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Part 3.....

Leibel and his colleague Michael Rosenbaum have pioneered much of what we know about the body’s response to weight loss. For 25 years, they have meticulously tracked about 130 individuals for six months or longer at a stretch. The subjects reside at their research clinic where every aspect of their bodies is measured. Body fat is determined by bone-scan machines. A special hood monitors oxygen consumption and carbon-dioxide output to precisely measure metabolism. Calories burned during digestion are tracked. Exercise tests measure maximum heart rate, while blood tests measure hormones and brain chemicals. Muscle biopsies are taken to analyze their metabolic efficiency. (Early in the research, even stool samples were collected and tested to make sure no calories went unaccounted for.) For their trouble, participants are paid $5,000 to $8,000.

Eventually, the Columbia subjects are placed on liquid diets of 800 calories a day until they lose 10 percent of their body weight. Once they reach the goal, they are subjected to another round of intensive testing as they try to maintain the new weight. The data generated by these experiments suggest that once a person loses about 10 percent of body weight, he or she is metabolically different than a similar-size person who is naturally the same weight.

The research shows that the changes that occur after weight loss translate to a huge caloric disadvantage of about 250 to 400 calories. For instance, one woman who entered the Columbia studies at 230 pounds was eating about 3,000 calories to maintain that weight. Once she dropped to 190 pounds, losing 17 percent of her body weight, metabolic studies determined that she needed about 2,300 daily calories to maintain the new lower weight. That may sound like plenty, but the typical 30-year-old 190-pound woman can consume about 2,600 calories to maintain her weight — 300 more calories than the woman who dieted to get there.

Scientists are still learning why a weight-reduced body behaves so differently from a similar-size body that has not dieted. Muscle biopsies taken before, during and after weight loss show that once a person drops weight, their muscle fibers undergo a transformation, making them more like highly efficient “slow twitch” muscle fibers. A result is that after losing weight, your muscles burn 20 to 25 percent fewer calories during everyday activity and moderate aerobic exercise than those of a person who is naturally at the same weight. That means a dieter who thinks she is burning 200 calories during a brisk half-hour walk is probably using closer to 150 to 160 calories.

Another way that the body seems to fight weight loss is by altering the way the brain responds to food. Rosenbaum and his colleague Joy Hirsch, a neuroscientist also at Columbia, used functional magnetic resonance imaging to track the brain patterns of people before and after weight loss while they looked at objects like grapes, Gummi Bears, chocolate, broccoli, cellphones and yo-yos. After weight loss, when the dieter looked at food, the scans showed a bigger response in the parts of the brain associated with reward and a lower response in the areas associated with control. This suggests that the body, in order to get back to its pre-diet weight, induces cravings by making the person feel more excited about food and giving him or her less willpower to resist a high-calorie treat.

“After you’ve lost weight, your brain has a greater emotional response to food,” Rosenbaum says. “You want it more, but the areas of the brain involved in restraint are less active.” Combine that with a body that is now burning fewer calories than expected, he says, “and you’ve created the perfect storm for weight regain.” How long this state lasts isn’t known, but preliminary research at Columbia suggests that for as many as six years after weight loss, the body continues to defend the old, higher weight by burning off far fewer calories than would be expected. The problem could persist indefinitely. (The same phenomenon occurs when a thin person tries to drop about 10 percent of his or her body weight — the body defends the higher weight.) This doesn’t mean it’s impossible to lose weight and keep it off; it just means it’s really, really difficult.

Lynn Haraldson, a 48-year-old woman who lives in Pittsburgh, reached 300 pounds in 2000. She joined Weight Watchers and managed to take her 5-foot-5 body down to 125 pounds for a brief time. Today, she’s a member of the National Weight Control Registry and maintains about 140 pounds by devoting her life to weight maintenance. She became a vegetarian, writes down what she eats every day, exercises at least five days a week and blogs about the challenges of weight maintenance. A former journalist and antiques dealer, she returned to school for a two-year program on nutrition and health; she plans to become a dietary counselor. She has also come to accept that she can never stop being “hypervigilant” about what she eats. “Everything has to change,” she says. “I’ve been up and down the scale so many times, always thinking I can go back to ‘normal,’ but I had to establish a new normal. People don’t like hearing that it’s not easy.”

What’s not clear from the research is whether there is a window during which we can gain weight and then lose it without creating biological backlash. Many people experience transient weight gain, putting on a few extra pounds during the holidays or gaining 10 or 20 pounds during the first years of college that they lose again. The actor Robert De Niro lost weight after bulking up for his performance in “Raging Bull.” The filmmaker Morgan Spurlock also lost the weight he gained during the making of “Super Size Me.” Leibel says that whether these temporary pounds became permanent probably depends on a person’s genetic risk for obesity and, perhaps, the length of time a person carried the extra weight before trying to lose it. But researchers don’t know how long it takes for the body to reset itself permanently to a higher weight. The good news is that it doesn’t seem to happen overnight.

