By Maureen Callahan, M.S., R.D.
Updated: April 18, 2008

Athletes fondly dub it “the Zone.” But author and biochemist Barry Sears, PhD, says dieters can enter this near-euphoric state of maximum performance, too. The key, in a word, is food. Eating a precise combination of protein and carbs at meals places you in a metabolic “zone” in which fat loss becomes automatic and hunger is kept at bay. First introduced in 1995, the Zone regimen has taken a few twists and turns in light of new research about disease-fighting foods such as soy (The Soy Zone, 2000) and pharmaceutical-grade fish oils (The OmegaRx Zone, 2002), as well as the health-compromising effects of blood vessel inflammation (The Anti-Inflammation Zone, 2005). But essentially, the premise of eating to stay “in the Zone” is still the same.

Sears may say his diet doesn't require a "great deal of unrealistic self-sacrifice," but the whole notion of achieving a precise balance of protein and carbs at each meal could be one big headache for many folks. Calorie counting it ain't, yet you need a keen knowledge of portion sizes and nutrient profiles to keep in the Zone-and that's going to take a lot of work. Another big problem: The whole strategy is based on a shaky scientific foundation. There's no proof that food puts dieters in the Zone or that being there promotes weight loss. It's probably the diet's low calorie level that peels off the pounds.

Basic principles:

Calorie counting is out. But dont throw away the calculator or scales. The cardinal rule of the Zone is maintaining the ideal ratio of protein to carbohydrates at each meal. Why so precise? Blame it on hormones. According to Sears, the major nutrients—fat, protein, carbs—each trigger a complex set of hormonal responses in the body. Eating the right foods at the right time keeps these hormones, insulin in particular, in a favorable balance.

How the diet works:

Food is treated like a drug, eaten in a controlled fashion and in precise portions. The ideal plan is to divide the day into three daily “Zone-friendly” meals and two “Zone-friendly” snacks. In the end, the nutrition profile is comparable to that of many other popular low-carb diets: 40% carbs, 30% fat, and 30% protein.

What you can eat:

Palm-size portions of lean meat, seafood, tofu, fruits, and vegetables are all OK. But you need roughly equal amounts of carbs and protein at each meal. To make things simple, Sears translates these nutrients into “blocks” so that dieters can achieve the right mix of the two. Complex carbs like whole-grain bread and brown rice are favored over simple processed carbs like white bread and white rice.

Does the diet take and keep weight off?

No more or less than many other popular plans. At least that's the word from researchers at Tufts-New England Medical Center in Boston who randomly assigned 160 overweight volunteers to one of four weight-loss regimens: Atkins, Dean Ornish, Weight Watchers, and The Zone. After one year, average weight loss among participants was a modest 5 percent regardless of the program. Sears presents his own findings, however. In a 6-week study of 91 slightly overweight volunteers, women who followed the diet lost an average of 7 pounds of fat, and their overall body-fat percentage dropped from 29 percent to 26 percent. Men lost an average of 3 pounds of fat and dropped from 20 percent to 17 percent body fat.

Is the diet healthy?

It's not certain. The fact that the Zone promotes monounsaturated fats like olive oil, olives, and peanuts, as well as the omega-3 fats found in fish oils, is good. And 30 percent of calories from fat is a moderate, realistic approach that the federal government and health organizations like the American Heart Association have long promoted. The unclear part: 30 percent protein is a little higher than most health organizations recommend. And 40 percent carbs is a little lower than advisable. Without long-term data on the health effects of low-carb, high-protein diets, there's no absolute guarantee of safety.

What do the experts say?

Registered dietitian Pat Kendall, PhD, a food scientist and human-nutrition specialist with Colorado State University's Cooperative Extension, thinks the Zone is a mixed bag. "It promotes eating regular meals, which is good," Kendall says. "And it's low enough in calories to promote weight loss. But it's too low in calories to serve as a long-term diet regimen." She finds it alarming that Sears eats only 1,332 calories per day to stay in the Zone. "Thirteen hundred calories is considered a low-calorie diet even for a small woman," Kendall says. "It's a very low-calorie diet for Sears, who clocks in at 6 feet 5 inches tall and weighs 210 pounds." What about the whole hormone-Zone philosophy? Unproven. Like a lot of the low-carb diets, the Zone relies on "poorly controlled, non-peer-reviewed studies, anecdotes, and nonscience rhetoric," reports Samuel N. Cheuvront, PhD, RD, of the U.S. Army Research Institute of Environmental Medicine in Natick, Massachusetts. Cheuvront, who just published an in-depth review of the Zone for the Journal of the American College of Nutrition, concludes that the protein-carb ratio the diet supports has no basis in scientific fact and that Sears "selectively ignores the known effects of macronutrients and hormones that contradict the Zone theory." In other words, there are a lot of holes in Sears' philosophy.

Who should consider the diet?

Number crunchers might get a kick out of keeping such close tabs on protein and carbs. The diet is not recommended for people with kidney problems; a large amount of protein in the diet can overtax kidneys.

Bottom line:

Even though the Zone philosophy may be more rhetoric than scientific fact, the plan has some good points. It offers a healthy approach to fat. It's also laudable that Sears emphasizes lean proteins and encourages plenty of fruits and vegetables. It's just too little food once you've shed the pounds. After reaching their weight-loss goals, dieters need to increase portions slightly.
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