Losing Propositions: A Discussion of Popular Diets

Diets 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?

Most 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, 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.

Let'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 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.

Helen, could you describe what this diet would actually look like at mealtime?

The 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.

What about eating the whole egg and what about typical American breakfast foods like fruit juices and coffee?

Actually, most fruit juices are not approved in the Zone Diet, an exception is grapefruit juice, which has a lower glycemic index. Instead, whole, raw fruits are recommended. The Zone Diet does not come down hard on eggs or other foods that are high in cholesterol. We have done some analysis in our lab of Zone diet meals and the saturated fat levels are actually quite high. These meals could contain up to 20-25% of total calories as saturated fat. As you know, the current recommended saturated fat intake is 8% or less of total calories. It is o.k. to drink coffee on this diet.

One of the more interesting parts of Dr. Sears' program is that he puts protein, fat and carbohydrate into blocks. According to Sears, people should eat certain protein blocks, carbohydrate blocks and fat blocks at each meal. He recommends that you eat these blocks about every 4.5 hours, which amounts to eating five times per day. It becomes almost a 24-hour job to remain in a "zone" state. Though somewhat ambiguous, the term "zone" apparently means keeping one's blood insulin levels at a low and consistent level. According to Sears, doing this will help suppress the appetite.

Lunch and dinner — even most of the snacks on the Sears diet — are similar to breakfast. Sears recommends raw vegetables, encourages fish intake for high eicosanoids and adds some whole grains, such as pumpernickel or wheat berry salad. Wheat berry salad is made by soaking the whole wheat grain in water so that it sprouts and plumps up to look like a berry. Rye berries are also recommended; like wheat berries, they have a low glycemic index.

Consumers trying to follow the Zone Diet can become quite exhausted from all the food preparation. They may be tempted to turn to the Zone direct-mail catalogue, which offers many frozen dinners as well as "40-30-30" bars, so you can always stay "in the Zone." These are expensive, as much as three or four times the price of brands such as Healthy Choice® or Budget Gourmet®.

Aside from weight loss, are there any other claims for the Zone Diet and are there any dangers from following this diet?

The Zone folks have recently claimed that following their diet can slow down the aging process. I am not acquainted with any research to substantiate this. It is unclear whether there are any ill effects from following this diet over the long term, largely because this diet is new enough that no one has followed it for very long. Theoretically, the consumption of higher amounts of protein than are currently considered healthy could result in accelerated bone loss and kidney damage. But again, there are no proven detrimental effects because we do not have long-term information on this diet.

Let us turn to the Atkins Diet. Ed, can you give a general description of that diet and the theory underlying it?