Dr. Saltzman is Assistant Professor of Medicine, Tufts University, and Director, Obesity Clinic, New England Medical Center. Ms. Rasmussen is Research Dietitian at Tufts.

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

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.

The Atkins Diet

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

The Atkins Diet is quite high in protein, very high in fat and very low in carbohydrate. The theory is that this pattern of consumption will bring down blood levels of insulin. This would, in turn, lead to decreased appetite, lower food consumption and weight loss. In its initial phase, the Atkins diet recommends that you take in as much as 50-55% of your total calories from fat, 30-40% from protein and somewhere in the neighborhood of 5-15% from carbohydrate. Meat, poultry, fish, dairy and oils are all permitted. Consumption of a diet with this particular balance would typically lead to a process called ketosis, which could both suppress appetite and lead to a sensation of well-being. This diet is recommended for weight loss only. To my knowledge, there are no other claims about anti-aging effects or combating disease.

Helen, what would this diet look like for breakfast, lunch and dinner to the consumer?

The most striking feature of this diet is its lack of carbohydrates. In fact, for what is called the "fortnight induction diet," or the initial phase of the program, dieters are limited to a total of 20 g/day of carbohydrates over a ten-day period, an extremely small amount. For breakfast, eggs, bacon and cream are all encouraged; Atkins warns consumers to go lightly on the milk because of its high carbohydrate content. A typical Atkins breakfast could be very high in saturated fat, but low in calcium and vitamin D. Lunch might consist of meats, poultry or fish, along with creamy sauces, and dinner would be the same. These are monotonous menus.

In trying to analyze the Atkins diet using the USDA Food Guide Pyramid, which represents the current conventional wisdom about proper nutrition, you would find most of the Atkins-recommended foods located at the top of the pyramid in the meat section or in the the "use sparingly" section of the pyramid. The Atkins diet is extremely unconventional, representing more or less an upside down version of the pyramid.

Ed, this doesn't sound like a healthy diet to follow long-term. Do we know anything about long-term results? And what is your feeling about how this diet would affect health and longevity, based on what we know about cardiovascular disease and cancer?

Again, we don't know much about the effects of following this diet over the long term. You would have to be concerned about vitamin and mineral deficiencies, since the diet is very low in fruits and vegetables. However, Atkins addresses this by recommending a number of supplements to along with the diet. These would, at least theoretically, prevent some of the deficiencies that might develop. I would note that Dr. Atkins promotes a particular brand of supplements.

As to long-term weight loss, it is hard to say at this point. However, I think it would be very difficult over the long term for anyone to restrict their carbohydrate intake to these low levels. It is also impractical, given the amount of eating we do outside the home and the amount of planning and preparation that this would require. There is also the question of whether such a high degree of fat intake might increase your risk for developing high blood fat levels, heart disease and certain types of cancers. In addition, since this diet is very low in fiber, approximately 5 g/day, constipation could well become an issue, as well as some of the chronic conditions that result from low fiber diets, including diverticulosis and colon cancer.

Yes, the Atkins diet contrasts quite markedly with the current recommendations for dietary fiber intake (between 20 and 30 g/day).

Let's turn, for a few minutes, to the popular Ornish and Pritikin diets. These two diet plans have more in common with one another than the other diets we have been talking about. Ed, could you describe these diets and the general theory that underlies them?

Ornish and Pritikin Diets

The theory underlying these diets is really the opposite of that of the Zone and Atkins diets. The Ornish diet calls for high levels of carbohydrates and low levels of fat, especially saturated fat. The Ornish diet originated as a way of combating atherosclerosis and even regressing coronary atherosclerosis. In the case of the Ornish diet, fat intake is limited to approximately 10% of total calories and protein to around 15% (which is the current average American intake). This means, of course, that the carbohydrate content is going to be quite high, as much as 75% of total calories.

Thankfully, the authors do not recommend consuming carbohydrates in the form of refined products but rather as whole grains, fruits and vegetables. It may well be that the reason why these diets are successful in causing weight loss is that their energy density (or the calories per gram or kilogram of food ingested) is going to be quite low, given all the fruits, vegetables and whole grains. Not surprisingly, fiber intake is also quite high.

