Discovery Health: People trying to lose weight often say they've had limited or no success following the 20-20-60 diet. Consumer magazines praise the "high-protein low-carbohydrate" diet as a panacea for the American weight problem. Your views?

Dr. Shike: These "high-protein, low-carbohydrate" diets have not been proven to be safe or effective in the long run. We know, for example, that high-protein diets may be harmful to the kidneys, and are associated with calcium loss, which can result in bone problems.

Also, an extreme diet of any kind—say, one high in meats and whole-milk dairy products—may be harmful because high-fat diets have been associated with a number of chronic diseases, including cancer and heart disease. Also, when a whole class of foods is restricted, critical nutrients may be lacking from the diet.

In a fat-rich, low-carbohydrate diet, the body switches to a form of metabolism that produces ketones. The presence of ketones in the blood system causes the blood to become acidic. Persistent acidity can lead to nausea, muscle breakdown, headaches, irritability, kidney problems and weak bones. Another problem with the low-carbohydrate diets is that they may be deficient in essential nutrients such as calcium, potassium and various vitamins.

Discovery Health: A number of books on the market virtually guarantee weight loss simply by adjusting the percentages. "Raise the protein, lower the carbs," as it were.

Dr. Shike: It's true that consuming high-protein or high-fat diets may initially induce weight loss in some people. But what has to be understood is that weight loss is based on calorie restriction—not on what is being consumed!

Fad diets prohibit a lot of foods—in the case of high-protein diets, carbohydrate intake is severely restricted. And guess what? People lose weight not because of the altered food balance, but simply because they are restricting calories. Of course they will lose weight!

Now, if you are going to restrict calories—which is vital to losing weight—isn't it better to restrict them in a way that is consistent with a healthy diet? Nobody needs excess protein and fat in their diets for the many health-related reasons we have already discussed.

Although the potential negative effects that I mentioned earlier may take some time to become apparent, it is important to understand that the long-term safety of these fad diets has not been established.