Effect of Nicotine

Nicotine from cigarette smoking stimulates the central nervous system, increasing heart rate and the body's metabolic rate, which helps burn calories.

Effect of Quitting

According to smokefree.gov, the Tobacco Research and Intervention Program at the University of South Florida has shown smoking cessation returns the body's metabolism to normal levels. The more cigarettes smoked per day, the greater the decrease in metabolism after cessation. The average smoker gains 4 to 10 pounds after quitting.

Contrary Evidence

According to a study in the "Journal of Applied Psychology" cited by vanderbilt.edu, smokers and nonsmokers have very similar resting metabolic rates, and this rate declines very little after quitting. In and of itself, not using nicotine shouldn't lead to drastic weight gain, but behavioral factors may.

Time Frame

According smokefree.gov, the Tobacco Research and Intervention Program at the University of South Florida has shown it can take up to six months for metabolism levels to return to normal after a smoker quits. Levels often slow to below normal before returning to the presmoking level.

Expert Insight

Edward C. Rosenow III, M.D, an emeritus internist at the Mayo Clinic, suggests those who quit smoking should exercise and maintain a healthy diet to combat the decrease in metabolism.

Source:

Vanderbilt University: Nicotine as a Means for Weight Control

PubMed: Metabolic Effects of Cigarette Smoking

Mayo Clinic: Quit Smoking

Resource:

American Cancer Society: Guide to Quitting Smoking

Smokefree.gov: Forever Free!