesity problem by increasing the proportion of insulin-inducing foods in the diet. While most of the emphasis in Atkins is on the diet, nutritional supplements and exercise are considered equally important elements.

Atkins involves the restriction of carbohydrates in order to switch the body's metabolism from burning glucose to burning stored body fat. This process (called lipolysis) begins when the body enters the state of ketosis as a consequence of running out of excess carbohydrates to burn. Dr. Atkins in his book New Diet Revolution claimed that the low-carbohydrate diet produces a "metabolic advantage" where the body burns more calories, overall, than on normal diets, and also expels some unused calories. He cited one study where he estimated this advantage to be 950 calories (4.0 MJ) a day.

Atkins restricts "net carbs", or carbohydrates that have an effect on blood sugar. Net carbohydrates can be calculated from a food source by subtracting sugar alcohols and fiber (which are shown to have a negligible effect on blood sugar levels) from total carbohydrates. Sugar alcohols need to be treated with caution, because while they may be slower to convert to glucose, they can be a significant source of glycemic load and can stall weight loss. Fructose (eg, as found in many industrial sweeteners) also contributes to caloric intake, though outside of the glucose-insulin control loop.

Preferred foods in all categories are whole, unprocessed foods with a low glycemic load. Atkins Nutritionals, the company responsible for marketing the Atkins Diet, recommends that no more than 20% of calories eaten while on the diet come from saturated fat. According to his book Atkins Diabetes Revolution, for people whose blood sugar is abnormally high or who have type-2 diabetes, this diet decreases or eliminates the need for drugs to treat these conditions. The Atkins Blood Sugar Control Program (ABSCP) is an individualized approach to weight control and permanent management of the risk factors for diabetes and cardiovascular disease.

Several randomized,

controlled studies, published in peer-reviewed journals, have concluded that dieters on the Atkins diet have achieved weight loss comparable to or greater than other diets, up to 1 year. Blood lipids have also improved, and no serious adverse effects have been observed. There are no rigorous studies to show the results after 1 year.
In the largest, most recent randomized, controlled study, published in JAMA (March 7, 2007), by Gardner at Stanford University, women "lost more weight and experienced more favorable overall metabolic effects at 12 months" than in other diets. The study followed 311 premenopausal, nondiabetic women, age 25-50. The women lost significantly more weight (mean 4.7 kg) on the Atkins diet than on 3 higher-carbohydrate diets (LEARN 2.6 kg, Ornish 2.2 kg, and Zone 1.6 kg), without increasing cardiovascular risks. Changes in HDL cholesterol, triglycerides, and mean blood pressure significantly favored Atkins over the other three diets. The authors conclude: "Concerns about adverse metabolic effects of the Atkins diet were not substantiated within the 12-month study period."

When the Atkins diet was introduced in the 1970s,

it was immediately attacked by existing experts, who claimed it was unhealthy and would fail. For example, Atkins testified before the Senate Select Committee on Nutrition and Human Needs, in April, 1973. That day, "three authorities in nutrition and health ... [testified] that Atkins's severely carbohydrate-restricted diet was neither revolutionary, effective, or safe," and a comment by Harvard nutritionist Fred Stare was read into the record: "The Atkins diet is nonsense.... Any book that recommends unlimited amounts of meat, butter and eggs, as this does, in my opinion is dangerous. The author who makes the suggestion is guilty of malpractice." Subsequent studies have not supported those fears:
"The low-carbohydrate diet produced a greater weight loss for the first six months, but the differences were not significant at one year. The low-carbohydrate diet was associated with a greater improvement in some risk factors for coronary heart disease. Adherence was poor and attrition was high in both groups. Longer and larger studies are required to determine the long-term safety and efficacy of low-carbohydrate, high-protein, high-fat diets." — New England Journal Of Medicine, Volume 348, Pages 2082-2090, 22 May 2003, Number 21
A study comparing weight loss and metabolic changes in obese adults randomly assigned to either a low-carbohydrate diet or a conventional weight loss diet at the Philadelphia Veterans Affairs Medical Center concluded the following: "Participants on a low-carbohydrate diet had more favorable overall outcomes at 1 year than did those on a conventional diet. Weight loss was similar between groups, but effects on atherogenic dyslipidemia and glycemic control were still more favorable with a low-carbohydrate diet after adjustment for differences in weight loss."
"sustained weight loss [at 6 months]" — Atkins funded, non-randomized, non-control intervention trial, American Journal of Medicine, Volume 113, Issue 1, July 2002, Pages 30-36.
A 2-week study on studying restricted carbohydrate intake in 10 obese patients with type 2 diabetes concluded: "In a small group of obese patients with type 2 diabetes, a low-carbohydrate diet followed for 2 weeks resulted in spontaneous reduction in energy intake to a level appropriate to their height; weight loss that was completely accounted for by reduced caloric intake; much improved 24-hour blood glucose profiles, insulin sensitivity, and hemoglobin A1c; and decreased plasma triglyceride and cholesterol levels. The long-term effects of this diet, however, remain uncertain." This was not a controlled study in that there was no control group; it merely observed the effect of putting ten obese diabetics on a carbohydrate restricted diet - not specifically the Atkins diet.

