Defending "The Zone": where's the evidence? - examining the pros and cons of the low-carbohydrate diet

I find it unfortunate that your readers were subjected to a great number of scientific inaccuracies. It is obvious that Ms. Liebman misunderstood the entire point of my book, The Zone, which is that the key to health is maintaining insulin within a relatively narrow zone: not too high, not too low....Nonetheless, let me comment on each of Ms. Liebman's critiques of my statements.

Claim #1: Americans are fatter because we eat less fat.

Ms. Liebman forgot to [add] "and more carbohydrate"....

Even using her contention that fat consumption has not changed, it is clear that the total increase in calories (100-300 per day) is coming purely from carbohydrates. The central theme of The Zone is that excessive consumption of carbohydrates causes an increase in insulin, which in turn increases fat accumulation....

Ms. Liebman simply forgets that the best way to fatten cattle is to feed them excessive amounts of low-fat grain. Likewise the best way to fatten humans is to feed them excessive amounts of low-fat grain, but now in the form of bagels and pasta.

Claim #2: Carbohydrates cause obesity.

Again Ms. Liebman has missed the central focus of The Zone, which is insulin control. It is excess insulin that makes you fat....

There are two dietary methods to increase insulin. One is to eat too many carbohydrates, and the other is to eat too many calories containing protein and carbohydrates (fat has no effect on insulin). When you do both, as do most Americans, you have a sure-fire prescription for fat accumulation.

Ms. Liebman quotes Dr. Gerald Reaven, who states that "a calorie is a calorie is a calorie." I agree. Unfortunately, the hormonal effect of a calorie of carbohydrate is different than the hormonal effect of a calorie of protein or fat....

Then she quotes a study done by Dr. Reaven which shows that two different 1,000 per day calorie diets produced the same fat loss in metabolic ward patients.(1) What she failed to tell the readers is that one diet was... 15% carbohydrate and 53% fat and the other was basically a Zone diet (45% carbohydrate, 26% fat, 29% protein). In both diets, insulin levels were lowered. It is only when you lower insulin levels that you can access stored body fat....

If Ms. Liebman had made a careful survey of the literature she would have found a classic study published in Lancet nearly 40 years ago that compared weight loss in overweight individuals on different 1,000 calorie per day diets under hospital ward conditions. On diets composed of 90% of calories as fat, the patients lost approximately one pound of weight per day. On 90% protein, the patients lost approximately 0.6 pounds of weight per day. Obviously, neither of these diets is realistic. Using a mixed diet with 42% of the calories as carbohydrates (basically the Zone diet), the patients lost approximately 0.4 pounds per day. And what about a 1,000 calorie per day diet consisting of 90% carbohydrates? The patients actually gained weight(2)....

Claim #3: Calories don't count... protein does.

....Protein does count....The Zone diet is based upon a protein-adequate diet individualized to a person's unique needs. Simply stated: one size does not fit all. Once an individual's daily protein intake that maintains his or her lean body mass is calculated, that amount of protein is then spread throughout the day in three meals and two snacks. The amount of protein at each meal or snack dictates how much carbohydrate and fat should be consumed at the same time to maintain insulin in a relatively tight zone; not too high [or] low....

It is also difficult for me to understand Ms. Liebman's statement that no evidence exists "that eating equal amounts of protein and carbohydrate at every meal lowers insulin levels" when she quoted a study by Reaven that shows that the protein-to-carbohydrate ratio does have a major effect on insulin levels.(1)

In summary, Ms. Liebman has done a great disservice to your readers by not understanding the contents of my book, in addition to having not carefully read the papers she so eagerly quotes to "justify" her preconceived notions about what constitutes a "healthy" diet....

(1) Amer. J. Clin. Nutr. 63: 174, 1996.

(2) Lancet ii: 155, 1956.

"It is excess insulin that makes you fat," writes Barry Sears. And since eating too many carbohydrates raises insulin, people should eat fewer carbs. Nice theory. But what's the evidence?

Sears only cites one piece of research: a "classic study published in Lancet nearly 40 years ago" in which people reportedly gained weight on a very-low-calorie diet that was mostly carbohydrate.

