A hormonal imbalance may help explain why the pounds dieters work so hard to lose come back so easily.

A new study suggests that our bodies have a hard time adjusting to weight loss and may activate internal systems to restore lost fat.

Body weight is regulated by a complex network of hormonal and metabolic systems. After weight loss, researchers say the body may interpret a newly svelte physique as deficient in the hormone leptin and jump-start processes to restore the body to its previous weight.

Leptin is a hormone commonly associated with obesity that plays a role in regulating weight and appetite.

Leptin May Keep Pounds From Coming Back

In the study, published in The Journal of Clinical Investigation, researchers examined the effects of leptin injections in people who recently lost weight and were trying to maintain their weight loss.

The results showed that most of the metabolic and hormonal changes that normally work against keeping the pounds off were reversed once leptin levels were restored to the levels before weight loss.

Researchers say those internal changes may help explain why more than 85 percent of obese people who lose weight eventually gain it back.

If further studies confirm these effects, researchers say the results suggest that targeting leptin may help people who have lost weight keep it off.

By Jennifer Warner, reviewed by Michael W. Smith, MD

SOURCES: Rosenbaum, M. The Journal of Clinical Investigation, December 2005; vol 115: pp 3579-3586. News release, Columbia University.