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Many nutrition experts disagree with the basic premise of the Atkins Diet—the notion that high-carbohydrate, low-fat diets cause obesity. For evidence of the implausibility of the Atkins Diet, some nutritionists point out that the traditional Japanese diet is very high in carbohydrates, low in protein, and very low in fat; however, before the introduction of high-fat and high-protein Western foods, being overweight was rare in Japan. Such findings make sense because ounce for ounce, carbohydrates contain far fewer calories than do fats. These critics blame eating too many calories (from any source) and lack of physical activity as the primary causes of obesity.

Critics also express concern about the impact of the Atkins Diet on the overall health of the dieter. Depending on the foods chosen by the dieter, the diet may contain a large amount of saturated fat and cholesterol, putting those at risk for heart disease in danger. Recent research has found that high-protein diets speed up the progression of hardening of the arteries (atherosclerosis), the main cause of heart attacks. Moreover, contrary to Atkins’ claims, extremely low-fat diets have been found to partially reverse heart disease. In addition, the lack of grains, fruits, and vegetables in the Atkins Diet may lead to deficiencies of key nutrients, including dietary fibre, vitamin C, folic acid, and a few minerals. Finally, high protein diets may increase the risk of osteoporosis and accelerate the rate of deterioration in kidney function associated with aging.

Critics concede that Atkins dieters often experience significant weight loss during the initial stages of the diet. However, these critics argue that the diet has a diuretic effect and that the initial weight loss is due to water loss, not fat loss. Eventually the body restores its water and sodium balance, and the rate of weight loss declines. Critics also note that there is no evidence showing that the Atkins diet leads to greater weight loss than do other diets that provide more carbohydrates, yet the same number of calories.

Studies published between 2002 and 2006 tend to support the short-term effectiveness of the Atkins diet, although not unquestionably. When compared with people who eat a low-fat diet, Atkins dieters can lose more weight in the first 6 months, but by 12 months there is no difference in the amount of total weight lost. In addition, while the Atkins diet does not appear to cause some of the adverse effects about which critics are concerned, there is evidence that the diet might cause bone loss, and other concerns about long-term safety still remain.

In a six-month study of overweight adults, many of whom had diabetes, those following the Atkins diet lost an average of 12.8 pounds, compared with only 4.2 pounds for those consuming a low-fat diet. Similar results were seen in a study of non-diabetic overweight adults, although the advantage of the Atkins diet over the low-fat diet diminished after six months. In a study of overweight adolescents, the average weight loss after 12 weeks was 21.8 pounds in the children consuming the Atkins diet, compared with 9 pounds in those consuming a low-fat diet. The greater weight loss occurred even though the Atkins group consumed 67% more calories per day than did the low-fat group.

With regard to safety factors, there were no adverse effects on cholesterol and triglyceride levels. On the contrary, in one study the Atkins diet was more effective than the low-fat diet for improving triglyceride levels. Other laboratory tests, however, suggested that long-term use of the Atkins diet could increase the risk of kidney stones and osteoporosis. Furthermore, one study found a 2.2% reduction in bone density after only six weeks on the diet. In addition, overweight people who followed the Atkins diet for 12 months were found to have a worsening of endothelial function, when compared with overweight people who consumed a high-carbohydrate, low-fat diet.¹ Impaired endothelial function is considered to be an early sign of atherosclerosis (hardening of the arteries).