Nearly everyone knows at least one person who has tried one of today's best-selling high-protein, low-carbohydrate diets; for some, it encompasses their whole circle of friends. Often, it mirrors the domino effect—one person tries the diet, loses a bunch of weight, and all of her friends can't wait to jump on the protein bandwagon.

For example, Marie says she lost 10 pounds on the high-protein diet advocated by Michael and Mary Eades in Protein Power (Bantam Books). And she wouldn't hesitate to do it again. "It took away the lows and highs of my regular diet where I absolutely had to eat now or I'd feel rotten," she says. "I like this diet for that very reason."

Then there's Michael, who combined Dr. Atkins' New Diet Revolution (M. Evans & Co., Inc.) with an exercise program for two months and lost 30 pounds. He says the program made him realize how carbohydrate-heavy his diet was, and since losing the weight, he is now motivated to eat better. Even so, he's now abandoned the protein regimen. "I wasn't willing to commit to the fundamental lifestyle change the Atkins diet demands," he explains. "I love things like fruit too much. And I was craving carbs too much."

Millions of Americans have bought into these high-protein plans. In the wake of their popularity, however, people are confused about how much protein they really need. And many mainstream health and nutrition experts remain wary of these diets. They worry about the health hazards of eating a high-protein diet (which often translates into high-fat) for an extended period of time.