It is no mystery that eating a healthy diet and exercising can make extra pounds disappear. But the results of a new study suggest that lifestyle changes may also lower levels of leptin, the "obesity hormone" thought to be involved in appetite regulation.

Fat cells and other tissues in the body produce leptin, which is believed to notify the brain to reduce appetite when fat cells are "full." Exactly how the hormone works to control appetite is uncertain, however.

Researchers found, not surprisingly, that exercise, a healthy diet or a combination of the two led to weight loss, including a reduction in body fat, during the one-year study.

The investigators also found that leptin levels declined significantly in men who made changes in diet, exercise or both. But when the researchers took into account the amount of fat lost during the study, they found that leptin levels dropped more than expected.

Long-term diet and exercise interventions may have direct effects on the plasma leptin concentration beyond the effect expected due to changes in fat mass.

Long-term reductions in leptin levels may somehow adjust the way the central nervous system regulates appetite and metabolism.

This adjustment may help maintain weight loss in the long run.

Since some researchers had hoped that giving people leptin might encourage weight loss, it may seem odd that the current study found that leptin levels decreased with weight loss. However, past studies have found that people who are obese do not lack the hormone, they actually have higher-than-normal levels.

American Journal of Clinical Nutrition 2001; 73: 240-245