Scientists Discover Why Smokers Gain Weight When They Quit
August 29, 2013

Scientists Discover Why Smokers Gain Weight When They Quit

Enid Burns for – Your Universe Online

Many smokers don't want to quit because they are afraid of the weight gain that comes with putting out the cigarette. New findings from the Swiss National Science Foundation show that it's not higher calorie intake, but a change in the composition of intestinal flora.

Researchers find that about 80 percent of smokers put on an average of seven kilograms, or about 15 pounds. "Their weight increases even if their calorie intake remains the same or even falls compared to the level before quitting smoking," said a report on the study.

The study was recently published in PLoS One, a peer-reviewed journal covering research from any scientific discipline. Researchers working with Gerhard Rogler of Zurich University Hospital identified the change in the composition of bacterial diversity in the intestine. They found that bacterial strains commonly found in the intestines of obese people are also present in high numbers in people who recently quit smoking.

This new finding was studied by looking at genetic material of intestinal bacteria found in the feces and studied stool samples. Researchers studied samples from 20 study participants over a period of nine weeks, which included four samples per person. The 20-person study group consisted of five non-smokers, five smokers and ten people who quit smoking one week after the study began.

"While the bacterial diversity in the feces of smokers and non-smokers changed a little over time, giving up smoking resulted in the biggest shift in the composition of the microbial inhabitants of the intestines," the research report said. "The Proteobacteria and Bacteroidetes fractions increased at the expense of representatives of the Firmicutes and Actinobacteria phyla. At the same time, the test subjects who had quit smoking gained an average of 2.2 kilos in weight although their eating and drinking habits remained the same."

Earlier research on mice showed similar findings. In that test, scientists transplanted the feces of obese mice into the intestines of normal-weight mice. Normal-weight mice showed an increase of Proteobacteria and Bacteroidetes in the gut flora. Those mice then experienced weight gain as a result. "The new gut flora apparently used the energy contained in the nutrition more efficiently," the report said.

"Rogler and his colleagues assume that the same effect also manifests itself in their test subjects," the report stated. "The composition of the diverse bacteria in the intestinal flora, which changes after giving up smoking, probably provides the body with more energy, resulting in new non-smokers gaining weight."

Researchers in the study did not provide information on how to balance intestinal flora to a more favorable level. A 2012 study published by public health researchers at the University of Buffalo found that eating fruits and vegetables could help smokers quit. The study showed that smokers who ate more fruits and vegetables were three times more likely to stay tobacco-free for at least 30 days. It is possible that some fruits and vegetables have nutrients that can help balance intestinal flora and limit weight gain.