The Zone Diet

Introduction

The Zone Diet was developed by Barry Sears, Ph.D., and popularized by Dr. Sears’ 1995 best-selling book, entitled, Enter the Zone. Although this diet is billed primarily as a weight-reduction diet, Dr. Sears believes the Zone Diet can prevent cancer, heart disease, and diabetes, and promote optimal physical and mental performance. The Zone Diet involves eating a specific percentage of calories from carbohydrates, proteins and fats (40%, 30%, and 30%, respectively) at each meal. This 40-30-30 diet prescription is believed to tightly control the body's production of insulin and glucagon, and powerful hormone-like substances called eicosanoids that control many vital physiological activities. Although the Zone Diet can be used successfully for weight loss, it restricts the consumption of carbohydrates and may lead to inadequate intake of fiber. In addition, because the total amount of food eaten per day is based only on an individual's protein requirements, the Zone Diet turns out to be a low-calorie diet that is not recommended for children, adolescents, and pregnant or lactating women as it may not meet their nutritional or caloric needs.

History

Dr. Sears began his work on the Zone Diet in the 1970s, shortly after his 53 year-old father died of a heart attack. At the time of his father’s unexpected death, Dr. Sears was studying the molecular structure of fats at the University of Virginia. Concerned that he, like his father, was destined for an early death, Dr. Sears altered the focus of his research and began to study the role of fats in the prevention and development of cardiovascular disease. During the next twenty years, Dr. Sears became convinced that heart disease can be prevented and that controlling the production of powerful hormone-like substances called eicosanoids is the key.

Popularity

The Zone Diet is popular among individuals desiring to lose weight, as well as athletes seeking to improve body composition and exercise performance. Reported sales for Enter the Zone exceed 3,000,000 copies, and the book has been translated into 16 languages. Dr. Sears has at least nine additional books related to the Zone Diet in print. In response to the popularity of this diet, hundreds of convenience foods that fit the Zone Diet's 40-30-30 recommendations have appeared on grocery store shelves. In addition, Zone Dieters can order “Zone Perfect” meals for home delivery on the Internet at www.zoneperfect.com.

Principles

The Zone Diet is based on a simplified interpretation of the complex relationships between two well-known hormones, insulin and glucagon, and a group of hormone-like substances called eicosanoids. Dr. Sears' rationale for his 40-30-30 diet prescription is presented below. Please see the Research section in this article for a critical review of this diet.

The story of the Zone Diet begins with insulin and glucagon, hormones that are secreted by the pancreas in response to the foods we eat. Although both hormones work to maintain blood sugar levels within a normal range, they have opposing actions. Insulin is a storage hormone. It facilitates the storage of blood sugar as glycogen in muscle and liver cells and/or as fat in fat cells, and is released when blood sugar levels are high. Glucagon, on the other hand, is a mobilization hormone. It stimulates the break down of stored energy and is released when blood sugar levels are low. According to Dr. Sears, the release of insulin is stimulated by the consumption of carbohydrates, while the release of glucagon is stimulated by the consumption of protein.

The next part of the Zone story is about eicosanoids. Eicosanoids are fats that contain 20 carbons. Included in the family of eicosanoids are prostaglandins, thromboxanes, and leukotrienes, all of which are hormone-like substances that control many vital physiological functions, including those of the cardiovascular system, the immune system, and the nervous system. Based on their physiological activity, Dr. Sears classifies some eicosanoids as “good,” and other eicosanoids as “bad”. For example, some eicosanoids have anti-inflammatory effects, while other eicosanoids prevent blood cells from clumping together. According to Dr. Sears, such eicosanoids are "good" because excessive inflammation and/or excessive clumping of blood cells is the cause of many degenerative diseases. On the other hand, "bad" eicosanoids promote inflammation or cause blood cells to clump together. In Dr. Sears' view, the secret to good health is to increase the body's production of “good” eicosanoids while decreasing the production of “bad” eicosanoids.

So what determines whether your body will produce "good" or "bad" eicosanoids?

