Cutting down on carbs may help people lose weight, but it may not be so good for lowering cholesterol, new research shows.

People who ate a diet low in carbohydrates but relatively high in fat lost the same amount of weight over six weeks as those who consumed a high-carb diet.

But levels of low-density lipoprotein (LDL) or “bad” cholesterol increased significantly in the low-carb group, while they fell in the high-carb group. High LDL levels are a risk factor for heart disease because they are linked to clogged arteries.

Low-carb diets have become increasingly popular in recent years, and proponents claim they may be more effective for reducing diabetes risk and cholesterol levels, Dr. Teri L. Hernandez of the University of Colorado at Denver in Aurora and her colleagues write in their report in the American Journal of Clinical Nutrition.

But little is actually known about how these diets compare with higher-carb weight loss plans in terms of these effects, they add.

To investigate the effects of diet on these measures during active weight loss, Hernandez and her team randomly assigned 32 obese adults to follow a low-carbohydrate diet, including 20 grams of carbohydrate or less daily, or a high-carb diet with 55 percent of calories coming from carbohydrates for six weeks.

Both groups lost around 6 kilograms (13 pounds). But the individuals on the low-carb diet actually had an average increase of 12 milligrams per deciliter increase in their LDL levels, up from 109 milligrams per deciliter (less than 100 is considered optimal); the high-carb diet group showed a 7 milligram per deciliter decrease, down from 102.

The low-carb group also showed greater increases in their levels of free fatty acids, which are released into the blood when the body breaks down stored fat. High levels of free fatty acids make it more difficult for the liver to store glucose, which in turn ups sugar levels in the blood. Consistently high sugar levels define diabetes.

“These data suggest that a high-fat diet may have adverse metabolic effects during active weight loss,” Hernandez and her team conclude.

SOURCE: American Journal of Clinical Nutrition, online January 27, 2010.