But he neglects to mention that the 14 patients were on each diet for only five to nine days. Nor does he mention that the data were questionable. As the study's authors put it:

"In such a study the difficulties are formidable. The first and main hazard was that many of these patients had inadequate personalities. At worst they would cheat and lie, obtaining food from visitors, from trolleys touring the wards, and from neighbouring patients. (Some required almost complete isolation.) At best they cooperated fully but a few found the diet so trying that they could not eat the whole of their meals. When this happened the rejected part was weighed, and the equivalent calories and foodstuffs were added to a meal later in the day. The results we report are selected, a considerable number of known failures in discipline being discarded."

By 1960, two longer-term studies had tried to replicate the 1956 results. Both failed.(1,2) Their conclusion: Cutting calories--not carbs--is what counts.(3) (Cutting fat may also help, if it leads people to eat fewer calories.)

Perhaps the best study is the one Sears cites by Gerald Reaven, in which 43 obese patients were fed in the hospital for six weeks.(4) It found no difference in weight loss with lower- or higher-carbohydrate diets. Sears says that's because both diets were low enough in carbohydrate to lower insulin. Yet the study says that "neither insulin nor [triglycerides] fell significantly in response to the higher-carbohydrate diet."

We asked Sears to send us studies showing that high-carbohydrate diets lead to more weight gain--or less weight loss--than low-carb diets. He sent only the flawed Lancet study.

Sears says that we've gotten fatter because we eat more carbohydrates than we did in the 1970s. But calories went up, too, and all the evidence--apart from the Lancet study--indicates that calories, not carbs, made the difference.

CARBOHYDRATES RAISE INSULIN

"Sears is right when he says that--for some people--a very-high-carbohydrate diet can raise insulin levels... and that high insulin levels raise the risk of heart disease," we wrote last July.

The question isn't whether carbohydrates can raise insulin. It's whether keeping insulin "in the zone" will help you "lose weight permanently," as Sears's book promises. In fact, studies suggest that if you're already fat, excess insulin may actually keep you from getting fatter.

"If an increase in insulin occurs from an increase in body fatness, its effect is different than if you come to my lab and I infuse insulin into your blood," says Angelo Tremblay, an obesity expert at Laval University in Ste-Foy, Quebec.

That's because in many--though not all--overweight people with excess insulin, the insulin loses its effectiveness. They become "insulin-resistant." And, assuming they don't have diabetes, people who are insulin-resistant may be less, not more, likely to gain weight.(5,6)

"High insulin levels are the body's last card to play to promote a stable body weight when exposed to a fattening environment," explains Tremblay.

Does that mean that excess insulin is good? No way.

"There's a price to pay," says Tremblay. High insulin levels increase the risk of diabetes, high blood pressure, and heart disease.

But it does mean that Sears's dogma--carbs raise insulin, and insulin causes obesity--is flawed.

"Insulin promotes fat storage," says Robert Eckel, an insulin expert at the University of Colorado Health Sciences Center in Denver. "But the fact that insulin goes up doesn't change body weight."

(1) Lancet i: 856, 1960.

(2) Lancet i: 1048, 1960.

(3) J. Amer. Med Assoc. 224: 1415, 1973.

(4) Amer. J. Clin. Nutr. 63: 174, 1996.

(5) Journal of Clinical Investigation 88: 168, 1991.

(6) Arner. J. Clin. Nutr. 61: 827, 1995.

RELATED ARTICLE

Do lower-carbohydrate diets keep you slim and healthy? Last July, we ran an article by Bonnie Liebman that critiqued those diets, and especially the best-selling The Zone ($24, 1995, HarperCollins, New York). Most of the two dozen letters we received were anything but complimentary.

"Amongst the most appalling examples of 'scientific' journalism I've seen in a long time:" wrote one reader. "It exemplified to me classic 'closed mind' or 'my way or no way:'" said another.

We also received a letter from Zone author Barry Sears that was too long to print in full. On page 10 is an excerpt from that letter. On page 11 is a response from Bonnie Liebman.

To those readers who have lost weight and feel better after switching to The Zone or other low-carbohydrate diets that cut calories: We wish you well. But we heard the same claims during other diet crazes--like Fit for Life in the 1 980s and The Dr. Atkins Diet Revolution during its first wave in the 1 970s. You'll lose weight on any diet that cuts calories. The trick is to keep it off.

As for new ideas: We're open to any that are supported by solid scientific evidence. Unfortunately, The Zone isn't.

COPYRIGHT 1997 Center for Science in the Public Interest
COPYRIGHT 2004 Gale Group