Nervous nibbles alone do not explain the weight that people tend to gain when they give up smoking, Swiss researchers said Thursday, turning the spotlight instead on a bacterial shift in the intestines.
Studies have shown that quitting smoking leads to an average weight gain of four to five kilogrammes (nine to 11 pounds) in the first year.
But according to researchers at Zurich University Hospital, former smokers who bulk up may not be eating more than before they kissed their cigarettes goodbye.
Noting that even people who cut back on calorie intake after quitting smoking tend to gain weight, Professor Gerhard Rogler said he and his colleagues had discovered another potential explanation: a change in the composition of the intestinal flora among smokers who kick the habit.
Their study, supported by the Swiss National Science Foundation and published in peer-reviewed scientific journal PLoS One, found that when a person stops smoking, the diversity of bacterial strains in their intestines shifts. It more resembles the gut flora found in people with obesity.
Both recent non-smokers and obese people tend to have more of two bacteria types, Proteobacteria and Bacteroidetes, Rogler told AFP.
These germs are believed to use energy more efficiently and break down otherwise indigestible fibres -- and as a result, more of what the person eats is transformed into fat rather than excreted as waste.
The researchers studied the genetic profile of intestinal bacteria found in faecal samples provided by 20 volunteers over nine weeks.
The participants comprised five non-smokers, five smokers and 10 people who had quit smoking one week after the study began.
Little difference was seen in the bacterial biodiversity among the persistent smokers and non-smokers.
But among those who had just given up smoking, there was a clear shift towards more Proteobacteria and Bacteroidetes, the study showed.
Over the study period, the people who had quit smoking also gained an average of 2.2 kilos (4.8 pounds), even though they insisted that their eating and drinking habits were unchanged.
"Under the same living conditions, they gained weight after the cessation of smoking, and they showed a change in the microbiota," Rogler said.
While researchers have yet to prove a clear connection between the two developments, he pointed out that a number of other studies have also showed a link between intestinal bacteria and weight gain.
On Wednesday, a study published in the journal Nature found that individuals with low bacterial "richness" in their intestines were more prone to obesity and associated diseases such as diabetes, heart and cholesterol problems. Six bacterial species appear to play a key role in promoting this diversity.
Rogler said that more research was needed to answer the many questions that arise from such discoveries.
But he said it was clear we should pay more attention to how the environment influences gut functions.
"Nobody believed the people who stopped smoking and said they weren't eating more but still gained weight. Perhaps we simply should be more willing to believe what people tell us," he said.
Also on HuffPost:
You'll Be Less Anxious
Even though smokers may believe taking a long drag on a cigarette can help to calm nerves, a British study published earlier this year suggests that <em>quitting</em> can actually decrease anxiety more over the long-term. "People who achieve abstinence experience a <a href="http://www.cbc.ca/news/health/story/2013/01/02/smoking-quit-anxiety.html">marked reduction in anxiety</a> whereas those who fail to quit experience a modest increase in the long term," researchers wrote in the British Journal of Psychiatry study, as reported by CBC News. Similarly, a 2010 study in the journal Addiction showed that <a href="http://www.reuters.com/article/2010/06/17/us-smoking-idUSTRE65G0CX20100617">perceived stress decreased</a> for people who quit smoking for a year after hospitalization for heart disease, Reuters reported.
Your Mouth Will Thank You
Quitting the habit could dramatically <a href="http://consumer.healthday.com/Article.asp?AID=661533">decrease your risk of dental problems</a> like cavities and gum disease, and even more dangerous conditions like oral cancer, according to a study from the Centers for Disease Control and Prevention. HealthDay reported that <a href="http://consumer.healthday.com/Article.asp?AID=661533">compared with former smokers</a>, smokers have a 1.5-times higher risk of developing at least three oral health conditions.
Your Sex Life Will Be Better
Here's a bedroom-related reason to quit smoking: studies have suggested a link between smoking and decreased sex drives for both men <em>and</em> women. Studies published in 2008 in the Journal of Sexual Medicine showed that nicotine can affect even <a href="http://www.ncbi.nlm.nih.gov/pubmed/17971108">nonsmoking men's</a> and <a href="http://www.ncbi.nlm.nih.gov/pubmed/18331269">women's sexual arousal</a>. And if that's not enough to convince you, well, there's also <a href="http://healthland.time.com/2011/09/15/guys-quitting-smoking-makes-it-bigger-really/">this</a>.