The strongest evidence is randomized,

controlled studies published in peer-reviewed journals. The greater the number of subjects, and the longer the subjects are followed, the more powerful the study. To date, the longest studies are 1 year, so the effects of the diet over longer durations are not known.
The medical principles and scientific theory behind the Atkins diet were first explained in a series of articles by Dr. Richard D. Feinman, a professor of biochemistry and medical researcher at State University of New York (SUNY) Health Science Center (Downstate) at Brooklyn. Feinman, president of the Nutrition & Metabolism Society, published work which attempts to prove the common idea that "a calorie is a calorie" is not correct. His research aims to demonstrate why the diet is nutritionally sound and to elucidate principles which prove Atkins scientifically correct. Proponents of the Atkins diet feel much of the criticism leveled at the diet comes from statements and opinions of individuals and associations, rather than from controlled and reviewed studies. Advocates of the diet dispute criticisms, such as the fact that a low-carbohydrate diet is likely to be high-fat and allegations that fat, especially saturated fat, is harmful. Atkins backers maintain that, unlike trans fat, which can result from partial hydrogenation, fully saturated fat is not harmful. Proponents cite the award-winning science writer Gary Taubes who, in a 2001 article in Science, 291 (5513): 2536, claimed that the oft-cited "consensus" opinion against saturated fats derives from political rather than scientific motives. Taubes' 2007 book Good Calories, Bad Calories: Challenging the Conventional Wisdom on Diet, Weight Control, and Disease also makes this point, but in more depth.
Critics of the Atkins diet may focus particularly on Atkins, or on low-carbohydrate dieting in general. Proponents claim that critics fail to consider that people are built differently, and as with any diet, the Atkins Nutritional Approach may not be effective for some people.
Continuing research supports the idea that saturated fat may be cardio-protective in some populations.
The May 22, 2003, issue of the New England Journal of Medicine published two scientific, randomized studies comparing standard low-fat diets to low-carbohydrate diets such as the Atkins Diet. In both studies, subjects lost more weight on the low-carbohydrate plans at 6-months but not at 1-year. The editors noted that "Adherence was poor and attrition was high in both groups. Longer and larger studies are required to determine the long-term safety and efficacy of low-carbohydrate, high-protein, high-fat diets."
A research study carried out by the Weight and Eating Disorders Program at the University of Pennsylvania, reported in May 2003 that the Atkins diet raised levels of HDL (or "good") cholesterol by an average of 11% and reduced the amount of triglycerides in the bloodstream by 17%. This counters one of the chief criticisms of Atkins' approach, which is that cholesterol is raised by eating fatty foods and meat.
In another study, conventional dieters' HDL cholesterol raised by 1.6% while their triglyceride levels improved. Weight loss was also statistically greater in the Atkins dieters after three and six months compared with the conventional dieters (although this did not remain statistically significant after a year). The study followed the diets of 63 obese men and women. (See New Scientist, 21 May 2003.)
The results of studies from Stanford University (2007) and Duke University (2005) favored low-carbohydrate diets for both weight loss and health indicators.