Ahh, the post-holiday season – time to take down the Christmas tree before it starts a fire, and to figure out how to combat the after effects of all that pumpkin pie. We are barraged with success stories promoting the best way to lose weight, but even with the $30 billion spent annually by Americans on weight loss products, most people end up regaining the weight in a few years. Keeping that weight off can be a struggle, and a recent study has helped to shed some light on what your body is doing to make it so difficult.
Researchers in Melbourne put 50 overweight or obese people on a very-low-calorie diet for 8 weeks. Most of them lost a substantial amount of weight –at least 10% of their starting weight. After they lost the weight, the researchers followed these individuals for another year while they attempted to maintain their slimmer figures. The researchers weren’t just interested in whether the dieters regained the weight, but if so, why the weight returned.
In addition to subjective measurements like feelings of hunger or thoughts about food, the researchers also measured levels of hormones and other factors within the body that influence appetite. Not surprisingly, levels of hormones related to appetite and energy expenditure were abnormal after losing weight. The more interesting finding, though, was that even a year after losing weight the levels did not return to normal. Basically, their bodies were still acting as if they were starving.
For example, levels of leptin, a hormone that tells your brain when you’ve had enough to eat, were reduced after weight loss, making people hungrier. Even a year after losing weight, though, leptin levels were still lower than before they started the diet. Levels of another hormone called ghrelin – this one actually stimulates hunger – increased during weight loss. While ghrelin levels decreased somewhat after subjects stopped dieting, they still remained higher than normal even a year after the weight had been lost.
As you can imagine, these biological changes in response to weight loss make it hard to keep off lost weight. While this would be helpful to someone who actually was starving, it is obviously very inconvenient for someone trying to maintain a healthy weight after dieting. It makes it clear that weight maintenance is not simply an issue of willpower, but rather an active fight against your body. Although there aren’t yet medications available that can counteract all these changes that occur in response to dieting, knowing just how important they are should spur on more research exploring this area. (Here’s a nice article exploring the difficulty of keeping weight off, and what this research means for someone trying to lose weight).