According to Dr. Sears, the amount of protein and carbohydrate in the diet and the amount of insulin and glucagon in your blood are the determining factors. This will be explained in more detail later. But first, a brief explanation of how eicosanoids are produced:

The production of eicosanoids begins with two types of fat: omega-6 and omega-3 fatty acids:
The production of eicosanoids from omega-6 fatty acids begins with an omega-6 fat called linoleic acid (LA). In the process of making "good" eicosanoids, the body converts LA to gamma-linolenic acid(GLA) through a chemical reaction regulated by an enzyme called delta-6 desaturase. GLA is then converted to dihomogammalinolenic acid (DGLA), which is a direct precursor for "good" eicosanoids. Unfortunately, this fatty acid conversion story does not necessarily have a happy ending. DGLA can also be converted to compound called arachidonic acid by the enzyme delta-5 desaturase, and arachidonic acid is a precursor for "bad" eicosanoids.
The production of eicosanoids from omega-3 fatty acids begins with an essential fatty acid called alpha-linolenic acid. Alpha-linolenic acid is converted to eicosapentaenoic acid (EPA) through a series of reactions, one of which is regulated by delta-6 desaturase, and one of which is regulated by delta-5 desaturase. Although EPA is a precursor for "good" eicosanoids, Dr. Sears warns against eating foods that are rich in alpha-linolenic acid, such as flax seeds. This is because the enzyme delta-6 desaturase favors alpha-linolenic acid over linolenic acid, with the result that fewer omega-6 eicosanoids are produced.

As the explanation above suggests, the gatekeepers in the production of "good" and "bad" eicosanoids are the desaturase enzymes. Theoretically, high activity of delta-6 desaturase should result in production of "good" eicosanoids. However, the activity of this enzyme is slowed by several factors including age, viral infections, and, yes, diet! According to Dr. Sears, high carbohydrate, low protein diets are a recipe for disaster when it comes to “good” eicosanoid production. In his view, consumption of large amounts of carbohydrate decreases delta-6 desaturase activity thus lessening the conversion of LA to GLA. In addition, insulin (which is stimulated by carbohydrate consumption) increases the activity of delta-5-desaturase, further promoting the formation of arachidonic acid and "bad" eicosanoids. On the other hand, higher intake of protein increases the activity of delta-6 desaturase, thus increasing the conversion of LA to GLA, while glucagon (which is stimulated by protein consumption) decreases delta-5 desaturase activity, thereby reducing the formation of arachidonic acid and "bad" eicosanoids. In short, a diet that is high in protein and low in carbohydrate is ideal for producing "good" eicosanoids.

Originally, as part of his early work on the Zone Diet, Dr. Sears spent years researching the appropriate combination of protein and carbohydrate and decided that maintaining a healthy balance of eicosanoids required that each meal and snack contain a protein to carbohydrate ratio of 0.75, which translated into a caloric distribution of approximately 40% carbohydrate, 30% protein, and 30% fat. According to Dr. Sears, this ratio of macronutrients was viewed as the key to maximizing the activity of delta-6 desaturase and the production of “good” eicosanoids, and limiting the activity of delta-5 desaturase and the production of “bad” eicosanoids. In addition, according to Dr. Sears, people desiring to “live in the Zone” were best advised to avoid foods containing alpha-linolenic acid (for example, flaxseeds and pumpkin seeds) because alpha-linolenic acid was viewed as hampering the availability of delta-5 desaturase. Since the initial publication of Enter the Zone in 1995, Dr. Sears has published nearly a dozen new books related to the Zone Diet, including his 2003 publication The Omega Rx Zone. In this more recent publication, Dr. Sears reverses his earlier position on omega 3 fatty acids and actually recommends supplementation with omega-3 fatty acids. This change in Dr. Sears' position brings his recommendations much closer to the recommendations of other health experts to increase the consumption of omega 3 fats. See the Research section below for more information on the health benefits of omega-3 fats omega 3 fatty acids.