You'll Save Your Skin
If you want your skin to be at its best, then you're better off quitting cigarettes. WebMD points out that smoking <a href="http://www.webmd.com/smoking-cessation/ss/slideshow-ways-smoking-affects-looks">affects skin tone</a>, promotes sagginess and, of course, causes those wrinkles around the lip area. However, the American Society for Aesthetic Plastic Surgery notes that just a month-and-a-half after <a href="http://www.surgery.org/consumers/plastic-surgery-news-briefs/skin-quit-smoking-1031403">quitting smoking</a>, your skin will already begin to look better.
You'll Have More Locks
If you love your hair, maybe it's time to put the cigarettes down. Research has linked smoking with an increased risk of male pattern baldness. BBC News reported in 2007 on a Archives of Dermatology study, showing even after taking into account other hair-loss risk factors like age and race, <a href="http://news.bbc.co.uk/2/hi/health/5413382.stm">heavy smoking</a> (at least 20 cigarettes daily) raised the risk of baldness. And a 2011 study showed that smoking, stress, drinking and genes were all<a href="http://www.webmd.com/skin-problems-and-treatments/hair-loss/news/20110923/divorce-heavy-drinking-smoking-linked-to-hair-loss"> risk factors for baldness</a>, WebMD reported.
Your Mood Will Improve
Here's a pretty good benefit: Stopping smoking could <a href="http://news.brown.edu/pressreleases/2010/12/smoking">make you a happier person</a>, according to research from Brown University. Researchers there found that smokers were <a href="http://news.brown.edu/pressreleases/2010/12/smoking">never happier</a> than when they were quitting smoking, even if they went back to smoking afterward. According to a <a href="http://news.brown.edu/pressreleases/2010/12/smoking">news release</a>: <blockquote> The most illustrative — and somewhat tragic — subjects were the ones who only quit temporarily. Their moods were clearly brightest at the checkups when they were abstinent. After going back to smoking, their mood darkened, in some cases to higher levels of sadness than before.</blockquote>
You'll Have More Birthdays
Stopping smoking may <a href="http://www.huffingtonpost.com/2012/10/29/women-stop-smoking-live-10-years-longer_n_2011804.html">help women live a decade longer</a> than they would have if they had continued lighting up, according to a 2012 study in The Lancet. Researchers also found that the more the women smoked, the higher their risk of premature death, with even "light" smokers (those who smoked just one to nine cigarettes a day) having a doubled risk of death compared with non-smokers. "If women smoke like men, they die like men -- but, whether they are men or women, smokers who stop before reaching middle age will on average <a href="http://www.eurekalert.org/pub_releases/2012-10/l-soa102312.php">gain about an extra ten years of life</a>," study researcher Professor Sir Richard Peto, of the University of Oxford, said in a statement.
You'll Improve Your Pregnancy Chances
If you're trying to conceive, one of the best things you can do is to quit smoking, research shows. NBC News reported that women smokers have a 60 percent <a href="http://today.msnbc.msn.com/id/16874634/ns/today-today_health/t/trying-conceive-quit-smoking/#.UOr-7onjlU4">higher chance of being infertile</a>, compared with nonsmokers. Smoking is also linked to more spontaneous miscarriages, according to NBC News.
You'll Enjoy Food More
If you <a href="http://abcnews.go.com/Health/Healthday/story?id=8427779#.UOsAFInjlU4">don't like bland food</a>, then don't smoke, research suggests. A small 2009 study of Greek soldiers shows an association between smoking and <a href="http://www.eurekalert.org/pub_releases/2009-08/bc-stf081809.php">"fewer and flatter" taste buds</a>, according to a statement on the research.
Your Colds Won't Be As Bad
Mild cold symptoms could take on a more serious form for smokers, according to a study from Yale University researchers. The findings, published in 2008 in the Journal of Clinical Investigation, showed an <a href="http://news.yale.edu/2008/07/24/study-shows-why-cigarette-smoke-makes-flu-other-viral-infections-worse">overreaction of the immune systems</a> of cigarette smoke-exposed mice when exposed to a virus similar to the flu. "The anti-viral responses in the cigarette smoke exposed mice were not only not defective, but were hyperactive," study researcher Dr. Jack A. Elias, M.D., said in a statement. "These findings suggest that smokers do not get in trouble because they can't clear or<a href="http://news.yale.edu/2008/07/24/study-shows-why-cigarette-smoke-makes-flu-other-viral-infections-worse"> fight off the virus</a>; they get in trouble because they overreact to it."
Quitting Smoking And Money Saving
Eletta Hansen explains some facts about smoking, and discusses how much money will you save if you quit smoking