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Health Sense

Let the post-diet era begin

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Email|Print| Text size + By Judy Foreman
October 1, 2007

Is permanent, significant weight loss really possible?

If you're talking merely 10 to 20 pounds - and nobody knows the actual figure - you probably can diet and exercise your way to a svelter self and stay there, provided you stick with your weight control program rigorously. Forever.

But if you're among the two-thirds of adult Americans who are overweight or obese, permanent, substantial weight loss appears to be almost impossible by diet and exercise alone.

Only about 1 to 2 percent of obese people can permanently lose weight through diet and exercise alone, said Dr. Lee Kaplan , director of the weight center at Massachusetts General Hospital.

"Dieting is like holding your breath," he said. "You can do it, but not for long. Your body is stronger than your willpower."

In other words, Americans have probably wasted way too much time, money, and hope on diet programs that don't help enough. It still makes sense, however, to eat as healthily as you can and to do whatever you can to avoid gaining any more weight.

One famous study conducted at the University of Minnesota during World War II illustrates the ineffectiveness of severe dieting. The researchers put 36 physically and emotionally healthy young men of normal weight on a strict diet, allowing them only half the calories they were used to. The men lost weight, but became psychological wrecks, obsessing about food, bingeing, and, even after the diet was over, eating way too much, often 8,000 to 10,000 calories a day until they regained the weight, recounted New York Times science writer Gina Kolata in her recent book, "Re-thinking Thin."

In another classic study in the 1950s, researchers at Rockefeller University in New York City recruited obese people who were so desperate to lose weight that they agreed to live in the hospital for eight months, including a four-month period in which they subsisted on only 600 calories a day of liquid formula. They lost weight, Kolata noted. But, to the dismay of subjects and researchers, they all quickly regained the weight.

That's because the basic biochemistry of the body's weight management system can work against even highly motivated dieters.

When a very fat person loses a lot of weight by diet and exercise, the brain goes into panic mode, reading a complex array of chemical signals as proof of impending starvation. Metabolism slows. The body hangs on to every calorie it can get. The chemical signals that trigger appetite soar, creating a drive to eat so powerful you can't resist. From the standpoint of evolution, this makes sense: Our DNA was built when we were hunter-gatherers to protect us against starvation, not obesity.

Consider one of the best-studied weight control hormones, leptin, which is made in fat cells and is designed to tell the brain: "Stop eating. I'm full."

"Obese people usually have high levels of leptin because they have so many fat cells making it," said Dr. Eleftheria Maratos-Flier, an obesity researcher and associate professor of medicine at Beth Israel Deaconess Medical Center. "The heavier you are, the higher the circulating leptin." In theory, being fat should mean that the brain would be flooded with "stop eating" signals.

But when people go on severe diets, "they lose more leptin than you would expect. So the brain thinks there is less fat than there ought to be," which makes people eat more, she said.

And leptin is just one of many hormones involved in weight control. "In the stomach and intestines alone," Kaplan said, "there are 36 hormones that regulate weight, and another 30 in the brain. The end result of all these chemicals is to keep our energy stores, that is, fat, in balance."

Put differently, some researchers believe that one reason weight loss programs ultimately fail is that diet and exercise do not change the body's "set point," the thermostat-like mechanism in the hypothalamus and other parts of the brain that keep weight fairly constant.

Dr. David Heber, director of the UCLA Center for Human Nutrition, is more optimistic about the effectiveness of dieting. "The set point can be changed. Yes, there are signals to eat and to hoard fat, but having said that, humans do adapt to starvation and do change," he said. While the hormones that control appetite and satiety do tilt the equation toward regaining lost weight, "psychology trumps physiology. I see people every day who have overcome their genes and kept their excess weight off for decades."

Many researchers do agree that one weight loss strategy does seem to change the set point - bariatric surgery, the stomach-stapling procedure. Doctors used to think it worked by simply reducing the size of the stomach, preventing people from eating much. Now, they think it works because, with less stomach tissue pumping out hormones such as ghrelin, which stimulates appetite, a person's appetite and satiety signals may be altered to help them eat less.

So if dieting sets up a battle between our free will and our hormones, are America's fat masses wasting their time desperately trying to lose weight?

To some, including the National Association to Advance Fat Acceptance, a civil rights organization that is fighting discrimination against fat people, all this suggests not so much a hopeless message as a liberating one. "Most people do not choose to be fat," said the group spokeswoman, Peggy Howell. "But once people are fat, it is next to impossible to change that. It's far healthier to accept who you are and get on with your life than to be obsessed with what goes into your mouth."

That makes a lot of sense to me, though I resist the idea that our genes are the big culprits because we have basically the same genes today that our skinnier grandparents had. What's changed is our lifestyles - more sitting around eating Twinkies, less walking to and from daily activities.

So, here's my take. Because of the body's complex biochemistry, it's very difficult to lose weight once you gain it. So, exercise as much as you can - for general health, in addition to weight control. Eat right - fewer refined carbs, more fruits and veggies - again, for general health. If you're fat, don't just blame your genes and let yourself get fatter and fatter.

At the same time, be gentle with yourself, and with fat people you see.

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