Unlike many weight loss diets, the Zone Diet does not intentionally restrict calories. Instead, the total amount of food eaten per day is based on the individual's protein requirements, determined by the dieter’s body weight, percentage of lean body mass, and level of physical activity. Once the daily protein requirement has been calculated, the dieter must divide the total amount of protein among three meals and two snacks and determine his/her allowable amount of carbohydrate intake, a task made easier by using Dr. Sears’ block concept. One protein block is equal to 7 grams of protein. If the daily protein requirement is 77 grams, then the dieter has 11 protein blocks to divide equally among meals and snacks. For every protein block allowed, the dieter must also eat a carbohydrate block, equal to 9 grams of carbohydrate. In addition, one fat block, representing 1.5-3 grams of fat, should be included with each meal and snack. Dr. Sears’ suggests that Zone dieters should never go more than five hours without a meal and should try to eat no more than 500 calories per meal or 100 calories per snack.

Research

According to Dr. Sears, the Zone Diet can prevent degenerative diseases by promoting the production of "good," or anti-inflammatory, eicosanoids. To support this theory, Dr. Sears draws on research that shows the effectiveness of supplementing the diet with essential fatty acids, including fish oil, evening primrose oil, and borage oil, in the treatment of various medical conditions, most notably cardiovascular disease and the autoimmune diseases (lupus, rheumatoid arthritis, and multiple sclerosis). By supplementing the diet with the proper amounts of healthy fats, eicosanoid production is manipulated, so that fewer inflammatory, and more anti-inflammatory, eicosanoids are made. As a result, patients experience a relief of symptoms and a regression of the disease process.

Additional support for the anti-aging benefits of the Zone Diet might be found in a growing body of research that links high levels of insulin (hyperinsulinemia) and a condition known as insulin resistance with the physiological changes that accompany aging. Abnormally high levels of insulin are associated with increased formation of free radicals, which are unstable oxygen compounds that have the ability to injure cell membranes, inactivate critical enzymes, and damage the genetic material in cells. Free radicals have been implicated in the development of many chronic and degenerative diseases, including cataracts, diabetes, cancer, and cardiovascular disease. Research indicates that a diet containing excessive amounts of carbohydrates and fat, in addition to lack of physical activity, may contribute to the development of hyperinsulinemia and insulin resistance. Although Dr. Sears believes that his diet prescription lowers insulin levels, he does not yet have any published clinical research to support this claim. As a result, the anti-aging claims of the Zone Diet may be premature.

Some research also supports the effectiveness of the Zone Diet in promoting weight loss. At least four clinical trials have evaluated the benefits of a reduced calorie, low-carbohydrate diet versus a reduced calorie, high-carbohydrate diet for weight loss. The results of these studies indicate that low-carbohydrate diets result in equivalent or greater weight loss than high-carbohydrate diets. Perhaps, more important than the amount of weight lost, however, is the finding in some studies that low-carbohydrate diets decrease insulin resistance. Decreasing insulin resistance can help promote weight loss by lowering insulin levels. Insulin participates in the storage of extra calories as fat, so by lowering circulating levels of insulin less fat is stored.

A primary criticism of the Zone Diet is that Dr. Sears’ overstates the impact that carbohydrates and protein have on insulin levels. It is true that carbohydrates, when eaten in the absence of fat and protein, produce a marked increase in the release of insulin. It is also true that, protein, when eaten in the absence of carbohydrates, causes an increase in glucagon levels with only a small increase in insulin. However, the Zone Diet is a mixed diet, meaning that carbohydrates, protein and fat are eaten simultaneously. As a result, it cannot be assumed that insulin levels will not increase, despite the high intake of protein and low intake of carbohydrate.

