Response by Dr. Larry Weisenthal (runnswim@aol.com) to the following question posted on the bulletin board rec.sport.swimming, 15 May, 1996.

Can anyone send me, post, or refer me to articles or references that challenge the recent protein propaganda of Dr. Sears ("The Zone")?

O.K. As concise as I can make it:

Zone Claim # 1: The "Fattening of America" is related to an increased consumption of carbohydrate and a decreasing consumption of fat:

Fact #1: According to US government figures, total per capita fat consumption has actually increased, but sugar consumption has increased faster. Thus, Americans are consuming slightly more fat, vastly more sugar, more total calories, but a slightly reduced percentage of fat in the diet. As pointed out by Dr. Jay Kenney, this is equivalent to drinking whole milk alone or whole milk with several tablespoons of sugar. The latter may have a decreased percentage of calories as fat, but there is no reason to suppose that this would lead to weight loss, compared to drinking the whole milk alone.

Additionally, exercise has gone down and smoking cessation (which promotes weight gain) has gone up. 15% of adult Californians smoke today, compared to 60% two decades ago. Thus, the fattening of America is not owing to low fat/high carbohydrate diets.

Zone Claim # 2: Scientific studies conclusively show that high carbohydrate/low fat diets worsen blood lipids, raise blood pressure, and cause weight gain compared to lower carbohydrate/higher fat diets.

Fact #2: Every last one of these studies is fatally flawed, in that an isocaloric design was used. Subjects were forced to eat a set amount of food, the calories of which was the same in the high carbohydrate versus low carb arms of the study. They were also required to adjust caloric intake to maintain weight. The problem is that numerous studies have shown that when percent of fat in the diet is reduced, caloric intake is also spontaneously reduced. Put a person on a low fat diet, and that person will consume fewer calories and lose weight. Covertly adjust the fat content of the diet (make it equally palatable but just adjust the fat content covertly) and people eat more calories as the fat content is increased. Measure percent dietary fat as a function of body fat. The fatter people consume a greater percentage of their total calories as fat. And so on. Finally, ask the subjects in the isocaloric studies how they feel. The subjects in the low carbohydrate/high fat arm say that they feel fine. The subjects in the high carbohydrate/low fat arm say that they are being force fed, like a goose being fattened into foie gras.

In the real world, when you put people on high carbohydrate/low fat diets and they are allowed to eat what they want and are not forced to eat more, their blood lipids and blood pressure and blood sugar and serum insulin and body weight all improve. Published data confirm that they improve to a greater and more significant extent on the high carbohydrate/low fat diet than they do on the "Zone" Diet.

Zone Claim # 3: Up to 75% of the people in this country are "carbohydrate sensitive" and will be harmed by a high carbohydrate/low fat diet.

Fact #3: Fewer than 12% of people develop even a minor rise in serum triglycerides on a high carbohydrate/low fat diet. This rise tends to be minor and occurs even as the "big time" lipids (total cholesterol, LDLs) are getting better. And, with time, triglycerides tend to normalize or become reduced, compared with baseline levels, in the majority of this 12%. Also, triglyceride levels are very misleading for a number of reasons such as timing of the measurement (after eating vs. fasting) and types of triglycerides circulating ("fluffy/puffy" vs. "dense pack"), which I won't go into here.

Zone Claim #4: A high carbohydrate/low fat diet is harmful to your health. Eskimos prove that a very low carbohydrate diet can be healthful.

Fact #4: The longest-lived populations on Earth eat high carbohydrate/low fat diets. Vegetarians (80% carbohydrate/10% protein/10% fat) live longer than omnivores and have healthier, stronger bones. The longest-lived, healthiest industrial population (the Japanese) eat a high carbohydrate/low fat diet. Eskimos have a high incidence of cancer, tend to die young, and develop osteoporosis an average 10 years earlier than Canadians or Americans as a whole, despite a diet which is usually rich in both calcium and vitamin D.

Zone Claim #5: The Zone Diet is great for swimmers.

Fact #5: Swimming (workouts and competition) are largely anaerobic. Anaerobic metabolism is primarily carbohydrate. Swimming muscles use carbohydrate disproportionately to running or cycling muscles. Swimmers are much more carbohydrate depleted than are runners after workouts of comparable duration and intensity. Swimmers should consume a high carbohydrate/low fat snack immediately after a workout, to suppress an appetite for carbohydrate repletion which would otherwise cause the athlete to consume more calories, if the carbohydrate were to be repleted by food with a higher fat content. This may be one reason why it is harder to lose weight with swimming than with running. But weight control will be aided by suppressing appetite through the repletion of carbohydrate with pure carbohydrate, rather than with mixed carbohydrate/fat. A high carb snack post-workout will also help prevent muscle breakdown to liberate protein for conversion to glucose through gluconeogenesis to replete carbohydrate stores.

