According to some studies, weight loss is an important reason people smoke- particularly women.

Smoking may increase resting metabolic rate (the rate at which people burn calories) and in some cases, smoking increases levels of thyroid hormones that also may boost metabolism.

Scientists studied the effects of 1 hour of passive smoke inhalation on 18 men and women in an environmental chamber filled with cigarette smoke to simulate a bar.

Researchers from Greece found that secondhand smoke also increases metabolism and thyroid hormone secretion.

Passive smoking, however, also increases the risk of cancer, lung disease and heart disease, so hanging out in smoke-filled bars is definitely not a good idea even if you need to lose some weight. [sources: Journal of Clinical Endocrinology & Metabolism, Fitness RX]