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Losing Propositions: A Discussion of Popular Diets
Dr. Saltzman is Assistant Professor of Medicine, Tufts University, and Director, Obesity Clinic, New England Medical Center. Ms. Rasmussen is Research Dietitian at Tufts.
RussellDiets come and go in popularity, but the ones that I hear the most about from patients are the Zone Diet, the Atkins Diet, the Pritikin Diet, the Ornish diet, and, lately, the "Blood Type" diet. How do these diets compare? Do they all recommend eating fewer calories and is that why they seem to work?
SaltzmanMost diets promise weight loss. There is only one way to lose weight by diet alone and that is by taking in fewer calories. So, when people lose weight on any of these diets, the reason is the same — because they are eating less. Some diets, however, make health claims. They promise to increase longevity, reverse atherosclerosis or help with other diseases or problems that have little to do with body weight.
Another thing that most of these diets have in common is that they go beyond calorie limits and target either specific macronutrients (e.g., fat, carbohydrate, protein) or particular types of foods. Most ask dieters to eat more, eat less or entirely avoid one kind of food or another.
For instance, the Zone Diet,(1) prescribes meals with very specific proportions of carbohydrates, protein and fat. Other diets are more general and rely instead on balancing the dieter's intake of different cateorgies of food over the course of a day.
RussellLet's start by discussing some of these diets in detail from the consumer's standpoint. Also,what dangers you feel may arise from following these diets on an everyday basis?
First, the Zone Diet. Can you give a general description of the Zone Diet and the theory that underlies it?
The Zone Diet
SaltzmanThe Zone Diet prescribes what it claims to be an ideal balance of food energy from carbohydrate, protein and fat. The "Zone balance" is 40% carbohydrate, 30% protein and 30% fat. The author of this diet, Dr. Barry Sears, stresses that its success depends upon eating that combination of macronutrients at each and every meal. Unfortunately, it can be difficult and inconvenient for consumers to cook meals that do this. Sears's answer to this problem is to offer for sale prepared food products that satisfy the Zone formula.
The Zone Diet is quite a change from the typical American diet, which generally has as much as 50-60% of energy from carbohydrate, and much less energy in the form of protein (more in the range of 15%).
The Zone Diet is based on combating insulin resistance and altering eicosanoid levels — what Barry Sears calls the "hormonal messengers" of the body. Eicosanoids are compounds produced by the body that influence many functions, including blood clotting, blood pressure and immunity. They are factors in both good health and disease. Sears suggests that a particular diet pattern can tilt the balance in favor of the beneficial or healthful eicosanoids. Similarly, Sears believes that a particular combination of dietary macronutrients can result in the best possible insulin:glucagon ratio. Insulin and glucagon are hormones secreted by the pancreas that work in opposition to regulate blood sugar levels. According to Sears, when these two hormones are in balance, body cells are better able to burn stored calories and prevent unwanted fat deposition.
To my knowledge, however, there are no data to back up the theory that either this particular combination of macronutrients, or the manipulation of hormonal influences, can deliver the benefits claimed.
RussellHelen, could you describe what this diet would actually look like at mealtime?
RasmussenThe Zone program is really quite complicated if you are doing it right. A typical breakfast might contain an egg-white omelet and lots of lower "glycemic" carbohydrates. Carbohydrates vary widely in how they affect blood sugar levels; those with a high glycemic index produce higher levels of sugar in the bloodstream than those with a low glycemic index. Examples of low glycemic carbohydrates are bulgur wheat and steel-cut "whole-oat" grains. These are not the types of grains found in bagels or other widely available breakfast foods. It can be quite laborious to plan and cook this sort of meal.
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