People made fun of it for years, but now the Atkins diet is wildly popular.

For the first time, a look at all the research on the diet is revealing the good and bad effects of the Atkins approach.

MORE ON THIS STORY The Lancet American Heart Association Diet Info

When Frank Long, 41, stuck to his Atkins-type high-protein, low-carbohydrate diet for a year, he shed 95 pounds.

"Actually I haven't felt better since I was in my 20s," he said.

The Atkins diet approach now tried by millions allows unlimited consumption of protein and fat but severely limits carbohydrates.

A review of 60 studies on the Atkins approach reveals some benefits but also worrisome side effects.

At six months, Atkins dieters lost as much body fat as those on low-calorie, low-fat diets. And in the short term they lost more weight and some had better cholesterol improvement.

But after a year the two types of dieters had about the same weight loss.

Even so, the Atkins dieters had endured more side effects such as headaches, muscle weakness, and constipation or diarrhea.

Local weight loss specialist Dr. Robert Kanter says the findings show Atkins is safe for some.

"For use over six months, there does not appear to be any adverse effect on the heart or on people's general health if they don't have osteoporosis, kidney stones or diabetic kidney disease," Dr. Kanter said.

But he says the new research reinforced that weight loss comes down to calories.

"It didn't matter what the carbohydrate content was. What was critical was how long they stayed on the diet and how much they restricted their calories," he said.

No one knows yet the very long-term health effects of the Atkins diet. We continue to follow for you the research that will provide answers.