The Zone Diet Analyzed

Madonna, Jennifer Aniston and Demi Moore are among its fans. Is it just a fad, or does it really promote healthy weight loss?

By Dulce Zamora
WebMD Weight Loss Clinic - Feature

Reviewed By Michael W. Smith, MD

As if dieting wasn't challenging enough, the sheer number of fat-buster guides out there may be reason enough to just forget the whole thing. But, alas, the unforgiving mirror or those too-tight jeans serve as good reminders of the pudgy enemy. So onward the march to join the infamous fight against flab.

One of the more popular weapons of choice has been a program that claims to use food as a drug for overall good health, weight loss, and the prevention or management of heart disease and diabetes. In the book The Zone, Barry Sears, PhD, explains how the right ratio of carbohydrates to proteins and fats can control levels of insulin in the bloodstream. Too much of the hormone, he says, can increase fat storage and inflammation in the body -- conditions that are associated with ailments such as obesity, type 2 diabetes, and heart disease.

Sears' theories resonate with a significant number of people who become devotees of The Zone Diet. Many of them enthusiastically talk about "40-30-30," and about "being hormonally correct."

To the outsider, it may seem as if they have gone off to some other zone, but some health experts say the plan may produce good health and weight loss for some people. The Zone's recommendations supposedly don't stray far from the USDA's dietary guidelines.

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.

Sears questions the AHA's view of The Zone. "It's hard to be a high-protein diet when you're actually consuming more carbohydrates," he says. "The Zone Diet is really a low glycemic-load diet that has adequate protein. You're looking to balance protein to carbohydrates to get the right balance of various hormonal parameters, particularly the hormone insulin."