When a person quits smoking, the body’s awe-inspiring ability to heal itself begins immediately; along with this wonder of restoration, though, most ex-smokers complain about the weight they gain. Yet a new study from Switzerland finds that putting on the pounds after quitting the butts is not due to eating more, but rather changes in the bacteria residing in our guts.

Guaranteed Weight Gain?

The number of pounds that people gain after they stop smoking has been both studied and debated: some claim the average is about 6 to 8 lbs. while others say it’s more like 15 to 17 lbs. In either case, mostly everyone who takes this important step toward health will temporarily put on the pounds. Because participants in some studies claimed their total calorie intake in the aftermath of smoking had been stable or even decreased, researchers funded by the Swiss National Science Foundation decided to investigate the exact nature of the added pounds.

Working with a group of 10 participants as well as 10 control subjects (five continuing smokers and five non-smokers), the researchers structured a nine-week observational period into health assessment visits stretching from one week before and eight weeks after the 10 participants quit their habit. During the observational period, repetitive stool samples were collected when participants and control subjects made their visits to the smoking consulting program of the University Hospital of Zurich in Switzerland.

The researchers found that during this period, the 10 participants who quit smoking gained an average of 5 lbs. in body weight (at screening, the average body weight was 158 lbs.). However, the participants, with one exception, had not changed their total average daily calorie intake or even their nutritional composition (carbohydrates, proteins, fat, fiber, and alcohol). In other words, all participants but one basically maintained the same diet after quitting the cigarettes.

Why, then, did they gain weight?

Gut Microbiota

Living in our digestive tract (our stomach and intestines) are trillions of microorganisms — quite literally, a world of bacteria that helps with the important work of digesting food. These intestinal inhabitants (formerly known as 'gut flora' but now called 'gut microbiota') not only influence the strength of our immune system, but also regulate nutrition. Any change in the overall composition of gut microbiota has consequences; in fact, scientists have identified shifts in their population as a contributing factor in various diseases, including inflammatory bowel disease and, as one might suspect, obesity.

What, then, these Swiss researchers found is that profound changes occurred in the intestinal environment of the 10 participants who quit smoking and gained weight (despite continuing the same diet). After they ceased smoking, the microbial diversity in their intestines increased. Additionally, the researchers identified shifts in microbial composition, “with an increase of Firmicutes and Actinobacteria and a lower proportion of Bacteroidetes and Proteobacteria on the phylum level,” the researchers wrote. In effect, this new ecosystem favored efficiency, so that more of what was ingested was broken down, and so more fat was created with less waste.

“Interestingly, these changes appear to occur in a comparable manner both microbiologically and clinically (weight gain) as those induced by transplantation of an ‘obese microbiota’ into lean mice,” the researchers wrote. “This relatively short observational period does not permit conclusions about a long-term alteration.”

Certainly for those who are serious about ending their addiction to cigarettes, the long term is what matters most.

Quit Today

According to the Centers for Disease Control and Prevention, an estimated 43.8 million people, almost one in five of all adults in the U.S. smokes cigarettes. More common among men (about 22 percent smoke) than women (16.5 percent smoke), cigarette smoking is the leading cause of preventable death, accounting for more than 440,000 deaths (also about one in five) each year.

Yet, those who quit experience immediate health benefits as their bodies begin to heal. Within 12 hours, blood oxygen levels will have increased to normal while carbon monoxide levels will have decreased to normal. Senses of smell and taste return quickly, cravings end quickly enough, and soon most quitters simply begin to feel they have more energy. Longer-term benefits include:

  • Coronary heart disease risk is cut by half one year after quitting and is nearly the same as someone who never smoked 15 years after quitting.
  • Stroke risk is reduced to that of a person who never smoked after five to 15 years of not smoking.
  • Risks for developing cancers of the mouth, throat, and esophagus are halved five years after quitting.
  • Chronic obstructive pulmonary disease risk for death is reduced after quitting.
  • Lung cancer risk drops by as much as half 10 years after quitting.

It is important to remember that, for many people, any weight gain that comes with ‘losing the butts’ is temporary and will be lost soon enough.

Source: Biedermann L, Zeitz J, Mwinyi J, et al. Smoking Cessation Induces Profound Changes in the Composition of the Intestinal Microbiota in Humans. PLOS One. 2013.