Many people gain weight when they stop smoking, and, for that reason, they may light up again. Also, it is not a given that everyone who quits smoking gains weight. Regardless, you can strategize to fend off unwanted pounds. Nicotine suppresses the appetite and causes the liver to release glycogen, which raises the blood sugar level slightly. With nicotine out of your system, you may feel hungry more often.
Smoking artificially elevates heart rate and increases metabolism.
When you stop smoking, your body has to readjust to a lower metabolic rate. Smoking dulls the taste buds. Use common sense to maintain your weight while quitting smoking. Obviously, if you substitute a candy bar each time you crave a cigarette, you will gain weight. If you think this won't be enough, figure out your current average daily caloric intake and use this as a guideline for weight maintenance after you quit.