Most professional health organizations, such as the American Heart Association and the American Cancer Society, recommend you eat 55 to 60 percent of your daily calories from carbohydrates, 10 to 15 percent from protein and 25 to 30 percent from fat.

But the authors of today's popular protein plans say that carbohydrate-laden pyramid is what's making us fat. Their theory is this: If you eat too many carbohydrates, your body produces too much insulin. And if you have too much insulin in your system, you will store more fat.

In February, two studies were released that showed the Atkins diet to be a safe and effective way to lose weight. Researchers at the Durham Veterans Affairs Medical Center in North Carolina found that average, mildly obese people who followed the diet lost about 21 pounds in four months and had positive changes in heart risk factors such as reduced LDL ("bad") cholesterol and increased HDL ("good") cholesterol. These results were supported by a second study from researchers at the Atkins Center for Complementary Medicine in New York City. Researchers plan to continue the study in order to monitor the long-term effects of the diet.

Therefore, researchers recommend a diet lower in carbohydrates and higher in protein and fat. These plans appeal to dieters not only because they promise quick weight loss but also because they allow us to eat practically all the red meat, eggs and cheese we want — foods we've been told to limit. Dieters also may find they're not as hungry when they eat more protein. That's because the body breaks it down more slowly than carbohydrates.

For the most part, people do at first lose weight quickly on these diets. But much of that initial weight loss is water, says Ruth Kava, nutrition director for the American Council on Science and Health. That's because carbohydrates are stored in our cells as glycogen, which is what our bodies use for quick energy. With every molecule of glycogen, our bodies also store a certain amount of water.

When you restrict carbohydrates, the body's store of glycogen and water are depleted, says Janis Jibrin, M.S., R.D., author of The Unofficial Guide to Dieting Safely (Macmillan USA). "With a 10-pound weight loss," she explains, "easily half of that could be water."

Decreasing the amount of carbohydrates we eat isn't a bad idea, says Lisa Hark, Ph.D., R.D., director of the Nutrition Education and Prevention Program at the University of Pennsylvania School of Medicine in Philadelphia. But increasing protein and fat isn't the sole answer.

According to the National Health and Nutrition Examination Surveys (American Journal of Clinical Nutrition, 1997, vol. 66), Americans today are eating 220 more calories a day than in 1970. Those extra calories are being consumed from carbohydrates. "Whole grains are obviously carbohydrates," says Hark. "But they're an excellent source of fiber and B vitamins, and cutting them out doesn't make sense. But cutting down on them does."