Nicotine both speeds up your metabolism and depresses your appetite, meaning you feel less hungry when you smoke AND burn more calories. It’s not an accident that fashion models tend to be photographed with a cigarette in their hand.
When you quit, particularly if you go cold turkey, your appetite will suddenly go back to normal, making you feel hungry out of the blue. Most people also find that their sense of taste and smell improve, making food seem more appetizing on top it. This can be difficult in the short term, but does get better as you get used to it.
Ultimately, whether or not you gain weight depends on a lot of things, but the most important is whether or not you start to eat more after quitting. Snacking can be a big source of calories for people who are quitting, because they are replacing the hand-to-mouth action of smoking. Avoid snacks that are high in sugar and fat but low in nutrition, like sweets and chips. Instead, go for fruit, veggies, whole grain crackers, and foods that are high in protein, like a bit of low-fat cheese, nuts, or hummus. Exercise can also help, in addition to boosting your mood and improving sleep.
Medical review: Nathan Cobb, MD, November 15, 2017