Zone Diet Analyzed: Fad or Healthy Weight Loss? (cont.)

So where does The Zone stand among other popular diet plans? WebMD asked Sears and a couple of health experts.

The Zone's Boundaries

In The Zone, Sears writes that you can better regulate your metabolism with a diet of 40% carbohydrates, 30% protein, and 30% fat (now widely known as the 40-30-30 plan).

In a recent conversation, however, the diet's founder says he rues the day he specified those exact figures. Rather, he would prefer to give a range for better hormonal balance. Everyone is different, he says, and there's no magical percentage for all in managing insulin levels.

"The Zone is a diet that contains no more than 30% of calories from fat, the amount of protein ranges from 25% to 35%, and the amount of carbohydrates ...would be between 35% and 45%," says Sears.

The diet does not prohibit any foods, but severely restricts those high in fat and carbohydrates such as grains, starches, and pastas. Fruits and vegetables are the favored source of carbs. Protein is limited to low-fat fare that's no bigger and no thicker than the palm of one's hand. And as far as fat is concerned, monounsaturated fats such as olive oil, canola oil, almonds, macadamia nuts, and avocados are preferred over other kinds of fats.

For a simple interpretation of The Zone, Sears suggests filling one-third of a plate with low-fat protein, and then piling the rest with fruits and vegetables. You may choose to add a monounsaturated source of fat such as olive oil.

To then determine whether a meal is hormonally correct, Sears offers the following test: "Eat a meal and see how you feel four hours later. If you have no hunger and you have peak mental acuity, the composition of the meal was hormonally correct for your biochemistry."

The American Heart Association (AHA) classifies The Zone as a high-protein diet, and has issued an official recommendation warning against such programs. The statement says such diets are not proven effective for long-term weight loss, and could actually be hazardous to health because they restrict intake of essential vitamins and minerals present in certain foods.

Although The Zone does not ban any type of food, the organization still frowns upon what it considers as the diet's flawed ratio. "If the protein's too high -- even if the fat is just right -- the carbohydrate [portion] must be too low in regards to evidence-based recommendations," says Robert H. Eckel, MD, the AHA's chair of the Council on Nutrition, Physical Activity, and Metabolism.

For healthy living and weight loss, the AHA recommends that daily calories come from 15% to 20% protein, 30% to 35% fat, and the rest from carbohydrates (about 50%). Eckel says the AHA's guidelines are based on scientific research, and are similar to those of other major health groups such as the USDA, the American Dietetic Association, the American Diabetes Association, and the American Cancer Society.