A lot of people smoke because they think it curbs their appetite. While this might be a temporary side effect, nicotine actually acts as a stimulant. Instead of relaxing you, it puts more stress on your body. This triggers the release of the stress hormone, cortisol.
The presence of cortisol encourages your body to store fat around the midsection, a particularly unhealthy place for extra pounds go accumulate.
Likewise, drinking alcoholic beverages can contribute to fat storage. The sugar in alcohol causes your body to release insulin, rapidly dropping your blood glucose level and making you hungrier. Over time, insulin resistance can occur.