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Weighing In on Low-Carb Diets

The Diet Debates

With obesity rates soaring, scientists continue the debate over what kind of diet is most effective for long-term weight loss. Proponents of low-carb, high-protein diets maintain that they promote more weight loss than low calorie, low-fat diets, and that they favorably impact blood sugar and insulin levels (linked to diabetes). Others argue that cutting calories and exercising is the real key to shedding pounds that will stay off longer. Many are also concerned that the long term safety of low-carb diets hasn't been determined.

A 2003 review of over 107 weight loss studies failed to settle the debate (1). The good news, though, was that low-carb diets didn't adversely affect blood pressure, glucose or cholesterol levels. Now, two recent studies comparing "Atkins-style" versus conventional diets - the longest trials conducted so far - help clarify the issue.

New Evidence Sheds More Light

The first trial (2), lasted 6 months and involved 120 overweight adults with high cholesterol levels. The low-carb diet (20 g of carbs: unlimited calories, animal foods and eggs, 4 oz. of hard cheese, 2 cups salad vegetables, 1 cup low-carb vegetables, multivitamin), produced more weight loss and greater reduction in body fat than the low-fat, low calorie group (reduced fat, 500-1000 less calories per day, multivitamin). It also appeared to be an easier diet to stick with, as there was less participant drop out (76% of the low-carb dieters completed the study compared to 57% on the conventional diet). The low-carb dieters experienced better changes in their triglyceride and HDL levels, though changes in so-called "bad" LDL cholesterol were no different in the two diets.

After 1 Year: Similar Weight Loss, Lower Risk

The second (3), year-long trial followed 132 obese adults counseled to restrict daily carb intake (30 g or less), or to cut calories by 500 and keep fat to less than 30% of total calories. Both the low-carb and conventional dieters lost a similar amount of weight at the end of the year. However the findings on blood fats were consistent with those from the first study: better triglyceride and HDL levels for the low-carb dieters. The study also included about 50 people with diabetes. Diabetics who restricted carbs appeared to have better blood sugar control, though there were too few subjects to draw firm conclusions.

"We can no longer dismiss very low-carbohydrate diets", according to Harvard School of Public Health's Dr. Walter Willett. "We can encourage overweight patients to experiment with various methods of weight control, including reduced carbohydrate diets, as long as they emphasize healthy sources of fat and protein and incorporate regular physical activity", he concluded in an editorial. In terms of safety, the authors don't recommend low-carb diets for those attempting first time weight loss, and warn that people with a history of gout or kidney stones, diabetics, or people with high blood pressure using diuretic drugs should not begin low-carb diets without close medical supervision.

Are "Low-Carbs" Right For Everyone?

If you've already embraced low-carbs, these findings should be reassuring. Aside from weight loss though, experts question whether low carb represents healthful long term eating. For example, extra protein in the diet crowds out fruits and vegetables - foods which have been shown to prevent many types of cancer. Americans do eat far too many sugary and processed carbs. But many of us can get back on track by cutting out junk foods, sticking to reasonably sized portions of healthy carbs (whole grains), eating more omega-3 fats (fish), and moving more everyday. For those that do try carb-restricted diets, keep in mind that they can be low in fiber, calcium and vitamin D (milk), antioxidants (e.g. C and E from fruits/vegies), and possibly the B vitamins (fortified grains). So remember to close these nutritional gaps with appropriate supplementation.

References

1. Bravata DM, et al. Efficacy and safety of low-carbohydrate diets: a systematic review. JAMA 289:1837-50, 2003.
2. Yancy WS, et al. A low-carbohydrate, ketogenic diet versus a low-fat diet to treat obesity and hyperlipidemia: a randomized, controlled trial. Ann Intern Med 140:769-77, 2004.
3. Stern L, et al. Effects of low-carbohydrate versus conventional weight loss diets in severely obese adults: 1year follow-up of a randomized trial. Ann Intern Med 140:778-85, 2004.