Why Do You Gain Weight After You Quit Smoking?

Why Do You Gain Weight After You Quit Smoking?

Researchers have noticed that after stopping smoking, the intestinal flora underwent strong changes. This could be at the origin of the weight gain often experienced by those who quit smoking. On average, 80% of people who quit smoking take 15 pounds in the following months. A phenomenon that is attributed regularly to a greater food intake: we eat more so we grow. But, some studies have shown that the weight of smokers tends to increase even if their diet does not change.

Why Do You Gain Weight After You Quit Smoking

Today, the researchers at the University Hospital in Zurich think they have found a way to explain such a consequence: this weight gain could be due to a change in the intestinal bacterial flora. In their study published in the on-line journal PLoS ONE, the researchers analyzed the tracks of bacterial genetic material in the feces of 20 people: 5 non-smokers, 5 smokers and 10 who stopped smoking one week after the beginning of study. Volunteers were followed for 9 weeks. The intestinal bacteria (also called “flora” or “microbiota”) are mutual organizations meaning that the cooperation between them and us is mutually beneficial. There are an average of 500 species of bacteria (totaling several billion bacteria) in the human intestines, which help us digest food, especially plant tissue.

A Notable Change In Bacterial Species

After the nine weeks, the researchers compiled the results and compared them for each group of individuals. In smokers and non-smokers, the bacterial composition changed little during the study. But, in the people who stopped, an important change occurred: the distribution of species was no longer the same. Some bacteria were more numerous while others were less so. According to the researchers, the observed distribution finally resembled that found in obese people.

On average, people who stopped smoking gained 4.85 pound, without changing their eating habits, over the course of nine weeks. In their work, researchers believe that this change in the intestinal flora could be responsible for the observed weight gain. In addition, they also noted that by the end of the study, former smokers consumed slightly more alcohol than before they quit smoking.

Improved Energy Efficiency

For Gerahrd Rogler, author of the study, these results should be compared with a previous study in mice. By transferring the intestinal flora of obese mice to normal mice, the latter had gained weight. The new intestinal flora had been able to better digest the food, for better energy efficiency, and thus caused weight gain.

Thus, the researchers believe that the same mechanism would be at work after quitting smoking: by changing, the intestinal flora would better convert food into energy, which would ultimately result in weight gain. This study is published only a few days after another conducted by INRA researchers and which seems to confirm the role played by the intestinal flora in overweight and obesity.

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