Too many questions remain unanswered regarding the long-term effects of low-carbohydrate diets for doctors to recommend them to their patients, according to a report in The Lancet.

“Patients who want to try these diets should be told that, although safety cannot be guaranteed, they seem to be safe for short-term use (up to six months) as long as weight loss occurs,” Dr. Arne Astrup and colleagues, from RVA University in Copenhagen, write.

According to their review of low-carbohydrate diets, only three studies have reported on diets sustained for more than 90 days. There was greater weight loss with a low-carbohydrate diet after six months than with low calorie diets. However, in the two studies that were extended to 12 months, there was no difference between the two types of diets.

What is needed, Astrup’s group notes, are studies lasting long enough to assess the diet’s effects on risk factors for heart attack and stroke, such as cholesterol levels.

More information is also needed regarding fiber and micronutrient composition, as well as effects on markers of kidney and bone health, nutritional adequacy, dietary compliance, quality of life and cancer risk.

Until then, the preponderance of scientific evidence is that for people who want to lose weight and keep it off, the best recommendation is a “permanent switch to a diet reduced in calories and fat in combination with physical activity.”

SOURCE: The Lancet, September 4, 2004.