By Tom Valeo
Doctors tell overweight patients that the secret to losing weight is simple: Consume fewer calories than your burn.
What they often fail to mention, however, is how ferociously the body fights to regain the weight it loses. An inadequate supply of calories, which forces the body to burn fat and muscle for energy, triggers a cascade of physical and psychological changes that rev up the appetite, slow down the metabolism and virtually guarantee that the lost weight will be regained, perhaps as quickly as a year.
Dr. Arya M. Sharma, a Canadian obesity researcher at the University of Alberta in Edmonton, tells his patients a different story.
"Obesity is a chronic condition," he said. "Once you have obesity, you have it for life. You can treat obesity, but there's no short-term fix. A diet, a personal trainer — you can do lots of things for a few weeks and lose weight, but if you can't do those things forever, the weight will come right back."
Obesity, in other words, is like having diabetes or heart disease or arthritis, according to Sharma — you must deal with it every day if you have any hope of controlling it.
"You need to get obsessed about your weight," said Sharma, the scientific director of the Canadian Obesity Network. "You need to exercise every day; you need to count your calories at every meal. These are things you must do. If you find a way to control your obesity — a 3-mile walk or run every day, for example, or cutting out all soda, or all carbs — you have to keep doing that. If you ever stop, the weight will come right back."
Weight loss spurs the brain, the liver, the endocrine system, the muscles and other systems to seek out more calories and conserve the calories the body consumes, Sharma said. That's what produces the notorious plateau that plagues those who are trying to lose weight. The weight loss suddenly stops, and may start creeping upward. Evolution has created a body that unleashes a cascade of changes to cope with inadequate calorie consumption.
As fat cells shrink, for example, they produce less leptin, the hormone that informs the brain that the body has had enough to eat.
"When leptin goes down the brain thinks it must start restoring the body's fat deposits," Sharma said.
As a result, appetite grows into a gnawing desire to eat that easily overwhelms willpower.
Meanwhile, the muscle cells produce less energy, and the hypothalamus deep in the brain slows the metabolism to conserve calories. The liver, which modulates levels of glucose and fat in the blood, contributes to this process.
"Weight loss even appears to alter how the gut absorbs food," Sharma said. "It may have an impact on gut bacteria, which are important for digestion. The body's trying to get the weight back."
So what's the solution? More willpower?
Bradley Appelhans, an obesity researcher at Rush Medical College in Chicago, argues that willpower is no match for other brain processes that encourage overeating.
In a paper published in the August Journal of the American Dietetic Association, Appelhans says the simple pleasure produced by the taste of food, which is abundant in modern society, easily overwhelms the impulse control exercised by the prefrontal cortex, the part of the brain right behind the forehead that provides the "will" in "willpower."
"The taste and pleasure of food can override feeling full," he said. "The brain's reward circuit can override feelings of satiety. So you go out to a restaurant and eat a full meal, and your hypothalamus receives signals from the body that you've had enough food, and you feel satiety. Then the waiter brings out the dessert platter, and the sight of dessert stimulates the reward circuit, and it overrides that sense of satiety, and you order dessert."
On top of that, we're all prone to "time discounting," the tendency to prefer immediate gratification over future rewards.
"Most of us would rather receive $200 today than $300 a year from now," he said.
The best way to keep weight off, according to Appelhans, who has lost an unwanted 10 to 15 pounds and kept it off for several years, involves helping the brain do the right thing. Keep fattening foods out of the house, for example, and shop with a grocery list that will discourage you from making impulse purchases. Find a way to alleviate stress, which promotes overeating by increasing the appeal of calorie-rich "comfort" foods. Don't challenge your willpower with buffets and all-you-can-eat restaurants. And when trying to lose weight, focus on short-term behavioral goals, such as cooking a healthy dinner tonight, rather than long-term goals, such as losing 10 pounds by Christmas.
Tom Valeo writes frequently about health matters. He can be reached at firstname.lastname@example.org.