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The Zone diet is a high protein, low carbohydrate diet. It is based on the concept that if people eat an ideal balance of carbohydrates, proteins, and fats at every meal and snack, they will achieve hormonal balance. This will control insulin levels and result in weight loss and health benefits.
The Zone diet was developed by Barry Sears. Sears has a Ph. D. in biochemistry, but no special training in nutrition. He began working on this diet in the 1970s. After his father died prematurely of a heart attack at age 53, Sears began studying the role of fats in the development of cardiovascular disease. In 1995, his book Enter the Zone, became a bestseller. Since then he has written a dozen books and cookbooks about the Zone diet, established a Web site, and developed a program of home-delivered Zone meals, turning the Zone diet concept into a multi-million dollar business.
The Zone diet is designed to promote fat loss and weight loss, but its developer also claims that the diet brings about substantial health benefits. This diet is highly structured. Participants in the Zone diet are instructed that every meal and every snack should consist of 40% carbohydrates, 30% protein, and 30% fats. This produces what Sears considers the ideal ratio of protein to carbohydrate. The protein to carbohydrate ratio of .75, Sears says, allows the body to function at optimal level. He refers to this optimal functioning as being “in the Zone.” Being in the Zone claims TO boosts energy, delays signs of aging, helps prevent certain chronic diseases and allows the body to function at peak physical and mental levels. The Zone diet is less concerned with people reaching a specific weight than with reducing body fat. The goal is for men to have only 15% body fat and women 22% body fat.
The amount of food a Zone dieter consumes is based on that person's protein needs. Protein needs are calculated based on height, weight, hip and waist measurements, and activity level. The amount of carbohydrates and fats allowed on the diet derives from the calculation of protein needs. The result is a daily diet that usually ranges from 1,100–1,700 calories. Dietitians consider this a low calorie diet. To simplify meal planning, portions of proteins, carbohydrates, and fats are divided into Zone Food Blocks. Instead of eating a certain number of calories, the dieter eats a specific number of Zone Blocks in the required proportions.
On the Zone diet, foods are either “good” or “bad.” Some “good” foods that are allowed (in the proper ratios) include:
Some “bad” foods that are restricted include:
Getting the protein :carbohydrate:fat proportions right requires a good bit of measuring and calculating, which can, at least at first, be time consuming and confusing. Zone participants are also instructed to do the following:
The science behind the Zone diet can be quite complicated and intimidating to someone not trained in biochemistry or nutrition. The explanation Sears gives of why the Zone diet works is based on an interplay of foods, the hormones insulin and glucagon, and hormone-like substances called eicosanoids.
The simplified explanation goes like this. When people eat, the level of glucose (sugar) in their blood increases. How much it increases depends on the foods they eat. “Good” foods with a low glycemic index (below 50) raise blood sugar less quickly than “bad” foods with a high glycemic index (above 65). When blood glucose levels increase, cells in the pancreas release the hormone insulin. This signals cells to convert glucose into a compound called glycogen that is stored in the liver and muscles and facilitates the storage of fat, stored in fat cells. When blood glucose levels go down, different cells in the pancreas release the hormone glucagon. Glucagon signals cells in the liver and muscle to release glycogen, which is converted back into glucose and is burned by the body. If glucose levels continue to be low, fat is also burned for energy.
According to Sears, carbohydrates, especially those with a high glycemic index (e.g. bread, cereal, sweets), cause the pancreas to release a lot of insulin, which in turn causes the body to store a lot of glycogen. Proteins, on the other hand, stimulate the body to release glucagon and burn stored glycogen, so that the body uses more calories.
Sears also says that another group of hormonelike compounds called eicosanoids comes into the food-insulin-glucose-glycogen equation. Eicosanoids are hormone-like substances that affect the immune system, nervous system, and cardiovascular system. “Good” eicosanoids reduce inflammation (irritation) in the walls of the blood vessels and help keep blood cells from clotting. This helps blood vessels stay open and prevents stroke and heart attack. “Bad” eicosanoids do the opposite. They cause inflammation and help blood to clot. Sears believes that increasing the amount of “good” eicosanoids to improve health can be done by following his diet. His books give a more complex explanation of the biochemistry involved in the process of regulating “good” and “bad” eicosanoids. Ultimately, he says that staying “in the Zone” by eating foods in the ideal proportions promotes both burning fat and cardiovascular health.
