SAN DIEGO — Individuals who quit smoking appear to have improved metabolic effects, according to a new study presented at ENDO 2015. 

Many individuals worry that when they stop smoking, they are going to gain weight and their diabetes and insulin resistance are going to worsen. However, California researchers have reported that this theory may just be a myth and that insulin resistance is basically the same after quitting smoking. In addition, fat redistribution appeared to improve over time in the study.

“We did this study because smoking and smoking cessation have been associated with having diabetes and metabolic syndrome. Smoking cessation has been associated with weight gain,” said principal investigator Theodore Friedman, MS, MD, PhD, who is chair of the Department of Internal Medicine of Charles R. Drew University of Medicine and Science in Los Angeles. 

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“We found that when [study participants] stopped smoking, they didn’t gain any weight. The weight shifted at first, and it went into the abdomen in the very beginning, which is detrimental. But then it went into the thighs, which is good for them. Also the amount of glucose, which is made in the liver, went down, which also helps protect them against diabetes.”

In this study, researchers enrolled healthy, half-to-2 pack-per-day smokers into an 8-week smoking cessation program of behavioral counseling plus oral bupropion (phase 1), followed by a 16-week maintenance period without counseling or bupropion. 

During the 16 weeks, individuals either continued abstaining from smoking or naturally resumed/increased smoking (phase 2). The study included 22 individuals before and after phase 1 and 19 individuals continued through phase 2. 

The researchers prospectively studied metabolic changes using hyperinsulinemic euglycemic clamps coupled with stable isotope tracers to measure hepatic glucose output (HGO) and indirect calorimetry to measure substrate utilization.

Before and after phase 1, the researchers measured the subjects’ number of cigarettes per day, breath carbon monoxide, urine nicotine metabolites, weight, body composition, fat distribution, free fatty acids, and rate of glucose release from the liver and overall glucose utilization. 

Dr. Friedman reported at this meeting that smoking cessation over 8 weeks was associated with a slight and transient worsening of central fat distribution, followed by a larger, favorable reversal over subsequent months. 

Over 24 weeks, hepatic glucose output improved in relation to lifestyle changes. In addition, weight change correlated directly with reduced nicotine metabolites, and reduced carbon monoxide and/or nicotine metabolites correlated with increased glucose uptake and utilization of carbohydrate substrates as the preferred metabolic fuel.

The exact metabolic changes occurring with smoking or smoking cessation until now have not been well studied, and this has been an area of controversy. This current study addresses a knowledge gap and it appears to have significant clinical implications.

Dr. Friedman said smoking cessation appears to have complex but generally favorable metabolic effects, and all smokers should be encouraged to quit. 

“Basically, the bottom line is that smoking cessation is really favorable, and it doesn’t give you more regional obesity and diabetes. It gives you less risk and that is important for endocrinologists to know and to share with their patients,” Dr. Friedman told Endocrinology Advisor


  1. Friedman T et al. Abstract THR-622. Presented at: The Endocrine Society’s 97th Annual Meeting & Expo (ENDO 2015); March 5-8, 2015; San Diego.