The Zone diet is an unproven dietary regime, which has been popularized by Dr. Barry Sears through sales of his 1995 book, The Zone. Despite claims made in the book, there is little available research to support its overall benefit.
The Zone diet is a calorie-restricted diet that provides adequate protein, moderate levels of carbohydrates, essential fats and micronutrients spread through three meals and two snacks that approximately maintain the protein-to-carbohydrate ratio throughout the day.
Proponents believe that the Zone diet promotes 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. Overall, the Zone's food plan consists of a dietary intake of 40% carbohydrates, 30% protein and 30% fat.
Under this diet, recommended foods include fruits and vegetables (fresh or frozen), oatmeal (whole grain), protein powder (e.g. soybean isolate), chicken, turkey, lean beef, fish, low-fat cottage cheese, soy food, nuts (e.g. almonds, cashews, macademia, pistachios), extra virgin olive oil, natural sweeteners, such as fructose or stevia.
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The Zone diet limits saturated fat and focuses on eating foods with "good" cholesterol, or HDL; promotes drinking at least eight glasses of water a day; encourages dieters to add some light exercise into the practice; promotes the eating of lean meats (like fish and poultry); promotes moderation; promotes the consumption of soy products, vegetables, fruit, and seafood, which are all considered to be beneficial foods; restricts carbohydrates, especially those with high-glycemic content.
Overall, the Zone diet is composed of approximately 30% fat, 30% protein, and 40% carbohydrates. The Recommended Daily Allowance (RDA) for protein is 0.80g/kg per day. Thus, for the 200lb (91kg) man, this equals 73g of protein daily. However, in the zone diet, 30% of the total calories are from protein, meaning that a 200lb man on a 1,400-calorie a day diet would consume 420 calories from protein each day. Since 1g of protein equals 4Kcal, 105g of protein would be consumed daily according to the Zone diet. This is 50% more than the RDA.
The Zone diet determines total daily caloric intake based on daily protein intake. Once the amount of daily protein is established, the next step is to divide this protein into 'blocks', each containing approximately 7g of protein. Divide up the consumption of these protein blocks into five or more meals throughout the day; for example: four at breakfast, three at lunch, two during afternoon snack, four at supper, and two at late night snack. Next, for each protein block an individual eats, one carbohydrate block and one fat block should also be consumed. Each carbohydrate block contains 9g of carbohydrate and each fat block has 1.5g of fat. The fat blocks are concentrated fat substances and this fat is in addition to fat that is contained with the protein and carbohydrate foods.
Suggested daily protein intake will vary based on daily activity and lean body mass. For the average overweight American, total caloric intake would be 1,400 calories per day. For an average marathon runner, the daily intake would be approximately 1,750 calories per day. Minimum daily protein recommendation is 75g for women and 100g for men.
The Zone diet recommends minimization of saturated fats (although many of the recipes included in this diet book would not be considered low in saturated fat) and stresses the intake of monounsaturated fats. Although this recommendation is similar to the Mediterranean diet, it is distinct in some regards. For instance, the Zone diet does not avoid creams and butter. The total intake of fat is recommended as 30% of calories and is generally consistent with an American Heart Association step 1 diet (10% saturated fat, 10% monounsaturated fat, 10% polyunsaturated fat). The fat intake recommended by the Zone diet may be seen as an improvement for the average American. However, for those already eating diets containing lower than 30% of calories from fat, it would not be advisable to increase fat intake as recommended by the Zone diet. In addition, people with heart disease or high cholesterol would require more aggressive fat restriction diets - for these people the unproven Zone diet would not be appropriate.
The types of protein consumed should be from low-fat sources. Carbohydrates should come primarily from foods with a low glycemic index. Generally, foods that are fiber-rich like fruits and vegetables have low glycemic indices while white bread, pasta, and potatoes are examples of foods with high indices that should be avoided. With regard to fat, saturated fats should be kept to a minimum. In place of saturated fats should be monounsaturated fats like olive and canola oil. Omega-3 oils like those contained in flax seeds and walnuts should also be minimized according to this diet.