Four Popular Diets: Which Is Best?

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Dansinger MG, Gleason JA, Griffith JL, et al.: Comparisons of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: A randomized trial. JAMA 293:43-50, 2005.

What is the problem and what is known about it so far?

Obesity is a growing problem in this country. Doctors and patients want to know the best diets for losing weight and lowering the risk of heart disease. There are more than 1,000 diet books available. So it's hard to know which diets are safest and work best.

Who was studied?

Researchers studied adults who were overweight or obese, with a body mass index (BMI, a measure of weight in relation to height) between 27 and 42. They had at least one risk factor for heart disease -- such as high cholesterol, or amount of fat in their blood, low "good" cholesterol (HDL), or high blood pressure. Some people were in the study because they were on medication for high blood pressure, type 2 diabetes, or blood lipid (fat) problems. People taking insulin were not included in the study. A total of 160 people were studied for up to 1 year.

How was the study done?

People were put in groups where they went on one of the following diets: Atkins, Zone, Weight Watchers, or Ornish. A doctor and a dietitian gave them cookbooks and other information about the diet they were to follow. During the first 2 months, all the groups met four times to support and encourage each other. Everyone kept track of the food they ate.

The Atkins group tried to eat fewer than 20 grams of carbohydrate daily, gradually moving up to 50 grams. The Zone group tried to balance their calories: 40% from carbohydrate, 30% from fat, and 30% from protein. The Weight Watchers group tried to eat 1,200-1,600 calories each day. The Ornish group tried to stick to a vegetarian diet with only 10% of calories coming from fat.

What did the researchers find?

Many people dropped out of the study. By the end of the year, 48% of the Atkins group, 35% of the Zone group, 35% of the Weight Watchers group, and 50% of the Ornish group had quit. Most people who quit said their diet was too hard or they didn't lose enough weight.

People on all four diets lost weight at the end of 1 year. About 25% lost 5% of their body weight. Ten percent lost more than 10% of their body weight.

People on all the diets except Atkins had lower LDL (“bad”) cholesterol at the end of 1 year. And people on all the diets except Ornish had higher HDL ("good") cholesterol. None of the diets reduced the level of fat in people's blood (triglycerides), lowered their blood pressure, or lowered their fasting glucose (blood glucose more than 4 hours after a meal).

None of the diets made people's risk factors for heart disease worse.

What were the limitations of the study?

Studying a larger number of people would be better in order to find the "best" diet. And a longer study would be better because researchers could learn whether people had health problems due to the diets. Also, people in the study kept track of their own meals, so it's not clear how well they stuck to their diet.

What are the implications of the study?

We need better ways to help people stick to a diet -- and to match people with the diet that is best for them.