A study in New England Journal of Medicine finds low-fat diets do not work unless you get off the couch and exercise as well.

The authors of the yearlong study tried various combinations of diet and exercise on 377 men and women who had too much "bad" cholesterol and too little "good" cholesterol.

Nothing seemed able to significantly raise the levels of "good" cholesterol. A low fat-low cholesterol diet brought down the levels of "bad" cholesterol to some degree, but the only significant difference was seen in people in the group using diet combined with vigorous exercise.

"The reductions in LDL (bad) cholesterol levels were not significant for either sex without the addition of exercise," said the research team, led by Marcia Stefanick of the Stanford University School of Medicine.