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Intestinal or Gut Bacteria and Obesity: A Possible Connection

Linda Crampton is a writer and teacher with a first-class honors degree in biology. She often writes about the scientific basis of disease.

Yogurt often contains active probiotic bacteria. In the near future, we may be able to eat probiotics in foods or supplements that help to prevent obesity.

Yogurt often contains active probiotic bacteria. In the near future, we may be able to eat probiotics in foods or supplements that help to prevent obesity.

Obesity and Gut Bacteria

Obesity is a complex condition that may have multiple causes. It's becoming frighteningly common in several parts of the world, including North America. The condition increases the risk of serious health problems, including heart disease, strokes, osteoarthritis, type 2 diabetes, and some types of cancer. Obesity can be a serious drain on public health budgets as communities try to treat the problems that it causes.

Scientists have recently discovered that certain gut bacteria may contribute to—or even cause—obesity. Gut bacteria live in our intestine. The majority inhabit our large intestine, or colon (the longest part of the large intestine). Many intestinal bacteria are very helpful to us; some seem to have neutral effects on our lives; and a few are harmful.

The discovery that gut bacteria may affect body weight could have enormous repercussions in the treatment of obesity. In the future, it may be possible to manipulate the gut environment and its living contents to help normalize weight.

The term "gut" usually refers to our small and large intestine, although sometimes the word refers to the entire gastrointestinal or digestive tract.

The term "gut" usually refers to our small and large intestine, although sometimes the word refers to the entire gastrointestinal or digestive tract.

Definition of Obesity

There is a difference between being overweight and being obese. The definition of obesity is usually based on a number called the body mass index, or BMI. This number is derived from a person's height and weight. There are online calculators that enable a person to discover their BMI. A link to one of them is provided in the "References and Resources" section at the end of this article.

For adults, the significance of the BMI number is as follows:

  • less than 18.5 = underweight
  • 18.5 to 24.9 = normal weight
  • 25.0 to 29.9 = overweight
  • 30.0 or higher = obese

The numbers can be a helpful indication of a person's weight category, but this isn't always the case. For example, athletes often have increased muscle mass. This mass will increase their weight and give them a higher BMI than they would normally have. Seniors often lose muscle. This may reduce their weight and BMI, even though they may have an unhealthy amount of fat in their body.

Being obese is not the same as being overweight.

Being obese is not the same as being overweight.

In 2016, more than 1.9 billion adults aged 18 years and older were overweight. Of these over 650 million adults were obese...In 2018, an estimated 40 million children under the age of 5 years were overweight or obese.

— WHO (World Health Organization)

Gut Bacteria and Health

Scientists say that we have about ten times more bacterial cells in our body than human ones. The bacterial cells are smaller than ours. Bacteria live on our skin and in body passages that are connected to the outside world, such as the respiratory tract and the gastrointestinal tract.

Intriguing research is showing that some of our gut bacteria affect our lives in important ways. They make vitamins that we use, including vitamin K, break down some of our food, reduce the amount of feces that we make, and fight harmful bacteria. Some are thought to boost the activity of our immune system, regulate cholesterol metabolism, or reduce inflammation.

The Human Microbiome Project is a major effort to discover and categorize all of the microorganisms that live in and on our bodies in health and in disease. Identifying these bacteria may have great practical importance. This is especially true with respect to gut bacteria, since they seem to be so important in our lives.

Methanobrevibacter and Weight Gain

Researchers at the Cedars-Sinai Medical Center in California have identified one gut microbe that appears to be indirectly related to weight gain. The microbe is named Methanobrevibacter smithii. Despite its name, it belongs to a group of organisms known as the archaea. The members of this group were once considered to be bacteria. They have many similarities to bacteria but also have some important differences.

The researchers examined exhaled air samples from 792 people with respect to the hydrogen and methane content. They found four results:

  • normal levels of each gas
  • a higher concentration of hydrogen than normal
  • a higher concentration of methane than normal
  • a higher concentration of both gases compared to the normal values

The researchers found that people who had a high concentration of both hydrogen and methane in their breath had a significantly higher BMI and a significantly higher percentage of body fat than the other people in the study.

Scientists say that most of the methane made in our gut is produced by Methanobrevibacter smithii. This microbe absorbs hydrogen released by bacteria and then uses the hydrogen to produce methane. Some of the hydrogen and methane enters our bloodstream and is exhaled by our lungs.

An environment with a high hydrogen content is harmful for some gut bacteria. The researchers think that by absorbing hydrogen from the gut environment, Methanobrevibacter is helping bacteria that release hydrogen to survive and to increase in number. These bacteria may then break down more food, giving themselves and us more nutrients. As time passes, our increased absorption of nutrients could lead to weight gain.