Barry Sears, developer of the Zone diet says that the makes the following claims for the Zone diet:
Many of these benefits are disputed by the dietitians and nutritional research scientists (see below). In addition, staying on the Zone diet while eating in restaurants can be quite difficult. Home delivery of perfectly balanced Zone diet meals and snacks is available at a price of about $37 per day in 2007.
People with reduced kidney function should discuss this diet with their doctor because of the high level of protein. Severely reducing the amount of grains eaten, especially whole grains, may lead to not getting enough dietary fiber. Dietary fiber plays an important role in maintaining bowel function. Too little fiber can result in constipation.
The core of the Zone diet is that everything a person eats should have a balance of 40% carbohydrates, 30% protein, and 30% fats. The 30% fats fits in well with what many dietitians and nutritionists recommend, and Sears emphasizes the use of olive oil and canola oil, both high in monounsaturated fats which are considered good for the body. However, 30% protein is considered high by many nutritionists and 40% carbohydrates is considered low. The federal health guidelines, Dietary Guidelines for Americans 2005, recommend consuming food in the proportions of 55% carbohydrates, 15% protein, and no more than 30% fats. These guidelines also recommend substantial consumption of whole grain products that are severely limited on the Zone diet.
In a review of the Zone diet published in Journal of the American College of Nutrition in 2003, the author questions the emphasis placed on the hormonal control of weight. He argues that although it is well documented that carbohydrates stimulate the production of insulin and proteins stimulate the production of glucagon, this occurs only when single nutrients are consumed. In a mixed meal consisting of protein, carbohydrates, and fats, such as those required by the Zone diet, the situation is much more complex and Sear's conclusions about hormonal response are simplistic. In the same article, the author questions the emphasis put on the role of controlling the production of eicosanoids through diet.
The claim that the Zone diet allows individuals to perform at peak physical performance is refuted by several studies by sports nutritionists who feel that limiting carbohydrates can harm athletic performance, especially among endurance athletes.
In an effort to determine which of several popular diets helped people keep weight off, researchers at Tufts-New England Medical Center in Boston assigned a group of volunteers to one of four diets: Atkins, Dean Ornish, Weight Watchers, and Zone diet. The found that regardless of the initial amount of weight lost, after one year, losses were only about 5% in all programs, meaning that these diets were all equally ineffective in helping most people keep weight off. These results were published in 2005 in the prestigious Journal of the American Medical Association.
In general, dietitians and nutritionists believe that any benefit from the Zone diet comes from the
reduction of calories and subsequent weight loss. They tend to feel that the same result can be achieved with a less complicated diet low in fats and high in fruits, vegetables, and whole-grain carbohydrates. They also question whether individuals on the Zone Diet get enough B-complex vitamins (found in large quantities in whole grains) without supplementation.
Sears, Barry. A Week in the Zone. New York: Regan Books, 2004.
Sears, Barry. What to Eat in The Zone: The Quick & Easy, Mix & Match Counter for Staying in The Zone. New York: Regan Books, 2004.
Sears, Barry and Lynn Sears. Zone Meals in Seconds: 150 Fast and Delicious Recipes for Breakfast, Lunch, and Dinner. New York: Regan Books, 2004
Cheuvront, Samuel N. “The Zone Diet Phenomenon: A Closer Look at the Science Behind the Claims.” Journal of the American College of Nutrition. 22, no. 9 (2003): 9-17 <http://www.jacn.org/cgi/content/full/22/1/9>
American Dietetic Association. 120 South Riverside Plaza, Suite 2000, Chicago, Illinois 60606-6995. Telephone: (800) 877-1600. Website: <http://www.eatright.org>
DrSears.Com Official Zone Web Page. Website: <http://www.drsears.com/>
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Harvard School of Public Health. “Interpreting News on Diet.” Harvard University, 2007. http://www.hsph.harvard.edu/nutritionsource/media.html>
Kellow, Juliette. “The Zone Diet Under the Spotlight.” Weight Loss Resources, March 16, 2007. <http://www.weightlossresources.co.uk/diet/zone.htm>
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“The Zone Diet.” Dietsfaq.com, undated, accessed April 17, 2007. <http://www.dietsfaq.com/thezone.html>
United States Department of Health and Human Services and the United States Department of Agriculture. “Dietary Guidelines for Americans 2005.” January 12, 2005. <http://www.healthierus.gov/dietaryguidelines>
Tish Davidson, A.M.