Scientific Analysis of The Zone Dietby Jan McBride, M.D.
Zone dieting is designed to avoid ketosis, which the author claims causes one to lose muscle mass even with high protein diets. He also claims that high levels of protein in a meal cause high insulin levels, which converts the protein into fat. The concept of "the Zone" is that food should be treated like a prescription drug that is designed to promote the desired hormonal response throughout the day. The hormones in question are insulin, glucagon, and eicosanoids. Insulin and glucagon are well known hormones, and their functions are described accurately. The author describes eicosanoids as, "the most powerful biological agents known to man", yet admits that they are all but unknown, even to the medical community. The goal of Zone dieting is to eat the correct balance of carbohydrates and protein so that glucagon is produced instead of insulin, because glucagon promotes the formation of "good" eicosanoids while insulin promotes the formation of "bad" eicosanoids that cause all sorts of diseases. To reach the Zone, one must consume foods in a protein-to-carbohydrate ratio of 0.75, which is 3 grams of protein for every 4 grams of carbohydrate, at every meal and snack, and without allowing more than 5 hours between meals or snacks. The author converts grams into blocks of protein and carbohydrate and provides food lists and meal plans for these. He distinguishes between carbohydrates with high versus low glycemic indexes, which is a measure of how fast the carbohydrate is digested for each food type. In addition, he adds fat "blocks" to his meal plans and distinguishes between various types of fats, recommending against saturated fats and favoring monounsaturated fats, due to their effect on eicosanoid production. Protein requirements in the Zone are based on lean body mass and level of physical activity (the same method that is used in Protein Power). The lean body mass is calculated using standardized charts that use height, hip and abdomen measurements in women and weight, wrist and waist measurements in men. The calculated protein requirement is not to be exceeded, and is to be spread throughout the day, to avoid increased insulin levels caused by protein digestion. Therefore, a person would end up with a calorie limit on their total daily intake, since protein has a maximum value, and carbohydrate and fat intake are measured by protein intake. The second half of the book is a description of how Zone dieting can improve numerous health conditions, primarily based on the eicosanoid activities.
In this book the author provides excellent scientific explanations for how too many carbohydrates in the diet cause fat storage. The entire design of the Zone diet is also explained in a very scientific fashion, however, it is greatly lacking in scientific evidence to support it. The concept is correct that providing higher levels of carbohydrates would avoid ketosis, which is a condition that may be hazardous over the long term, however, because of a restriction on the intake of protein, carbohydrate and fat, it is likely that insufficient calories and carbohydrates will be available for most people to avoid ketosis. In other words, the ketosis that results from starvation - getting too few calories to meet basic needs - can easily occur in many persons based on their Zone calculations for daily intakes. There may also not be enough protein in the diet to prevent loss of muscle mass. In my research on protein requirements, I did not find any valid evidence for using activity level as a basis for protein intake. In the absence of glucose the muscles use fat for energy, and do not need more or less protein for activity. When protein is "broken down" to provide fuel, the actual molecules are conserved while the bonds between them are broken. To restore the protein molecules only energy is required to reform the chemical bonds. This is in opposition to the author's statement that, "the higher your physical activity level, the faster the rate that you're breaking down protein. As a result, you'll need to increase your dietary protein intake to repair and rebuild muscle that gets damaged during higher levels of physical activity". An additional consideration is that a person's protein requirements depend on what other nutrients are consumed as energy sources. When carbohydrates are restricted in the diet, more protein is needed to be converted to glucose as fuel for the brain. If this author would increase the protein requirement in consideration of this, and also allow for consumption of protein above the minimum level, then I would be concerned that the ratio of carbohydrate to protein would be too high for many persons to avoid excess insulin production. The author's concern that excess protein in any meal can cause excess insulin and cause the protein to be stored as fat is without scientific evidence. True, the protein can be converted to glucose, which in turn can be converted to glycogen in the liver and to fat in other cells, but energy input is required for these processes, and the body has mechanisms to avoid spending energy on creating substances in excess of its needs. For the most part, excess protein is disposed of, glucose is stored as glycogen, and fat is stored as fat. There are so many scientific errors in the Zone that it is becomes very complicated to describe them all - but then again the Zone formula is extremely complicated. Let's try to simplify it. 1) Scientific
evidence shows that the total amount of protein should not be restricted,