Even if you could train swimming muscles to "burn fat," this would be a disadvantage from the point of maximum performance. Aerobic carbo metabolism is faster (i.e. fuel can be provided faster to the exercising muscles) than is aerobic fat metabolism. Muscles fueled with carbohydrate perform better than muscles fueled with fat ("high octane" vs. "low octane" fuel). Aerobic fat metabolism consumes MORE OXYGEN per unit of ATP produced than does aerobic carbohydrate metabolism. Provided that fuel (carbohydrate or fat) is available, oxygen delivery and consumption are rate limiting. Because aerobic carbohydrate metabolism consumes less oxygen than aerobic fat metabolism, a carbohydrate burning muscle will perform at a higher level than a fat burning muscle.

Zone Claim #6: A high carbohydrate diet makes you sleepy because insulin secretion drives your blood sugar down and your glucose-starved brain goes to sleep.

Fact #6: A very large, high carbohydrate meal does make you sleepy, but it has nothing to do with glucose or insulin. High carbohydrate meal tend to promote a temporary alteration in serotonin levels in the brain, which make many people sleepy. This is probably why Italians take 2 hour lunches. Serotonin is a natural neurotransmitter and most experts agree that a post-noon nap is a natural thing, circadian-rhythm wise. There are practical ways to deal with the post-lunch yawns, however, which do not require the consumption of protein and fat. First, don't eat so much at one time (see below). Second, if you must gorge, follow it with a double espresso (as the Italians do). Third, go ahead and gorge and then just take a 10-15 minute nap when you get sleepy. This is a natural solution to a natural circadian rhythm phenomenon, which was figured out nicely by our ancestors, going back centuries.

Zone Claim #7: The only way to control an insulin system run amok is to eat food in 40/30/30 proportions.

Fact #7: If moderating insulin levels is one's goal (and it is really not all that important for the vast majority of normal people), this may be accomplished by (a) "nibbling" or "grazing," rather than gorging. This is actually recommended by Sears, himself. (b) eating preferentially carbohydrates of low caloric density, such as vegetables, rather than grains, and/or eating cooked grains (spaghetti, rice, cooked cereal), rather than dry grains of higher caloric density (licorice, Snack Wells, and, to a lesser extent, bread, crackers, and pretzels).

Zone Claim #8: The Zone Diet is good, because protein stimulates glucagon release, which does several good things for you.

Fact #8: If you take protein along with carbohydrate (as you always do on the 40/30/30 Zone diet plan), your glucagon levels don't go up. They only go up if you take in protein by itself, and this is only to compensate for the hypoglycemia which is produced when protein absorption stimulates insulin secretion (which it does) in the absence of dietary carbohydrate for the insulin to work on.

Zone Claims #s 9,10,11: The Zone Diet will prevent cancer, cure AIDS, help auto-immune disease, prevent Alzheimers, reverse heart disease, and make you live longer.

Facts #s 9,10,11: And I know of a nice bridge between Manhattan and Queens which is for sale, cheap.

Zone Claim # 12: The Zone Diet has favorable effects on eicosanoids (for those of you who care).

Fact #12: One important place where "good" eicosanoids play a role is in platelet aggregation. It is "bad" to have platelets which aggregate, since this can lead to heart attacks. Aspirin prevents heart attacks by inhibiting platelet aggregation, which is controlled by eicosanoids. Guess what. A high carbohydrate/low fat diet inhibits platelet aggregation, while a high monosaturated fat diet (advocated by Sears to improve eicosanoids) enhances platelet aggregation.

Zone Claim #13: Lowering your cholesterol doesn't lead to improvements in overall mortality.

Fact # 13: Yes, it does.

Zone Claim #14: Having a too-low cholesterol is dangerous to your health, leading to suicide, violence, cancer, and increased overall mortality.

Fact #14: No, it doesn't. [Although Dr. Weisenthal is unequivocal in this answer the research world is still debating this feature.]

Zone Claim #15: Dean Ornish's patients will have more heart disease and death, because they are not having all that much reduction in their coronary artery narrowing and their triglycerides are going up.

Fact #15: This is irresponsible scare mongering, which is likely to cause at least some heart patients to abandon their low fat diets, which will lead to some otherwise avoidable deaths. Coronary blood flow is proportional to the lumen diameter raised to the 4th power! Thus, even minor reductions will lead to major improvement in blood flow and heart muscle blood supply, as was clearly shown in a recent Ornish publication in JAMA. Also, his patients did NOT have significant elevations in triglyceride levels, which is, as noted above, not an important issue, for a variety of reasons.

Why I am so anti-Zone?

It's not that the diet is so gosh-awful horrible, it's that Sears is in the process of wrecking 25 years of slow, but steady improvements in public health awareness, without any foundation whatsoever in fact, for his own personal gain.

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