The Zone Diet

views updated

The Zone diet


The Zone Diet program is a food management system that claims to promote optimal metabolic efficiency in the body by balancing the hormones insulin and glucagon. Insulin is responsible for converting, in the blood, incoming nutrients into cells. Glucagon regulates glucose in the liver. The Zone's food plan consists of a dietary intake of 40% carbohydrates, 30% protein, and 30% fat.


In 1995, Dr. Barry Sears, Ph.D., a former biotechnology researcher for the Massachusetts Institute of Technology, authored The Zone. Since that time, the book has sold over one million copies. One of the more popular carbohydrate-restrictive diets , the Zone's success has recently spawned several Zone "knock-off" diets. The Zone Diet is based on a program Dr. Sears developed almost twenty years earlier to treat heart disease in Type 2 diabetics. One of his key inspirations for developing this program was his own genetic history, which demonstrated an inclination for premature heart attack .

In a web interview for WebMD Health, Spending a Week in the Zone with Barry Sears, Ph.D., Dr. Sears explained that he believed that the primary cause of heart disease was not high cholesterol but high levels of insulin; and that the Zone Diet is designed to control insulin levels and thus promote better health. Dr. Sears continues to promote his diet through speeches and his web site,


The name of Dr. Sears' diet refers to an expression used by athletes to describe a euphoric state of optimal physical and mental efficiency. At its heart, the Zone Diet strives to control two metabolic hormones, insulin and glucagons, as well as properly balance eicosanoid metabolism. Eicosanoids, found in fatty acids, are important in the regulation of inflammatory, immunological and hemostatic (arresting hemorrhage) processes. Metabolism is the chemical process in living cells that provides the body with energy and new material to repair waste. In addition to permanent weight loss, this hormonal balance is said to increase longevity and blood flow, improve the immune system, and promote a sense of general well being. Furthermore, the Zone Diet is thought to assist in the prevention of chronic ailments such as diabetes, heart disease, and high blood pressure.


The diet asserts that by controlling the glucagons-insulin ratio in the body, it promotes long-term weight loss as the body burns excess fat. In addition, it is claimed that balancing levels of eicosanoids further increases mental and physical performance and reduces inflammation and hunger. This state of hormonal balance, also referred to as "the Zone," is achieved, according to the diet, by maintaining a dietary ratio of 40% carbohydrates, 30% fat, and 30% protein. It is this dietary ratio that has led people to call the Zone a "40/30/30 diet."

The Zone diet requires eating five times a daythree full meals as well as a mid-afternoon and pre-bed-time snack. The dieter is told that he/she should eat at least once every five hours to maintain proper insulin levels. There are two distinct methods used when preparing a Zone meal: the Eyeball Method and the Block Method. Following either method should provide a daily caloric intake of roughly 1,200 calories for women and 1,500 calories for men.

With the Eyeball Method, the dieter's hand is used to judge portion sizes. For low fat proteins (chicken and fish), the portion should be approximately the size and thickness of the dieter's palm. This equals roughly three ounces of protein for women and four ounces for men. Then carbohydrates are added to the meal. For "favorable" carbohydrates, such as most fruits and vegetables, two loose, fist-sized portions may be added. For "unfavorable" carbohydrates, such as pasta and grains, only one tight, fist-sized portion may be added. Finally, a "dash" of dietary fat is added, which can consist of a few nuts, olives, or guacamole.

The second, and more precise, method for the Zone diet is the Block Method. In this method, each "Zone Food Block" consists of three "mini-blocks," which each represent one portion each of low-fat protein, favorable carbohydrates, and dietary fat. These mini-blocks contain a precise measurement of these macronutrients, specifically seven grams of protein, nine grams of carbohydrates, and 1.5 grams of fat. Each of the three daily meals and snacks consists of a set number of blocks. Women should consume three blocks per meal and one block for each snack, totaling eleven blocks each day. Men should consume four blocks per meal and one block for each snack, totaling 14 blocks each day. These are considered the minimum daily nutritional requirements for an adult. Different factors, such as increased muscle mass and pregnancy , may increase the daily food block requirements.

