According to a study in the New England Journal of Medicine, a shortage of willpower may not be the only reason for this rebound weight gain. Hunger-related hormones disrupted by dieting and weight loss can remain at altered levels for at least a year, fueling a heartier-than-normal appetite and thwarting the best intentions of dieters.
Lead researcher Joseph Proietto, PhD, a professor of medicine at the University of Melbourne's Heidelberg Repatriation Hospital, in Victoria, Australia states that, "Maintaining weight loss may be more difficult than losing weight." "This may be due to biological changes rather than [a] voluntary return to old habits."
Scientists have known for years that hormones found in the gut, pancreas, and fatty tissue strongly influence body weight and processes such as hunger and calorie burning. And the reverse is also true: a drop in body fat percentage, for instance, causes a decrease in the levels of certain hormones (such as leptin, which signals to your brain when you're full) and an increase in others (such as ghrelin, which stimulates hunger).
What wasn't so well known, until now, was whether these changes in hormone levels persist after an individual loses weight. To find out, Proietto and his colleagues put 50 overweight or obese men and women on a very low-calorie diet for 10 weeks, then tracked their hormone levels for one year.
The average weight loss during the initial diet period was about 30 pounds, which for most of the participants represented at least 10% of their starting body weight. (Seven people who did not meet this target were dismissed from the study.) Blood tests showed that average levels of several hormones (including leptin, ghrelin, and insulin) had changed as a result of the weight loss. As expected, the participants also reported being hungrier -- both before and after breakfast -- than they had been at the study's start.
At the 10-week mark the participants were allowed to resume a normal diet, but they continued to receive periodic advice from a dietitian and were also encouraged to get 30 minutes of exercise most days of the week. One year later, they'd regained about 12 pounds, on average, and follow-up tests showed that their hormone levels had only partially stabilized. Their hunger levels remained elevated as well.
New England Journal of Medicine, Oct 2011