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Is a low-carbohydrate diet the best diet for metabolic syndrome? Restricting carbs also lowers calorie intake.

The increase in obesity in the United States over last 30 years parallels an increase in carbohydrate consumption over the same time period, data from the National Health and Nutrition Examination Survey (NHANES) show.

I became interested in studying low-carbohydrate diets when my patients introduced me to popular diet books. Having a health care provider tell a patient to look at a book can have a dramatic motivating effect. Although we are still awaiting data from large-scale clinical trials of low-carbohydrate diets, the results from studies over a 6- to 12-month period are quite remarkable.

Low-carbohydrate ketogenic diets--defined by a reduction in carbohydrate to 20-50 g/day--produce greater weight loss, triglyceride reduction, and HDL cholesterol elevation than does a 30% low-fat diet across several studies (Arch. Intern. Med. 2006;166:285-93). In most studies, low-carb diets result in an improvement in the components of the metabolic syndrome by reducing abdominal girth; lowering triglycerides, glucose, and blood pressure; and raising HDL cholesterol.

An important point about low-carbohydrate diets and serum lipids is that if you look only at LDL cholesterol, especially when calculated by the Friedewald equation, you might conclude that there is no benefit for cardiac risk reduction because the LDL cholesterol level doesn't change significantly. However, if you look at lipid subfractions, small LDL cholesterol is improved with both a low-fat and a low-carbohydrate diet, in addition to the other improvements in the metabolic syndrome.

What is the latest evidence regarding how low-carb ketogenic diets work? The best data are from Dr. Gunther Boden's metabolic ward study comparing a low-carbohydrate diet with a conventional diet (Ann. Intern. Med. 2005;142:403-11). In this study, appetite suppression on the low-carb ketogenic diet led to a reduction in calorie intake, and to subsequent weight loss. Study participants reduced their calorie intake from a mean 3,111 kcal/day to 2,164 kcal/day, even though calories were never mentioned in the instruction.

What is novel about the approach is that even without the explicit mention of calories, appetite suppression occurs by the restriction of carbohydrates. It's just another method of achieving a reduction in caloric intake.

In another recent, well-publicized study that compared diets with various carbohydrate and fat levels, investigators found that a greater reduction in weight, body mass index, waist-to-hip ratio, triglycerides, and systolic and diastolic blood pressure, as well as a greater elevation in HDL cholesterol, with the lowest-carbohydrate diet (JAMA 2007;297:969-77).

Before insulin became available around 1920, a low-carbohydrate diet was the preferred recommendation of physicians to treat diabetes. In a study we presented at the American Diabetes Association last year, a low-carbohydrate, ketogenic diet led to a significant reduction in hemoglobin Ale in patients with type 2 diabetes. All patients taking insulin were able to reduce or eliminate their insulin use. It can be a powerful effect.

Some practitioners take a stepwise approach to carbohydrate restriction. In North Carolina, for example, one common source of calories is sugar in sweet tea and other sugar-sweetened beverages. I have people write down everything they eat for my review. If you do this, you'll be amazed by what they're eating.


DR. WESTMAN directs the Lifestyle Medical Clinic at Duke University in Durham, N.C. He has received research funding from the Dr. Robert C. and Veronica Atkins Foundation.
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Title Annotation:Point/Counterpoint
Author:Westman, Eric
Publication:Family Practice News
Article Type:Clinical report
Date:Jul 1, 2007
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