Furthermore, critics of the Zone Diet argue that Dr. Sears oversimplifies the research on the way in which protein, carbohydrate, insulin and glucagon impact the production of eicosanoids. For example, insulin is known to stimulate delta-6 desaturase activity and delta-5 desaturase activity, suggesting that insulin can promote the production of favorable eicosanoids as well as the production of unfavorable eicosanoids. Dr. Sears states only that insulin increases delta-5 desaturase activity. Also, carbohydrates have the ability to decrease delta-5 desaturase activity and delta-6 desaturase activity, indicating that carbohydrates can decrease the production of both bad and good eicosanoids. Dr. Sears states only that carbohydrates decrease the production of good eicosanoids.

Despite Dr. Sears purported success with highly-trained athletes, many exercise physiologists do not recommend the Zone Diet because it limits both carbohydrates and total calories. Glycogen, the form in which carbohydrate is stored in muscles, is the primary source of energy used to fuel exercising muscle. It is well-accepted that fatigue during exercise is caused primarily by depletion of glycogen stores. Most athletes’ glycogen stores are depleted within 90 minutes of intense exercise, leaving muscles without any quick source of energy to fuel activity. As a result, athletes who train daily require large amounts of carbohydrate (more than 500 grams per day) to perform at peak levels. In addition, endurance athletes have increased caloric needs, up to 5900 calories per day for men and 3100 calories per day for women. Because, on the Zone Diet, total caloric intake is determined by protein requirements, it is nearly impossible for athletes following this diet to take in a sufficient amount of calories. A small clinical trial that investigated the impact of the Zone Diet and a conventional diet (50-60% carbohydrate and 10-15% protein) on endurance capacity in highly trained triathletes found no benefit in following the Zone Diet's 40-30-30 recommendations.

Most nutrition experts concede that individuals who follow the Zone Diet carefully often experience significant weight loss. However, these experts point out that the Zone Diet is actually quite low in calories (1100-1700 calories per day), and that weight loss is a likely outcome of any diet that severely restricts calories. Critics also note that the initial weight lost on the Zone Diet is actually due to loss of water, not fat. Due to the restriction of carbohydrates, the Zone Diet depletes glycogen stores. Since glycogen is hydrated with 2-3 grams of water per gram, dieters experience rapid water loss.

Foods Emphasized

Individuals following the Zone Diet are encouraged to consume protein from animal and/or vegetable sources, and are especially encouraged to select protein foods that are relatively low in dietary fat such as chicken (white meat), soy foods, and legumes. The inclusion of monounsaturated fats including olive oil, canola oil, and avocados, is recommended. In addition, Dr. Sears recommends supplementing the diet with two fatty acids important for the production of "good" eicosanoids, GLA (gamma linolenic acid), which is found in oatmeal, evening primrose oil and borage oil, and eicosapentaenoic acid (EPA), which is found in fish. In his 2003 publication, , Dr. Sears also explores in some detail the beneficial role of omega 3 fatty acids when following a Zone Diet approach to food.

Foods Avoided

Individuals following the Zone Diet are encouraged to avoid:

  • All refined carbohydrates and most simple sugars, including foods made from white flour (bread, pasta, bagels, tortillas, and breakfast cereals), candy, soda, and desserts.
  • Fruits, vegetables and grains that are high on the glycemic index, such as rice, papaya, mango, corn, potatoes, and carrots.
  • Foods containing saturated fat, most notably red meat and whole-fat dairy products, should also be avoided.
  • Egg yolks and organ meats, due to their high content of arachidonic acid, a fatty acid that promotes the production of unfavorable eicosanoids.

Nutrient Excesses/
Deficiencies

Due to the restriction of carbohydrates, the Zone Diet may not provide a sufficient quantity of dietary fiber.

Who Benefits

Overweight individuals who have tried unsuccessfully to lose weight on low-fat diets may benefit from the Zone Diet.

Who is Harmed

The Zone Diet is a low-calorie diet and is, therefore, not recommended for any person with increased nutrient and/or caloric needs, including pregnant and lactating women, infants, children and adolescents.

Menu Ideas

The following menu ideas are taken from Enter the Zone by Dr. Barry Sears and are representative of the type and quantity of food included in the Zone Diet.