The Pritikin program is similar to the Ornish diet. The Pritikin diet excludes processed grains, animal protein, eggs and fat.

This type of diet sounds healthy but it also sounds difficult to follow, particularly because of its low fat content. Could you outline what a typical dieter's meals would look like?

Dr. Ornish recommends eating a high level of carbohydrates and avoiding most animal products; what this amounts to is eating a lot of whole grain foods. He is not as concerned with differences in glycemic indices as are the other diet authors. He does give a list of ways that one can increase the carbohydrate content of our meals. For breakfast, for example, there would be certain whole grains (such as bulgur or whole grain pancakes), non-fat yogurt and fruit. As it eliminates most animal products, this diet contains very little cholesterol. Ornish also recommends using meat as a garnish rather than as a major protein component of lunch and dinner. He has developed many different recipes for stew-type meals, which have numerous ingredients. He encourages consumption of fresh vegetables and legumes. It can be quite laborious and time-consuming, however, to cook these foods.

Dr. Ornish recognizes that his diet is only one component in a plan for achieving cardiovascular health. His "Open Your Heart" program recommends that people get together to create a "mindfulness," or communication and spiritual connectedness with others. He conducts group therapy sessions and encourages physical exercise as well as deep relaxation techniques. He discourages alcohol intake, but does not absolutely prohibit it.

Ed, this sounds like a diet that might induce hyperinsulinemia, or elevated levels of insulin in the blood, which, theoretically, would be a bad thing. It is also, in fact, what the Zone Diet and Atkins Diet are intended to prevent. Haven't studies shown a link between hyperinsulinemia and certain diseases?

I think it is important to remember that the link between hyperinsulinemia and chronic disease has been identified mainly at epidemiologic (statistic) levels. It is unclear whether for a particular individual, hyperinsulinemia really leads to any increased risk of disease. Based on the epidemiological research, you might expect that people consuming a high carbohydrate diet would have problems with blood pressure, atherosclerosis or other chronic diseases. Yet it appears that people consuming diets like the Ornish program are able both to lose weight and to improve their cardiovascular health. I suspect that the relationship between carbohydrate intake, insulin levels and overall health may be very complex.

For one thing, our food choices affect the level of insulin in our blood in many ways. Consumption of whole grains, fruits and vegetables, especially foods with soluble fiber, is going to lessen the effect of the dramatic rise in insulin levels that normally occurs in our bloodstream after mealtimes. Thus, people following this diet may actually not have as high levels of insulin after eating as people on lower carbohydrate diets, but this depends as well upon the type of carbohydrate and other variables.

There does not seem to be any theoretical risk of following this diet over the long term, and I gather that there is some evidence that well motivated people have followed this diet successfully for long periods.

Another new diet is known as the "Eat Right for Your Type" (as in "blood type"). Helen, could you describe this diet?

The "Eat Right for Your Type" Diet

This diet premise is based on what Dr. Peter D'Adamo, who is a naturopathic physician, thinks are "evolutionarily appropriate" diets for people with different blood types. Briefly, he believes that someone with an "O" blood type (as found in the oldest evolutionary animals) should not consume wheat or carbohydrate foods, but rather should consume a very high protein, high fat diet. From what we know, this is not a healthy diet if followed for a long time, and is very similar to the Atkins diet.

Those with the "A" type (the next blood type to evolve) should eat a lot of carbohydrates. Then, there are the "B" and "AB" types who, supposedly, have developed more recently, so they actually have a more "adaptive" intestinal capability. "B" and "AB" people can eat a varied diet, particularly including dairy foods.

To follow the "Type" diet, you need to know your blood type in order to figure out what foods you can eat. There is no scientific evidence that this makes sense. In my opinion, this is less a sensible diet than a parlor game.

Our Recommendations

Ed, you are a physician who takes care of patients with obesity and people who are trying to lose weight. What dietary advice do you give your patients? Have you ever recommended any of these diets?

