Researchers of a new study found that changes in the composition of intestinal flora leads to smokers gaining weight after they quit smoking.

It is often found that when a smoker quits cigarettes, he or she automatically gains a few extra pounds. Researchers of a new study found that this has nothing to do with consuming extra calories but because of changes in the composition intestinal flora.

Eight percent of smokers who quit put on an average of seven extra kilos. For the study, Gerhard Rogler of Zurich University Hospital examined the genetic material of intestinal bacteria found in stool samples, which they had received from twenty different persons over a period of nine weeks. The test persons included five non-smokers, five smokers and ten persons who had quit smoking one week after the start of the study.

Researchers found that the bacterial diversity changed only a little over time in smokers and non-smokers. However, there was a big shift in the composition of the microbial inhabitants of the intestines among smokers who had quit. Researchers also found that such people gained an average of 2.2 kilos in weight although their eating and drinking habits remained the same.

The results of this new study were similar to a previous study that transplanted the faeces of obese mice into the intestines of normal-weight mice. In that study a similar increase in the fractions of the Proteobacteria and Bacteroidetes in the gut flora was observed.