Ebook The Impact of Low-carbohydrate Diets on Glycemic Control and Weight Management in Patients With Type 2 Diabetes
Low-carbohydrate diets that provide <45% of energy from carbohydrates have been a popular method for individuals with type 2 diabetes mellitus to achieve weight loss (1).Type 2 diabetes is a major health challenge in Canada, affecting >4.1 % of adults or 1 063 698 persons in 2001 (2).However,its true prevalence is estimated to be >7% (2.2 million people) based on population studies that indicate it to be >30% higher than that derived from physicians’ diagnoses(3). Furthermore, 80 to 90% of these patients are overweight or obese (3).The prevalence of obesity is also a health concern affecting 23% of Canadian adults (2). Obesity is an independent risk factor for type 2 diabetes and the reason weight loss through change in lifestyle is highly recommended in both prevention and treatment of the disease (3,4).However, the challenges of losing and maintaining weight loss are well documented for obese idividuals with diabetes (5). Because therapeutic attempts are often unsuccessful (6),the appeal of popular diet strategies for rapid weight loss has increased. In the United States (US), >20% of dieters report having used fad and popular diets (7).
Diets that recommend reducing dietary carbohydrates (e.g.Atkins diet, South Beach diet and Zone diet) have gained widespread popularity (6) and have cut into the profits of potato farmers, bakeries and pasta-makers. According to Statistics Canada, the yield of potatoes has been voluntarily reduced for the first time since 1988 (8).This craze, however, may not be a trend, but rather a fad, as indicated by the company Atkins Nutritionals Inc. filing for bankruptcy court protection in 2005. Nevertheless, the food industry has responded by marketing >930 low-carbohydrate food products in the last 5 years (9), making the low-carbohydrate diet less boring, but possibly less effective if some of the weight loss induced by these diets is due to their monotony and lower caloric content (10,11). According to the National Purchase Diary (NPD) Group survey, 75% of people reporting that they were following a low-carbohydrate diet ate a mean of 128 g of carbohydrate per day — 6 times what most very low-carbohydrate diets would recommend. Furthermore, according to this survey, many did not know which foods contained carbohydrates (12).
The popularity of low-carbohydrate diets has generated concern within the healthcare profession about their efficacy,tolerance, adverse effects and safety (13-16); the media has asked for the “return of the carbs,” while personal testimonials from members of the public have questioned why some people are successful in losing weight when adopting such diets (16). Proponents of low-carbohydrate diets believe that hyperinsulinemia and insulin resistance contribute to the development of obesity (6,15,16) and assume that by limiting carbohydrates insulin levels will be lowered and fat storage decreased, thereby enabling fat to be mobilized for energy. In Atkins Diabetes Revolution, carbohydrates are restricted to <20 g/day until glycemic control is attained. Carbohydrates are reintroduced only if glycemic control (based on a glycemic ranking that combines glycemic index,glycemic load and net carbohydrate) is maintained.
Carbohydrate content in these diets may vary from very low (<20 g/day in the induction phase of the Atkins diet) to low (<40% of energy as in the Zone diet), both of which are inconsistent with Canada’s Guidelines for Healthy Eating, the Dietary Reference Intake for carbohydrate (³130 g/day and ³45% contribution to energy) and the Canadian Diabetes Association 2003 Clinical Practice Guidelines for the Prevention and Management of Diabetes in Canada (3). Because of this inconsistency, the National Nutrition Committee (NNC) of the Canadian Diabetes Association reviewed the scientific evidence regarding potential benefits and risks associated with the use of low-carbohydrate diets by adults with or without type 2 diabetes for weight management and with type 2 diabetes for glycemic control. This report by the NNC focuses on popular low-carbohydrate diets, for which long-term use has been studied in a controlled manner, and provides practical advice on how a health professional can evaluate the safety of such diets.
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