In helping people to lose weight, I try to identify the aspects of their diet lifestyle that can be modified. For a number of individuals, the main problem is that they consume excess calories from foods that have no great nutritional value, such as sweets or high-fat foods. As a rule, I do not recommend any particular balance of macronutrients for patients, although I do believe that a diet rich in fruits and vegetables and whole grains does promote weight loss, possibly in part by decreasing energy density or increasing volume. In general, I believe in looking at individual factors, such as dietary proteins and whether the individual has a trigger food that stimulates consumption of more and more calories. For some individuals, it is carbohydrates. For these people I recommend a reduction in some types of carbohydrates, but I never recommend the kind of severe limitations that are found in the Atkins plan.

Helen, what do you recommend for people trying to lose weight?

Food Guide Pyramid Diet

The diets that work the best for the people who have talked to me are pretty simple. People eat their favorite foods but learn to control portion sizes and eat more sensibly. Many have used guides such as the Food Pyramid and initiatives like Five-A-Day, which give them simple nutritional messages on how to incorporate, for example, more fruits and vegetables into their diet.

I think weight loss cannot be successful unless it is accompanied by a program of physical activity. You have to get off the couch, get away from the computer and get some physical exercise. If you do go on a weight loss program, it is a good idea to run it by your health care practitioner to make sure you are getting enough vitamins and minerals. For most people, anything less than about 1500 calories a day could result in micronutrient (vitamins and minerals) or calcium deficiencies. In that case, some kind of multivitamin or multimineral supplement might be needed.

Adequate hydration and dietary fiber are also key to any weight loss program. A person needs about 20-25 g of fiber/day. If one wanted to follow the Food Guide Pyramid for weight loss, the number of servings should be:six servings of the bread group, four to five of vegetables, two of fruit and five ounces of meat. This is, approximately, 1600 calories. The Food Guide Pyramid recommends about 30% of calories from fat, 15% from protein and 60-65% from carbohydrates. Table 1 compares and contrasts the various diets. To help in using the Food Guide Pyramid, teaching sheets are available. In addition to the 1600-calorie diet plan, there are sheets for 2000 calories and 2400 calories (Table 2). These can be used for weight loss diets which do not drastically alter a person's food choices.

Table 1.
Comparison of Selected Popular Diets.
Diet Diet Composition* Foods Specified Diet Claim Proposed Mechanism
Dr. Barry Sears' Zone Sears' Diet 40% carbohydrate, 30% protein, 30% fat. Calories are restricted. 3 meals, 2 snacks/day
<400 kcal/meal
Low GI* foods
Eating the "right food" leads to a metabolic state whereby the body has increased energy, decreased hunger. Lower insulin levels, optimal eicosanoid levels are the "master switches" for decreased hunger.
Dr. Atkins' Weight Loss Diet "Fortnight Diet": 36% Pro, 8% CHO, 53% fat. Maintenance: 24% protein, 40% fat, 31% carbohydrate. No calorie restriction. Meats, cheese, eggs, poultry, fats and oils required. Grains, fruits and vegetables severely restricted. Eating too many carbohydrates cause obesity. High protein, high fat leads to decreased hunger. A ketogenic diet causes incomplete oxidation of fatty acids by the liver, resulting in ketone bodies in blood and urine.
Dr. Dean Ornish's Reversing Heart Disease Program <10% fat, 15-20% Pro, 70-75% CHO
5 mg cholesterol/day
No calorie restriction
Recommends whole grains, fruits and vegetables, and very little meat, dairy or fat. Lowering fat lowers blood cholesterol, which forms plaque and tears the lining of coronary arteries. Reduces plasma cholesterol, LDL cholesterol. Documented atherosclerotic regression.
Pritikin Diet 8-12% Fat, 12-15% Pro, 80% CHO. <100 mg cholesterol/day. Recommends whole grains, fruits and vegetables, minimal fat and animal products. Low fat diet increases energy. Low fat diets reduce plasma cholesterol, LDL ("bad") cholesterol. Low oxygenated blood is increased in a high fat diet, causing clogged arteries, capillaries, etc. Low fat diets will carry more oxygen to cells.
Food Guide Pyramid Diet <30% fat, 55-60% carboydrate, 10-15% protein. Also defined as a diet that is adequate in vitamins, minerals and dietary fiber w/out excessive amounts of calories, fat, sat. fat, cholesterol, sodium, added sugars, alcohol. Specifies servings of food groups:
  • Grains, breads, etc:6-11 svgs.
  • Fruits:2-4 svgs.
  • Vegetables:3-5 svgs.
  • Meat,eggs,nuts, dry beans, poultry, fish: 2-3 svgs.
  • Dairy: 2 svgs.
  • Fats,sweets, alcohol: use sparingly & moderation.
Diet was created to help healthy Americans follow the Dietary Guidelines for Americans:
  • Variety
  • Choose plenty of grains, fruits & veg
  • Keep diet low in sat. fat and cholesterol
  • Keep diet moderate in sugars, salt and sodium
  • Moderate alcohol
  • Physical activity and maintain or improve your weight.
This diet was designed to address nutrient adequacy and nutrient excess in a healthy population. If followed over a period of time (i.e., a week at least), this diet allows food choice flexibility and a practical balance in levels of calories, fat and sodium. Certain populations consuming lower calories (than 1600) may not meet the full RDA for certain nutrients.
*CHO=carbohydrate, Pro=protein, GI=glycemic index

