What is the mechanism by which quitting smoking causes increased appetite?
What is the mechanism by which quitting smoking causes increased appetite?


Research has generally focused on weight gain, rather than increased appetite, since it's a more objective outcome.

Smoking cessation has been clearly and consistently shown to be associated with weight gain, in both retrospective and prospective studies, and nicotine replacement seems to reduce some, but not all of the effect, at least while it's used.

There is an excellent, though now aging review of both the effect and potential mechanisms behind a paywall by Filozof. One of the most cited early articles is free at NEJM. 

The mechanism of this weight gain is an active area of research, and, as discussed in Filozof, includes increased appetite with associated increase in calorie intake, decreased resting metabolic rate, and decreased physical activity.

Leptin, a hormone that increases both satiety and energy expenditure, is actually increased in people who stop smoking at the same time they are gaining weight. This finding has been convincingly demonstrated and replicated. Leptin insensitivity is a strong candidate for the primary driver of the increase in appetite (and weight gain) after smoking cessation.

Of course, since cigarette smoking causes profound changes in gene regulation, smoking cessation likely does as well. The full answer is almost certainly multifactorial.