Yo-yo dieting can affect appetite hormones for up to a year

By Dr. Ananya Mandal, MDOct 27 2011

A new study suggests that the ‘yo-yo’ effect that dieters experience of shedding pounds and gaining them back may be due to the persistence of hormones that drive the urge to eat even a year after weight loss.

For the study the researchers tracked weight loss 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, said the study published today in the New England Journal of Medicine.

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.

It has been known that the body reacts 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.

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. “Indeed, the most difficult part of the weight loss program is the maintenance phase, which may be indefinite.”

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.

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 reduce, few maintain the lower weight, Proietto 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. 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.

“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.” “People who regain weight should not be harsh on themselves, as eating is our most basic instinct,” said Proietto.

People who lose less than 10 percent of body weight would probably show the same thing to a lesser degree, said Dr. George Bray of the Pennington Biomedical Research Center in Baton Rouge, La. Bray concluded from this study, “It's better not to gain weight than to try to lose it.”