Smokers who quit have improved metabolism

Last Updated: 2015-03-23

By Lorraine L. Janeczko

NEW YORK (Reuters Health) - When smokers quit, their metabolism improves, new research suggests.

After smokers quit, fat settles first in the abdomen but then moves to the thighs, and hepatic glucose output is lower by 24 weeks. Their carbon monoxide (CO) and/or nicotine metabolites decrease, and they have greater insulin sensitivity and glucose oxidation, the study authors wrote in a poster March 5 at ENDO 2015, the annual meeting of the Endocrine Society, in San Diego.

"The metabolic effects of smoking are clearly complex and still not completely understood, but our findings show that with good supervision, the metabolic benefits of cessation can ultimately outweigh any negative effects (such as weight gain), and therefore should be strongly encouraged in all smokers," wrote lead author Dr. Stanley H. Hsia, from the Department of Internal Medicine of Charles R. Drew University of Medicine and Science in Los Angeles, in email to Reuters Health.

Body weight did not change significantly over time, the authors reported.

"I was almost expecting to see at least some weight gain," Dr. Hsia said. "I also didn't expect to see a transient worsening and then a reversal of central adiposity, or the fact that some changes take more time to manifest, all of which just shows how complex the physiology probably is, and why the clinical effects of smoking cessation can appear so heterogeneous," he wrote.

Dr. Hsia and colleagues evaluated 22 healthy, 1/2-to-2-pack-a-day adult smokers. The mean age was 46, the mean weight was 86.6 kg (190.9 lb), and the mean body mass index (BMI) was 30.9 kg/m2. Nineteen participants completed the two-phase 24-week study.

Before and after phase 1, the researchers recorded the number of cigarettes smoked each day, as well as respiratory quotient, glucose oxidation, total and non-oxidative glucose uptake, hepatic glucose output, free fatty acids, fat distribution, weight, body composition, breath carbon monoxide, and urine nicotine metabolites.

During phase 1, an eight-week smoking cessation program with bupropion and behavioral counseling for all participants, the median number of cigarettes smoked per day dropped from 8.8 to 1.4 (p<0.001).

By week 8, there was a reduction in carbon monoxide and urine metabolite levels, which remained low at 24 weeks. Abdominal fat trended higher but reversed significantly and settled in the thighs over the following 16 weeks.

During the 16-week phase 2, the participants did not receive any bupropion or behavioral therapy. Some abstained from smoking while others resumed.

At week 24, the participants' median number of cigarettes remained low at 1.0 (p<0.001). Their respiratory quotient improved, their hepatic glucose output improved along with their lifestyle changes, their weight change correlated directly with decreased nicotine metabolites, and their reduced carbon monoxide and/or nicotine metabolites correlated with greater uptake and oxidation of carbohydrate substrates.

Principal investigator Dr. Theodore C. Friedman, chair of internal medicine at Charles R. Drew University, told Reuters Health by phone, "I was very surprised. I thought the people would gain a lot of weight and that their diabetes would get worse. Instead, they got better. They didn't gain weight, their insulin resistance was generally unchanged and their fat redistribution seemed better. While early on, fat may have gone to the abdomen, it later redistributed to the thigh, which is more benign."

"I think that now, people stop smoking as part of an overall movement to be healthy. Maybe 20 years ago, people would stop smoking because it was expensive or it smelled bad. Now it's all part of being healthy. We didn't see any changes in diet and exercise because the people had already started that before they came for the study. Their diet, exercise, and healthy living prevents them from gaining the weight back and improves their metabolism," Dr. Friedman said.

"We should urge our patients to stop smoking. Cessation is good for them, they won't gain weight, and their metabolic processes will improve," he added.

Drs. Hsia and Friedman said they would like to conduct smoking-cessation studies in larger and more diverse populations and explore whether their results can be sustained longer, the effects of a medication other than bupropion, and why fat accumulation moves from the abdomen to the thighs.

"This could go in many different directions," Dr. Hsia wrote.

The authors disclosed no conflicts of interest.

SOURCE: http://bit.ly/1ECvyNI

ENDO 2015.