The Zone diet is only one of four key elements in the entire nutritional program proposed by Dr. Sears. The other three elements are the use of monounsaturated fats, dietary supplementation of Omega-3 fish oils, and exercise . These other elements, it is asserted, will help control metabolic function, produce "good" eicosanoids, and lower insulin levels. These four elements combined should produce a positive hormonal balance and thus increased health and permanent weight loss.


There are few preparations required for going on the Zone diet. However, as with going on any diet, it is wise to consult with a physician beforehand. A physical examination and blood work are suggested, particularly to determine levels of cholesterol, glucose, insulin, and triglycerides (fatty acids). Dieters should also prepare their kitchens by purchasing proper measuring tools and a food scale. In addition, they should empty their cupboards of all foods with high-density carbohydrates. Zone "quick start" kits are also available from various retailers and on-line stores.


Dr. Barry Sears grew up in Long Beach, California, where he exhibited both an athletic and scientific bent. After graduating from Palisades High School at the age of 17, Sears went to Occidental College to major in chemistry. He played both basketball and volleyball in college, and even after he earned his Ph.D. in biochemistry from Indiana University in 1969, he continued to play volleyball at the national level. Sears became keenly interested in understanding heart disease when his father died of a massive heart attack at the age of 53. Within several years, his father's three brothers all also died of heart attacks. This left Sears with a goal to find some way to combat heart disease. He came upon a study published by two researchers at a San Francisco hospital that claimed that arteriosclerosis, or hardening of the arteries, had been cured in rabbits by the injection of naturally occurring fats called phospholipids. Seizing on this one study, he started his own company in 1976, Lipid Specialties, Inc. The aim of Lipid Specialties was to come up with a phospholipid that could be created in the laboratory, and was thus patentable. Sears came up with several "new" phospholipids, and collaborated on animal studies of their effects with the drug manufacturer Upjohn.

After running out of private funding, Sears shifted his study of the effects of phospholipids on heart disease to a new venture: using phospholipid technology to deliver cancer-fighting drugs. Some drugs that were highly effective at shrinking tumors were nevertheless too toxic to help cancer patients unless they could be modified to go directly to the tumor sites. Sears' phospholipids could safely carry new cancer drugs in the bloodstream. He took out several patents for drug-delivery systems using phospholipids.

But Sears' interest veered again with the awarding of the Nobel Prize for Physiology and Medicine in 1982 to three researchers who had uncovered the functioning of a class of hormones known as eicosanoids. Eicosanoids control a variety of systems within the body, including the cardiovascular system, the immune system, and the body's system for regulating fat storage. The fatty acids Sears had been studying for years in his lipids work were also the building blocks of the eicosanoids. At this point Sears made a leap from biochemical research to nutritional science. He deduced that many diseases could be traced to an imbalance of eicosanoids. The best way to regulate eicosanoids, he theorized, was through food. In the early 1980s, Sears elaborated a theory of nutritional control of eicosanoids that evolved into the Zone diet.


As every individual possesses a unique biochemistry, achieving "the Zone," the state of optimal mental and physical efficiency, can be very subjective. This subjectivity can lead to confusion and frustration as individuals attempt to find their perfect metabolic balance using the 40/30/30 diet plan. Some critics believe the Zone diet is too strict, making it too difficult to maintain over a long period of time.

Due to its high protein ration (30%), the Zone diet is not recommended for people with impaired liver or kidney function. Protein metabolizes in the liver and is then excreted by the kidneys. The added strain of a high protein diet can cause long-term damage to these organs, as well as cause kidney stones and bone loss. Some experts further believe that these high protein requirements also contra-indicate the Zone diet for people with or at risk of heart disease, due to the higher level of saturated fat and cholesterol in many high protein foods. Clinical studies have shown that high fat/high protein/low carbohydrate diets can also increase the risk of serious diseases such as high blood pressure, stroke , and adult-onset diabetes.

