South Beach diet
Illustration: Edwin Fotheringham
Americans spend $60 billion a year on diets, pills, and programs in the hope that the weight loss approach they choose will ultimately triumph over others. Although there are many diets in contention, a clear winner has yet to emerge. As obesity rates continue to rise dramatically worldwide, scientists have recognized the need to test the effectiveness of the most widely used plans. Over the past two years, three notable university-based studies (one from Stanford, a second from Harvard and the Ben-Gurion University of the Negev, and a third from the University of Missouri) have pitted some of the leading diets against one another—and, in the last case, against exercise—to determine which approach offers the best results. Their conclusions may surprise you, so before you spend any more money or time fretting over the most recent diet aid, check out the results of the matchups.

The Contenders:

Atkins dietLow Carb (e.g., Atkins)
Advises lots of protein, mostly in the form of meat at every meal, and restricts carbohydrates. Thirty percent of your calories will come from protein, 50 percent from fat, and about 20 percent from carbs, especially good ones like veggies and fruit.

Strawberry Low Fat (e.g., Weight Watchers)
Emphasizes grains, fruits, and vegetables and allows modest servings of meat. Portion control is key. About 50 percent of your calories will come from carbohydrates, 30 percent from fat, and 20 percent from protein.

Zone diet Zone

Balances carbohydrates, fat, and protein, theoretically to stabilize hormones that trigger hunger and weight gain. Thirty percent of the calories you eat will be fat, 40 percent carbohydrates, and 30 percent protein.

Mediterranean diet Mediterranean

Prescribes grains, vegetables, and sources of healthy fats such as olive oil and nuts. About 45 percent of your calories on this plan will come from carbohydrates, 35 percent from fat, and 20 percent from protein.

Ornish diet Ornish

Is an extremely low-fat vegetarian diet that recommends forgoing nuts, meat, and fish. Roughly 70 percent of your calories will come from carbohydrates, 20 percent from protein, and 10 percent from fat.