As anyone who has ever tried to lose weight can attest, keeping weight off is often harder than losing it in the first place. Research suggests that the hormone leptin may be responsible. When individuals lose weight, their levels of leptin drop, too. In response to this leptin “deficiency,” the body burns fewer calories and coordinates various body systems to regain the lost weight.

As reported in an article published in the December 2005 Journal of Clinical Investigation , researchers studied what would happen if they restored levels of leptin in people who had lost weight to levels that were present prior to their dieting. They found that once circulating levels of leptin had been restored to pre-weight loss levels, the body changes that opposed the maintenance of weight loss reversed as well.

About the Study

The researchers recruited five men and five women who had maintained their usual weights for six months, and tested the metabolic systems responsible for regulating body weight in these individuals. The study subjects then lost 10% of their body weight and were put on a liquid diet designed to maintain their new weights. When their weights stabilized, they again underwent metabolic testing. Finally, the researchers kept the participants on diets designed to maintain their lost weight while giving them leptin supplements that restored their levels of leptin to pre-weight loss levels. The participants then underwent testing for a third time.

The researchers found that most of the metabolic changes that occurred after weight loss (and which work to regain lost weight) actually reversed when levels of leptin were restored to pre-weight loss levels.

When considering these results, it is important to keep in mind that this study included only ten participants, and the researchers did not assess the long-term effects of leptin on the subjects’ actual weight.

How Does This Affect You?

When we lose weight, our leptin levels drop too. This study demonstrated that restoring leptin to pre-weight loss levels reverses the changes that act to restore the lost weight. This suggests that leptin may one day be effective as a weight-loss maintenance drug.

As if it isn’t difficult enough to overcome outside temptations (like chocolate or a comfy couch!), it seems unfair that our own bodies would work against us when it comes to maintaining lost weight. In the end, as with so many things, it comes down to balance. By eating appropriate amounts of healthful foods and maintaining an active lifestyle, each of us must strive to balance the calories we ingest against those we expend—even if our own bodies would have it otherwise.