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Am Fam Physician. 2006;73(11):1896-1901

See related article on page 1942.

Dieting is a national pastime in the United States, yet this preoccupation has done little to stem the tide of the obesity epidemic. In the past two decades, the prevalence of obesity in this country has doubled.1

The past few years have seen an interest in low-carbohydrate diets, which are a departure from the recommended low-fat dietary plans. Last and Wilson2 review low-carbohydrate diets in this issue of American Family Physician, and a position statement on the Atkins diet is available on the American Academy of Family Physicians' Web site.3

The successful promotion of low-fat diets may have had an inadvertent role in the obesity epidemic. As the percentage of total calories from fats in American diets declined, Americans compensated with an increase in total calories consumed, mainly from carbohydrates. Despite some improvement in the intake of whole grains, fruits, and vegetables, this increase in calories has come disproportionately from sugar and refined carbohydrates.4 Poor dietary choices have been compounded by larger portion sizes and less exercise. The result is that more than 60 percent of the adult population is overweight or obese, and children are at an increased risk as well.1

Obesity is a multifactorial, chronic disease. Good dietary habits, social support, and exercise are keys to successful management of obesity.5 However, the question of what constitutes good dietary habits continues to drive debate and has rekindled the low-fat versus low-carbohydrate diet controversy. Nevertheless, weight loss can be achieved by several highly divergent strategies. A recent assessment6 of several different dietary plans found that all demonstrated approximately the same success after one year.

The longer the duration of the diet, the more successful weight loss is.7 Therefore, the best strategy for patients must be a long-term healthy eating plan focused on variety and balance. Very low-fat and very low-carbohydrate diets may be difficult to sustain. In addition, when carbohydrates are restricted to less than 60 g per day, some nutrients will be limited. Restrictive diets that limit a particular food group invariably will reduce not only calories but also nutrients. Dieters who initially follow a very low-carbohydrate diet often will consume more meats and fats rather than include a variety of vegetables in their diets. This approach results in low dietary fiber levels, poor nutritional balance, and possible electrolyte imbalance.

A moderate carbohydrate intake that provides the daily Dietary Reference Intake of 130 g of carbohydrates per day8 will allow more diversity in food selection and a broader nutrient intake. It is important to note that moderately low-carbohydrate dietary plans that eliminate sugar and refined carbohydrates can help establish healthier habits. Total sugar intake is highly predictive of body mass index.9 Steering patients toward the consumption of vegetables, fruits, beans, nuts, and whole grains will help them replace the empty calories of sugar and refined starches.

Whole foods (i.e., foods that are grown and eaten without major changes in nutrient content and that are not highly refined) generally have low glycemic loads.10 Glycemic load rates the blood glucose response to a serving of carbohydrate-containing food. Diets with low glycemic loads promote stabilization of blood sugar levels, normalization of triglyceride levels, higher satiety, and lower food consumption.11 Diets with a low glycemic load also have been shown to reduce the risk of cardiovascular disease12 and type 2 diabetes.13 The quality of foods eaten, whether carbohydrates or fats, may be more significant than the quantity.14

Additional long-term research is needed to determine whether low-carbohydrate diets result in sustainable weight loss. However, any highly restrictive diet is by definition limiting, and any long-term eating plan should include a variety of whole, nutritious foods.

Because of diverse health requirements of our patients and inherent biochemical differences, diets should be tailored to the individual patient. Most importantly, a healthy lifestyle should be encouraged, which means following the time-honored advice of eating wholesome foods, eating in moderation, and exercising regularly.

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