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 PhD. 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 best seller. Since then he has written a dozen books and cookbooks about the Zone diet, established a website, and developed a program of home-delivered Zone meals, turning the Zone diet concept into a multimillion dollar business.
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.
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 hormone-like 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, makes the following claims for the Zone diet:
Many of these benefits are disputed by the dietitians and nutritional research scientists. 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.
This diet is unlikely to meet the calorie and nutritional needs of children, pregnant women, or breastfeeding women, even though Sears suggests that pregnant and breastfeeding women increase their food intake by about 25%. In addition, Sears recommends that people on the Zone diet take dietary supplements. He specifically mentions calcium and omega-3 fatty acid supplementation. Other supplements may also be necessary.
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 registered dietitians 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 registered dietitians, and 40% carbohydrates is considered low. The federal health guidelines, Dietary Guidelines for Americans, 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. The researchers 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, most registered dietitians 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.
See also Anti-aging diet ; Anti-inflammatory diets ; Glycemic index diets ; High-protein diet .
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. Rev. ed. 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. 1 (2003): 9–17.
Dr. Sears official website. http://www.drsears.com (accessed April 23, 2018).
Kellow, Juliette. “The Zone Diet Under the Spotlight.” http://www.weightlossresources.co.uk/diet/zone.htm (accessed April 23, 2018).
U.S. Department of Health and Human Services and U.S. Department of Agriculture. 2015–2020 Dietary Guidelines for Americans. 8th ed. December 2015. http://health.gov/dietaryguidelines/2015/guidelines/ (accessed May 1, 2018).
“Zone Diet.” U.S. News & World Report: Health. http://health.usnews.com/best-diet/zone-diet (accessed May 1, 2018).
Tish Davidson, AM