Fat: What the Experts Don't Know About Obesity

By Maggie Mahar, Health Beat. Posted December 5, 2008.

Why leptin resistance occurs in some people is poorly understood, Friedman says. It may be a relic of the thrifty-gene response, ramping up appetite in those whose ancestors lacked adequate food. The Rockefeller team measured leptin levels in the Kosraean population; Friedman is using that data to help correlate leptin resistance with genes that might be responsible for it. According to Friedman, each of us has a ‘set point' of hunger and satiation, which we inherited from our individual forebears. "We are born with this setting, and we are driven to keep eating until we reach it."

"People whose ancestors, like most Kosraens', had to work hard to get enough to eat, had their hunger-volume -- analogous to a specific setting on a radio dial -- turned up to 8 or 10." Chronicle reporter Duncan says. "Those whose ancestors had plenty of food -- for instance, the agriculturists of the Fertile Crescent and Europe, and parts of India and China, people who have basically had stable food supplies for as many as 10,000 years -- have inherited a setting of 2 or 3."

Friedman concedes that more work is needed to understand the role of exercise in weight gain. But, according to the MIT Technology Review, he does believe that "the weight increases of the past 20 years in the United States represent a steady progression of people eating enough food to reach their set points, rather than a sudden spike in bad eating habits or more sitting around." What really intrigues Friedman is why everyone doesn't get chubby when there is plenty to eat. Analyses show that the number of lean people has remained steady for the past 30 years, he says. "One's size is not an environmental effect. Nor is it a matter of willpower.'"

There is of course much money to be made if entrepreneurs can convince the obese that they have the secret to weight loss. As Duncan notes, "the diet industry [is] skeptical of Friedman's claim that obesity is as overdetermined [as he claims. The industry] insists that people can overcome the hunger impulse and trim down with healthy diets and reduced calories. Friedman says this is true, but that even a heavy person in most cases can lose only 10 or 20 pounds and keep it off. But even a small amount of weight loss can be healthy, he says. ‘You can lose more for a period of time,' he says, but the biology will eventually force you to eat in most cases, and ‘you will regain the weight.'

"Friedman acknowledges that what he suggests is counterintuitive, since people can resist jelly beans up to a point. But he insists that, for the majority of the obese, free will in weight control is an illusion. ‘This is a way of thinking that needs to change.' "

One might wonder why the thrifty gene has survived. After all, how many Americans die because they don't get enough food? Granted, many of America's poor are malnourished, which in turn leads to diseases that can be fatal, but few succumb because they simply can't get enough calories.

But as the documentary Fat points out, Americans "have gone from having very little to eat to being able to eat a lot -- with a few bucks in our pocket -- in just 75 years."

Panning a fast-food restaurant, the film points out how many calories you can get for just $4. This wasn't true during the Great Depression of the 1930s. Indeed, the film's narrator observes "there are millions of people who are here today who wouldn't have been here 60 years ago," because they couldn't have "gotten this much food for that amount of money in yesterday's dollars." 

Little wonder that the brain still sounds an alarm when we lose weight.

What We Are Learning From Gastric Bypass Surgery

And leptin resistance is just one of many mechanisms that protects us.

"The gut has a nervous system -- and a mind of its own -- that decides what and how much we eat," says Michael Gershon, a bowel expert at Columbia University and author of the 1998 book The Second Brain, who appears in Fat.

At Massachusetts General, Dr. Lee Kaplan agrees: "We have two brains -- in the stomach and ‘upstairs.' The brain in the gut can disturb the brain in the head."

"Neurochemical signals flow between the two brains," Kaplan says, "And we have discovered that gastric bypass surgery interrupts that flow."

Until recently, physicians believed that patients lost weight because the surgery reduced the size of the stomach, forcing them to eat less. But once again, it's not that simple. Researchers performing gastric bypass surgery on rats have discovered that the surgery severs nerves in the bowel that communicate with the brain -- and that this is tied to weight loss.

Today, the surgery is giving researchers valuable new information about how the brain and gut manage obesity.

See more stories tagged with: health, fat, obesity

Maggie Mahar is a fellow at the Century Foundation and the author of Money-Driven Medicine: The Real Reason Health Care Costs So Much (Harper/Collins 2006).

Liked this story? Get top stories in your inbox each week from Health and Wellness! Sign up now »