Breakfast

  • 1 1/3 cups cooked oatmeal with 1 cup low-fat cottage cheese

OR

  • 4 egg white omelet and 2 cups strawberries

Lunch

  • BLT Sandwich (1 slice whole-grain bread; 2 ounces extra-lean Canadian bacon, lettuce; tomato slice, dill pickle wedge; 1 ounce low-fat cheese)
  • 1/2 cupt plain low-fat yogurt with 1/3 cup canned peaches as dessert

OR

  • "Eggless" Egg Salad (9 ounces cooked, cooled, and mashed tofu with chopped scallions, parsley, paprika, and garlic salt; 4 teaspoons light mayonnaise)
  • 1 pita pocket with lettuce and tomato slice
  • 1/2 cup plain low-fat yogurt and 1 peach

Dinner

  • Curried Chicken (4 ounces sauteed chicken breast with chopped garlic, onions, and peppers; 1 tomato cut into wedges; 1 cup green beans)
  • 1 large tossed salad with 4 teaspoons olive oil and vinegar dressing
  • 1/2 cup grapes as dessert

OR

  • Tofu Stir-Fry (12 ounces tofu cut into cubes, with chopped onion, red and green peppers, mushrooms, and soy sauce; 2 1/2 cups chopped broccoli; 3/4 cup snow peas; 1 1/3 teaspoons peanut oil; 1/3 cup water)
  • 1 cup cubed cantaloupe as dessert

Resources

Barry Sears, Ph.D. has published several books related to "living in the Zone":
  • Enter the Zone
  • A Week in the Zone
  • Mastering the Zone
  • Zone-Perfect Meals in Minutes
  • Recipes from the Bestselling Author of the Zone and Mastering the Zone
  • Zone Food Blocks
  • The Soy Zone
  • The Anti-Aging Zone
  • The Age-Free Zone
  • The Top 100 Zone Foods

In addition, the official website of the Zone Diet, located at www.zoneperfect.com, provides information about the diet, an online calculator for determining protein needs, Zone recipes, and testimonials from Zone dieters.

Dr. Sears' web page, located at www.drsears.com, is also a great resource for people interested in learning more about the Zone Diet.

References

  • Anderson JW, et al. Health advantages and disadvantages of weight-reducing diets: a computer analysis and critical review. Journal of the American College of Nutrition 2000; 19(5): 578-590.
  • Brechtel L, Reer R, et al. High protein combined with low carbohdyrate intake does not enhance endurance. International Journal of Sports Medicine 1988; 19:S47.
  • Chevront SN. The Zone diet and athletic performance. Sports Medicine 1999; 27(4): 213-228.
  • Golay A, et al. Weight-loss with low or high carbohydrate diet. International Journal of Obesity 1996; 20:1067-1072.
  • Kelly G. Insulin resistance: lifestyle and nutritional interventions. Alternative Medicine Review 2000; 5(2):109-132.
  • Kerns, et al. Effects of two energy restricted diets on fuel utilization, blood chemistry and body composition. Medicine and Science in Sports and Exercises 1998; 30: S62.
  • Lemon PWR. Beyond the Zone: protein needs of active individuals. Journal of the American College of Nutrition 2000; 19(5): 513S-521S.
  • Piatti PM, et al. Hypocaloric high-protein diet improves glucose oxidation and spares lean body mass: comparison to hypocaloric high-carbohydrate diet. Metabolism 1994; 43(12): 1481-1887.
  • Preuss HG. Effects of glucose/insulin perturbations on aging and chronic disorders of aging: the evidence. Journal of the American College of Nutrition 1997; 16(5):397-403.
  • Sears B. . .
  • Skov AR, et al. Randomized trial on protein vs. carbohydrate in ad libitum fat reduced diet for the treatment of obesity. International Journal of Obesity 1999; 23:528-536.
  • Stein K. High-protein, low-carbohydrate diets: do they work. J Am Diet Assoc 2000 Jul;100(7):760-1.

This page was updated on: 2005-04-25 20:27:09
© 2002 The George Mateljan Foundation