The Zone (40:30:30) Diets
The Zone diets state that your meals should be built around protein. The ideal numbers (according to these diets) are: Protein should represent (by calories) 30% of your meal, Carbohydrates 40% and Fat 30%. When your meals equal those numbers you're, "in the Zone."
Fiber-rich vegetables and fruits. You should eat protein with every meal and snack. The carbohydrates you eat should be twice the size of the protein portions.
Good foods would include beans, lentils, most fruits, vegetables and whole-grains.
Bad foods (or "unfavorable carbohydrates") include brown rice, bagels, bananas, fruit juices and pasta. If you must eat these foods it should be in smaller portions.
How it Works
The Zone diets claim weight loss is achieved through the regulation of fat storing insulin and hormone glucagons. Insulin is a hormone that the body uses to help regulate storage of excess energy as fat. Glucagon is responsible for releasing stored glucose from the liver when it is needed. By balancing the amount of each of these hormones through what you eat you will loose weight.
The reality is the Zone diet is essentially a restricted calorie diet. The average person (according to Dr. Barry Sears) should consume between 0.8 and 1.0 grams of protein per pound of lean body mass. Following the Zone diet recommendations a 150 lb man eating the ideal combination of 40% carbohydrates, 30% proteins and 30% fat should consume approximately 1184 calories daily. That's 800 calories less than the average set by the United States Department of Agriculture (USDA). Cut your caloric intake almost in half and of course you're going to loose weight.
Pros and Cons
The root of the Zone diet is the concept that obesity and poor health are the result of carbohydrate intake and the insulin used to process sugars. Dr. Sears maintains that if you eat the wrong foods your body produces more insulin and the increased insulin results in obesity. Just change your diet and you will lower your insulin and loose weight.
While it is true that obese people often have higher levels of insulin, the reason they do is because excess body fat tends to make the individual less sensitive to insulin's effects, and as a result more insulin must be manufactured to maintain a steady blood sugar. High insulin levels do not result in obesity; obesity leads to higher insulin levels. When a person loses weight their body no longer requires as much insulin and so generally the insulin levels decrease.
Another premise of the Zone is that insulin and glucagons regulate eicosanoid production. Eicosanoids are hormone-like compounds which include prostaglandins thromboxanes and leukotrienes. Dr. Sears suggests that there are good and bad eicosanoids and that by regulating them you can loose weight. Unfortunately there is no scientific evidence that shows any diet can control eicosanoid production via insulin and glucagons.
The Zone diet may also hinder athletes. The recommendations for caloric and carbohydrate intakes are not sufficient to meet the energy requirements of a regular training program.
The Bottom Line
The Zone diets' recommendations of a diet comprised of 30% proteins, 40% carbohydrates and 30% fats does not stand up to scientific scrutiny. Ultimately persons who strictly follow the Zone diet will loose weight because they are consuming fewer calories rather than any changes in insulin, glucagons or eicosanoid production. Until studies have been performed to validate Dr. Sears claims we cannot recommend this diet plan.
As with any diet what these books suggest should NEVER be attempted without the supervision of a Medical Doctor or licensed Nutritionist.
General Reference Links
American Heart Association
Center for Science in the Public Interest
Centers for Disease Control and Prevention
National Institutes of Health
United States Department of Agriculture