Weight gain-average amount is 5 to 8 pounds over 5 years (for some, there is no weight gain); the extra weight is not a health threat. A lot of it comes from comfort eating, trying to replace the oral fixation of smoking and having something in your mouth, plus the fact nicotine is actually an appetite supressant, so it would help you eat less.

Smoking effects a person’s metabolism and also burns calories:

• Smoking burns up to 200 calories a day in a heavy smoker
• Because smoking burns calories, metabolism is boosted (increased) slightly
• Nicotine is an appetite suppressant

When you quit smoking, a gain of between 5 and 10 pounds during the first few months of cessation is normal. If your eating habits have remained the same as they were when you smoked, you can easily shed this small gain with a brisk, 30 minute walk daily.

Have healthy snacks on hand! Put snacks together ahead of time so that when the munchies hit, you’ve got good food choices within easy reach:

• vegetable sticks - celery, carrot
• 94% fat free popcorn
• sunflower seeds in the shell
• Water - drink lots of it!
• hard candies to suck on
• fresh fruit
• fat free yogurt
• herbal teas
• hot cocoa made with nonfat milk
• frozen grapes
• fat free fudgecicles

I found carrot sticks to be the best solution, crunchy, tasty and healthy!

Try to avoid drinking alchohol, get a good 8 hours of sleep a night, take 30 minutes excercise every day.

A more technical explanation is that 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. If you eat the same as you did when you were smoking, your body will end up using less and storing more (as fat) of the food. Smoking dulls the taste buds. Food begins to taste better to new nonsmokers; this can increase food intake. And then there’s oral fixation — some ex-smokers may want something to fill the void of cigarettes.

More information here:

Quit Smoking Weight Gain
You Can Control Your Weight As You Quit Smoking
Will I Gain Weight if I Quit Smoking?
Weight gain and quitting smoking