The off-and-on experience for dieters who shed pounds and gain them back may be due to the persistence of hormones that drive the urge to eat even a year after people lose weight, a study suggests.
Researchers tracked diet losses and changes in hormone levels in 50 people who agreed to consume only Nestle SA’s Optifast, and two cups of vegetables for 10 weeks. A year after the volunteers lost 10 percent of their weight, hormones that affect appetite -- including leptin and ghrelin -- continued to send signals urging the body to eat more, according to a study released yesterday in the New England Journal of Medicine.
Scientists have long known the body reacts vigorously to weight loss, lowering resting metabolism rates and tweaking levels of hormones, peptides and nutrients. The study followed physiological changes over time to measure how long the body’s response to a diet would last. The answer: At least a year.
People “who have lost weight need to remain vigilant and understand that once they have lost weight the battle is not over,” Joseph Proietto, professor of medicine at the University of Melbourne and a lead author, said in an e-mail. “Indeed, the most difficult part of the weight loss program is the maintenance phase, which may be indefinite.”
There are more than 1.5 billion overweight people in the world, including two of every three adult Americans, studies show. While cutting calories helps people slim down, few maintain the lower weight, Proietto said.
In normal times, leptin, a hormone produced by fat cells, sends signals to brain receptors to reduce food intake once a person is full, and boost metabolism. During the 10 weeks of the study’s diet, leptin levels plunged 65 percent. They remained 35 percent below their original levels a year later. The amount of ghrelin, which stimulates hunger, rose significantly with weight loss and remained higher at the end of the study.
The end result was that volunteers reported a significant increase in appetite while losing weight, and said they still felt hungry a year later, the researchers said. Similar fluctuations were recorded with a half-dozen other compounds believed to regulate appetite.
While it’s still not clear whether the changes are temporary or long-term, the study suggests the relapse rate “is not simply the result of the voluntary resumption of old habits,” the researchers said.
The findings also bolster the idea that each person has a “set-point” for their weight, and efforts to get below that level are vigorously resisted within the human body, the researchers said. If this is correct, safe, effective and long-term treatments are needed to counteract changes in hormone and reduce appetite, they said.
It’s not proven that the hormonal changes causes dieters to regain weight, said Donald Hensrud, the chairman of preventive medicine at the Mayo Clinic in Rochester, Minnesota, in a telephone interview. Researchers don’t know if the changes in hormone levels are appropriate given the weight fluctuation, or if they are driving appetite and weight back up, he said. Hensrud wasn’t involved in the study.
Additional studies, such as one comparing hormone levels from people who have lost weight to those who are a similar size and build who have weighed the same for years, would be helpful, he said in a telephone interview. Until researchers understand the hormone swings better and doctors can use the information to help patients shed pounds, overweight people should stick with the tried and true, he said.
“There are examples of people who have lost weight and maintained it,” Hensrud said. “Until we know more, we should continue to promote the things we know - sustainable lifestyle choices, physical activity and a healthy diet. We’re not ready to turn that upside down yet.”