Despite Dr. Sears' claims to the contrary, many scientific studies show that the Zone diet may actually impair physical performance rather than enhance it. Fatigue experienced by athletes during exercise may be due to the diet's low proportions of dietary intake of carbohydrates (as stated above) as well as inadequate caloric intake. Additionally, the suggested benefits of risk reduction and increased health may be overstated.

Side effects

Dr. Sears states there are few or no side effects associated with his diet. However, many nutritional experts disagree. The Zone diet requires an intake of carbohydrates below the minimum nutritional daily requirements (100120 g) agreed upon by most health experts. This deficiency can lead to several health risks such as cardiac problems, ketosis, and orthostatic hypotension (temporarily lowered blood pressure, usually from standing up quickly, causing temporary blood flow reduction and lack of oxygen to the brain, then lightheadedness and sometimes loss of consciousness). Mineral and vitamin deficiencies caused by low carbohydrate consumption may increase the risk of numerous diseases. The diet's high protein intake places added stress on kidney functions, increasing the risk of gout, osteoporosis , kidney stones, and kidney damage. One researcher, Sachiko St. Jeor, and colleagues concluded that dieters following diets like the Zone are potentially at risk for vitamin and mineral deficiencies.

Research & general acceptance

Although the Zone diet is not as strongly criticized as most high protein/low carbohydrate diets, few health organizations and nutritionists endorse it. Indeed, organizations such as the American College of Sports Medicine and the American Dietetic Association have publicly disagreed with the 40/30/30 plan. Most experts note the Zone diet's lack of scientific credibility, either claiming that the majority of Dr. Sears' observations and findings are supported by poorly controlled studies, unproven theories, non-validated results, and half-truths, or that the majority of published scientific research points to the detrimental effects of the Zone rather than to its health benefits. The long-term effects of the Zone diet have not been fully researched; therefore, the diet's long-term health benefits and risks are still undefined.

Training & certification

There is no formal training or certification required for the Zone diet. As Dr. Sears stated, "All you need [to start on the diet] is one hand and one eye."



Sears, Barry. The Zone. New York: Harper-Collins, 1995.

Sears, Barry. Mastering the Zone. New York: Regan Books, 1997.


Cheuvront, Samuel. "The Zone Diet and Athletic Performance." Sports Medicine (April 2000): 289294.

Cheuvront, Samuel. "The Zone Diet Phenomenon: A Closer Look at the Science behind the Claims." Journal of the American College of Nutrition (February, 2003): 917.

Coleman, Ellen. "The BioZone Nutrition System: A Dietary Panacea?" International Journal of Sports Nutrition (March, 1996): 1921.

Jarvis, Mark, Alan Seddon, Lars McNaughton, and Dylan Thompson. "The Acute 1-Week Effects of the Zone Diet on Body Composition, Blood Lipid Levels, and Performance in Recreational Endurance Athletes." The Journal of Strength and Conditioning Research. (February 2002):5057.

Kendall, Pat. "Zoning in on the Zone." Nutrition News (September 1997).

St. Jeor, Sachiko, Barbara Howard, Elaine Prewitt, Vicki Bovee, Terry Bazzarre, and Robert Eckel. "Dietary Protein and Weight Reduction." Circulation (October 2001): 18691874.


Babal, Ken. "The Zone: Sound Advice or Just Another Diet?" [cited June 13, 2004]. <>.

"Introduction to the Zone." Zone Perfect [cited June 13, 2004]. <>.

McDougall, John. "The Great Debate: High vs. Low Protein Diets" [cited June 13, 2004]. <>.

Sears, Barry. "Zone Diet." [cited June 13, 2004]. <>.

"Spending a Week in the Zone with Barry Sears, Ph.D." WebMD Health [cited June 13, 2004]. <>.

"The Zone Diet." [cited June 13, 2004]. <>.

"The Zone Diet." Weight-loss Institute [cited June 13, 2004]. <>.

Lee Ann Paradise