Obesity studies for years have shown that when overweight people lose weight their metabolism slows and they experience hormonal changes that increase appetite, a finding that has been backed by new Australian research that shows those changes persist for a longer period of time.
Scientists theorized that these biological changes could explain why most obese dieters quickly gain back much of their weight that they had previously lost. They found that for at least a year, subjects who lost weight on a low-calorie diet were hungrier than when they started and had higher levels of hormones telling the body to eat more, conserve energy and store fuel as fat.
The study, published Wednesday in the New England Journal of Medicine, recruited 50 healthy people who were either overweight or obese and put them on a 10-week highly restricted diet that led them to lose at least ten percent of their body weight. The participants were then kept on a diet to maintain that weight loss.
On average, participants lost about 30 pounds during the study period, faster than the standard advice of losing 1 to 2 pounds per week. They took in 500 to 550 calories per day on the OptiFast plus vegetables diet for eight weeks. The last two weeks of the study they were gradually reintroduced to ordinary foods.
However, only 34 people lost as much as the plan called for and stuck with the study long enough for researchers to analyze the data. After a year, researchers discovered that the participants´ metabolism and hormone levels had not returned to the levels before the study began.
And despite counseling and written advice about how to maintain their new weights, they gained an average of 12 pounds back over that year. So they were still at lower weights than when they started.
The findings suggest that dieters who regained their weight are not only slipping back into old eating habits, but are struggling against a persistent biological urge.
“People who regain weight should not be harsh on themselves, as eating is our most basic instinct,” Joseph Proietto of the University of Melbourne in Australia, lead author of the study, told USA Today in an email.
While it is no surprise that hormone levels changed shortly after the participants lost weight, “what is impressive is that these changes don´t go away,” Dr. Rudolph Leibel, an obesity researcher at Columbia, told the New York Times.
“It is showing something I believe in deeply – it is very hard to lose weight,” Dr. Stephen Bloom, an obesity researcher at Hammersmith Hospital in London, told Gina Kolota of the New York Times. And the reason, he said, is that “your hormones work against you.”
The researchers said that more than one solution to the crisis of obesity will most likely be necessary: “a combination of medicines” that will have to be safe for long-term use. However, drug companies have had a rough time getting weight loss and diet medications approved for market. The US Food and Drug Administration has rejected four different weight-loss drugs over the past four years. And has ordered the withdrawal of one prescription medication (Meridia) already on the market.
The study gives us a “very comprehensive” and “really discouraging” look into the breadth of the body´s response to weight loss, said Dr. Daniel Bessesen, an endocrinologist and obesity researcher at University of Colorado’s Denver Health Medical Center. It captures just how many resources the body musters to ensure that pounds are put back on – a long list of hormones that regulate appetite, feelings of fullness after eating and how calories are used.
As part of the study, Proietto and his team checked the blood levels of nine hormones that influence appetite. The major finding came from comparing the hormone levels from before the weight-loss program to one year after it was over. At the end of the study period, researchers found six hormones were still acting in a way that would boost hunger.
One hormone, leptin, which tells the brain how much body fat is present, fell by two-thirds immediately after the participants lost their weight. When leptin falls, appetite increases and metabolism slows. The team found one year out that leptin levels were still a third lower than they were when the study began, and leptin levels increased as subjects regained their weight.
Other hormones, including ghrelin and peptide YY, also changed a year out in a way that made the subjects´ appetites stronger than at the start of the program. Ghrelin levels increased and peptide YY decreased.
The team also had participants rate their hunger levels after meals at the one-year mark, compared to what they reported before the diet program started.
Experts not affiliated with the Australian study said the persistent effect of hormone levels was not surprising, and that it probably had nothing to do with the speed of weight loss.
People who lose less than 10 percent of their body weight would probably show similar hormonal changes, though to a lesser degree, Dr. George Bray of the Pennington Biomedical Research Center in Baton Rouge, Louisiana, told USA Today.
A key measure of the study is that “it´s better not to gain weight than try to lose it,” he added.
The results show that losing weight “is not a neutral event,” and that it is no accident that more than 90 percent of people who lose a lot of weight gain it back, said Leibel. “You are putting your body into a circumstance it will resist,” he said. “You are, in a sense, more metabolically normal when you are at a higher body weight.”
One solution might be to restore hormones to normal levels by giving drugs after dieters lose their weight. But it is possible, said Dr. Jules Hirsch of Rockefeller University, that researchers just do not know enough about obesity to prescribe solutions.
One thing is clear, he told the New York Times: “A vast effort to persuade the public to change its habits just hasn´t prevented or cured obesity.” More knowledge is needed, he added. “Condemning the public for their uncontrollable hedonism and the food industry for its inequities just doesn´t seem to be turning the tide.”
People who lose significant weight not only gain bigger appetite but also burn fewer calories than normal, creating “a perfect storm for weight regain,” Leibel said. Avoiding weight regain appears to be a fundamentally different problem from losing weight in the first place, and that researchers should pay more attention to it, he added.
The study was supported by the Australian government, medical professional groups and a private foundation. Proietto served on a medical advisory board of Nestle, maker of OptiFast, until last year.
Two-thirds of Americans are overweight or obese, and while obesity rates have begun to stabilize, there hasn´t been any real decline. Public health officials already fear that an entire generation of Americans will suffer poorer health and earlier deaths due to obesity.
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