“For a mouse, I know the time period is somewhere around eight months,” Leibel says. “Before that time, a fat mouse can come back to being a skinny mouse again without too much adjustment. For a human we don’t know, but I’m pretty sure it’s not measured in months, but in years.”

Nobody wants to be fat. In most modern cultures, even if you are healthy — in my case, my cholesterol and blood pressure are low and I have an extraordinarily healthy heart — to be fat is to be perceived as weak-willed and lazy. It’s also just embarrassing. Once, at a party, I met a well-respected writer who knew my work as a health writer. “You’re not at all what I expected,” she said, eyes widening. The man I was dating, perhaps trying to help, finished the thought. “You thought she’d be thinner, right?” he said. I wanted to disappear, but the woman was gracious. “No,” she said, casting a glare at the man and reaching to warmly shake my hand. “I thought you’d be older.”

If anything, the emerging science of weight loss teaches us that perhaps we should rethink our biases about people who are overweight. It is true that people who are overweight, including myself, get that way because they eat too many calories relative to what their bodies need. But a number of biological and genetic factors can play a role in determining exactly how much food is too much for any given individual. Clearly, weight loss is an intense struggle, one in which we are not fighting simply hunger or cravings for sweets, but our own bodies.

While the public discussion about weight loss tends to come down to which diet works best (Atkins? Jenny Craig? Plant-based? Mediterranean?), those who have tried and failed at all of these diets know there is no simple answer. Fat, sugar and carbohydrates in processed foods may very well be culprits in the nation’s obesity problem. But there is tremendous variation in an individual’s response.

The view of obesity as primarily a biological, rather than psychological, disease could also lead to changes in the way we approach its treatment. Scientists at Columbia have conducted several small studies looking at whether injecting people with leptin, the hormone made by body fat, can override the body’s resistance to weight loss and help maintain a lower weight. In a few small studies, leptin injections appear to trick the body into thinking it’s still fat. After leptin replacement, study subjects burned more calories during activity. And in brain-scan studies, leptin injections appeared to change how the brain responded to food, making it seem less enticing. But such treatments are still years away from commercial development. For now, those of us who want to lose weight and keep it off are on our own.

One question many researchers think about is whether losing weight more slowly would make it more sustainable than the fast weight loss often used in scientific studies. Leibel says the pace of weight loss is unlikely to make a difference, because the body’s warning system is based solely on how much fat a person loses, not how quickly he or she loses it. Even so, Proietto is now conducting a study using a slower weight-loss method and following dieters for three years instead of one.

Given how hard it is to lose weight, it’s clear, from a public-health standpoint, that resources would best be focused on preventing weight gain. The research underscores the urgency of national efforts to get children to exercise and eat healthful foods.

But with a third of the U.S. adult population classified as obese, nobody is saying people who already are very overweight should give up on weight loss. Instead, the solution may be to preach a more realistic goal. Studies suggest that even a 5 percent weight loss can lower a person’s risk for diabetes, heart disease and other health problems associated with obesity. There is also speculation that the body is more willing to accept small amounts of weight loss.

But an obese person who loses just 5 percent of her body weight will still very likely be obese. For a 250-pound woman, a 5 percent weight loss of about 12 pounds probably won’t even change her clothing size. Losing a few pounds may be good for the body, but it does very little for the spirit and is unlikely to change how fat people feel about themselves or how others perceive them.

So where does that leave a person who wants to lose a sizable amount of weight? Weight-loss scientists say they believe that once more people understand the genetic and biological challenges of keeping weight off, doctors and patients will approach weight loss more realistically and more compassionately. At the very least, the science may compel people who are already overweight to work harder to make sure they don’t put on additional pounds. Some people, upon learning how hard permanent weight loss can be, may give up entirely and return to overeating. Others may decide to accept themselves at their current weight and try to boost their fitness and overall health rather than changing the number on the scale.

For me, understanding the science of weight loss has helped make sense of my own struggles to lose weight, as well as my mother’s endless cycle of dieting, weight gain and despair. I wish she were still here so I could persuade her to finally forgive herself for her dieting failures. While I do, ultimately, blame myself for allowing my weight to get out of control, it has been somewhat liberating to learn that there are factors other than my character at work when it comes to gaining and losing weight. And even though all the evidence suggests that it’s going to be very, very difficult for me to reduce my weight permanently, I’m surprisingly optimistic. I may not be ready to fight this battle this month or even this year. But at least I know what I’m up against.

End of article.