Table 2.
One Day's Menu and Food Group Servings at Three Calorie Levels
Item Calorie Level
  1,600 2,200 2,800
Cantaloupe 1/4 medium 1/4 medium 1/4 medium
Whole-wheat pancakes 2 2 3
Blueberry sauce 1/4 cup 1/4 cup 6 tablespoons
Margarine   1 teaspoon 2 teaspoons
Turkey patty   1 1/2 ounces 1 1/2 ounces
Milk skim, 1 cup skim, 1 cup 2%, 1 cup
Chili-stuffed baked potato 3/4 cup chili, 1 potato 3/4 cup chili, 1 potato 3/4 cup chili, 1 potato
Lowfat, low-sodium cheddar cheese   3 tablespoons 3 tablespoons
Spinach-orange salad 1 cup 1 cup 1 cup
Wheat crackers 6 6 6
Grapes     12
Fig bars     2
Milk   skim, 1 cup 2%, 1 cup
Apricot-glazed chicken 1 breast half 1 breast half 1 breast half
Rice-pasta pilaf 3/4 cup 3/4 cup 3/4 cup
Steamed zucchini     1/2 cup
Tossed salad 1 cup 1 cup 1 cup
Reduced-calorie Italian dressing 1 tablespoon 1 tablespoon  
Regular Italian dressing     1 tablespoon
Hard rolls(s) 1 small 2 small 2 small
Margarine   2 teaspoons 2 teaspoons
Vanilla ice milk 1/2 cup 1/2 cup 1/2 cup
Fig bar 1    
Skim milk 3/4 cup    
Apple   1/2 medium 1/2 medium
Soft pretzel   1 large 1 large
Lemonade     1 cup
2% fat milk     1 cup
Number of Servings
Bread group 6 9 11
Vegetable group 4 1/4 4 1/4 5 1/4
Fruit group 2 1/3 2 3/4 4
Milk group 2 2 2/3 3 2/3
Meat group (ounces) 5 1/2 7 7
Nutrient Data
Calories 1,665 2,199 2,859
Fat1, g 38 59 87
Percent calories from fat 20% 24% 27%
Saturated fat1, g 11 17 27
Percent calories from saturated fat 6% 7% 8%
Cholesterol, mg 183 236 309
Sodium, mg 1,861 3,138 3,508
Dietary fiber, g 23 25 31
1Values have been rounded to the nearest whole number.
Source: Using the Food Guide Pyramid: A Resource for Nutrition Educators. USDA Food, Nutrition and Consumer Services, Center for Nutrition Policy and Promotion.