which the Zone does. Here are some examples to illustrate: A 150 pound woman who is sedentary and overweight calculates her body fat at 33%. Her Zone protein requirement comes out to 60 grams. Her Zone carbohydrate portion is 80 grams daily, which may be too low to inhibit ketosis. Her fat portion is 13 grams. Her total daily calorie intake is 677 calories, which is extremely low. If we even consider that her protein foods will include about 1/3 fat and add another 180 calories, she is still getting only 857 calories daily. Not only will she have to be in ketosis to supply her baseline energy needs, she will also lose muscle mass due to low protein intake. Compare to this a 150 pound world-class athlete who has 21% body fat and is extremely active. Even though her weight is the same, her body fat and activity level give her a protein portion of 186 grams daily, 3 times that of the sedentary woman! She also will get 153 grams of carbohydrate, which she will probably "burn" as fuel, and 26 grams of fat. With an additional 1/3 of her protein foods considered as fat, she gets 1682 calories daily. On days she is extremely active, she probably will experience ketosis for many hours of the day despite the high protein intake, because her total calories are restricted. She may even lose muscle mass since her intake of fat for fuel is restricted. On days when she is less active, she will probably have to dispose of a large portion of her protein, and will experience moderate insulin levels due to the high carbohydrate intake. It is easy to see why the Zone diet has worked in athletes, because they are probably getting close to their protein and energy needs. I can only guess that the popularity of the Zone diet is due to persons using the recommended ratios but not limiting their intake to the calculated portions of carbohydrate, protein and fat. The author indicates that he has tested this diet on numerous persons, and found that the better you play the "eicosanoid game" the better your results. The only data he provides, however, is body fat changes and athletic achievements by specific athletes and teams. There is no way to tell whether these results are due to his protein/carbohydrate ratio, or merely to decreased carbohydrate intake. And I must question, how do you know what your "results" are, or whether you are "in the Zone"? One issue not brought up by the Zone diet is that of cholesterol levels. All of the low carb diet plans should improve cholesterol levels, except possibly for this one. Scientific evidence shows us why consuming fewer carbohydrates should cause LDL or "bad" cholesterol to decrease. In the Zone the level of carbohydrates consumed may not be low enough to achieve this, especially for someone who has a large lean body mass and, therefore, a high calculated carbohydrate intake. Additionally, fat in the diet has been shown to increase HDL or "good" cholesterol, and saturated fat promotes the greatest increase. The Zone diet not only limits fat intake, but also advises against the use of saturated fat. As for eicosanoids, I could not find any general articles about these substances, but am familiar with the specific ones mentioned, and can accept on a scientific level that this author has gleaned details from unrelated studies and put them together to form the picture of eicosanoids he presents. Whether or not the control of eicosanoid production by specific nutrient intake provides all the effects he claims is not at all scientifically proven. At any rate, what he does not tell you is that you can get the same production of "good" eicosanoids by merely limiting carbohydrate, as all of the low carb diets do, because they promote the release of glucagon rather than insulin. In fact, if the protein intake were unlimited, as it should be, using the Zone ratio of carbohydrate to protein at each meal would probably stimulate insulin and "bad" eicosanoids in most persons. Lastly, I believe the Zone diet is extremely too complex for most persons to follow with any consistency - and unnecessarily so. I do not believe that the human body is so fragile that one must think of food as a prescription drug, and eat in specific ratios at each and every meal. The production of ketones is natural for the body, and occurs between meals and overnight with any diet as fat is used for energy. Although it is advisable to avoid ongoing higher levels of ketosis for long periods of time, it is not necessary to try to keep it from ever happening by eating in such a restricted pattern. The Zone may actually provide some persons with the ideal amounts of protein, carbohydrate and fat, but how would they know? What parameter can they monitor to know if they are obtaining the correct results? My recommendation for anyone on this diet is to have lipid profiles tested, to see if cholesterol levels are in desired ranges. If they are not, then the Zone you are in is not the correct one for you. "DIET TRUTHS REVEALED: The IDEAL DIET for Human Health" presents a version of the low carb diet that is healthy for long-term use, whether you need to lose weight or not. It also recognizes that one diet does not fit all persons, and provides guidance on adapting the low carb diet to your lifestyle and metabolic needs. Persons who have a slow metabolism may find it difficult to lose weight even with a low carb diet. For these people, the "Metabolic Switch" diet can provide success. This method is described in DIET TRUTHS REVEALED. Food lists, sample menus and charts are provided to guide you in starting, adapting and continuing the diet for your long term weight maintenance and good health. You can order DIET TRUTHS REVEALED by mail for only $14.95 plus $5.00 shipping and handling, or by instant download.
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