The researchers are now performing experiments in which Methanobrevibacter is eliminated from the gut with targeted antibiotics. They hope to discover how the removal of the microbe affects the processing of food in the gut.

Some researchers feel that obesity is not caused simply by poor food choices.

Some researchers feel that obesity is not caused simply by poor food choices.

Methanobrevibacter and Children's Weight

In another research project, a team of scientists in the Netherlands examined the feces of 472 children between the ages of six and ten. They found that a higher concentration of Methanobrevibacter smithii in the feces (and therefore presumably in the gut) was associated with increased weight, a higher BMI score, and being overweight.

The Dutch researchers say that when Methanobrevibacter removes hydrogen, the rate of bacterial fermentation of carbohydrates and polysaccharides increases. The fermentation process produces substances that humans use.

It should be noted that although multiple researchers have found that Methanobrevibacter smithii appears to contribute to weight gain, some have found that it seems to cause weight loss instead. The study of microbe effects on our body is complex. Many processes and interactions take place in the human body, not all of which are understood. In addition, different people may have a different collection of gut bacteria. The experimental conditions and protocol can also affect the results of a research project.

The worldwide prevalence of obesity nearly tripled between 1975 and 2016.

— WHO (World Health Organization)

A Possible Effect of Enterobacter

Scientists at Shanghai Jiao Tong University in China have discovered that another bacterium may affect obesity. They placed a morbidly obese man on a special diet that was designed to change the composition of his gut flora by altering the pH in the environment. The diet consisted of whole grains, non-digestible carbohydrates, probiotics, and traditional Chinese medicines. The man weighed 175 kg (almost 386 lbs) at the start of the diet. He lost 51 kg (about 112 pounds) during the diet, without exercising.

The researchers found that at the start of the diet a member of the genus Enterobacter was the most abundant bacterium in the man's gut. At the end of the diet (which lasted for twenty-three weeks), the bacterium was almost undetectable in his gut.

The scientists wanted to determine if the change in the gut flora arose because the man lost weight or because the removal of Enterobacter was at least partly responsible for his weight loss. They fed Enterobacter from the patient's gut to some mice but not to others. All the mice were given a high-fat diet. The mice that had the patient's bacterium in their gut gained significantly more weight than the mice without the organism, suggesting that the bacterium can cause weight gain.

Bacteria Linked to Inflammation and Obesity

More bacteria than Methanobrevibacter and Enterobacter are suspected to play a role in obesity. In fact, researchers at the University of Maryland School of Medicine have identified twenty-six species of bacteria that they suspect are linked to inflammation, obesity, and metabolic syndrome.

Metabolic syndrome is a collection of factors that increase a person's risk for cardiovascular disease, strokes, and type 2 diabetes. To be diagnosed with metabolic syndrome a person must have at least three of the following conditions:

  • abdominal obesity (a large waistline)
  • high blood pressure
  • high fasting blood sugar (or blood glucose)
  • high blood triglycerides
  • low HDL cholesterol (the good type of cholesterol)

Although they are not part of the criteria for diagnosing metabolic syndrome, a person with the condition often has a high blood level of LDL cholesterol (the bad cholesterol), insulin resistance, and widespread inflammation.

The researchers found that the twenty-six bacteria were common in people who were obese or had signs of metabolic syndrome but were much less abundant in healthy people. More studies are needed to discover whether the bacteria cause obesity or are present as an effect of the obesity.

Abdominal obesity is the most serious type  with respect to health.

Abdominal obesity is the most serious type with respect to health.

Other Bacteria Linked to Obesity

Researchers have discovered that certain types bacteria can cause obesity in mice. Most intestinal bacteria belong to two groups—the Firmicutes and the Bacteroidetes. At least in mice, the Firmicutes are associated with obesity and the Bacteroidetes with weight loss.

Scientists have taken samples of the intestinal microbiome from obese mice and placed them in the intestine of lean mice which have no intestinal bacteria. As a result, the lean mice have developed extra fat deposits. Researchers have also transplanted the gut bacteria from lean mice into mice with no gut bacteria. This causes no change in the weight of the recipient mice. All of the mice in the experiments were given identical food containing the same number of calories.

What is true for mice may not be true for humans, but it often is. To complicate matters, however, researchers have noticed that when obese people lose weight the proportion of Bacteroidetes to Firmicutes in their gut increases. The decrease in weight may have triggered this change.

A Potential Problem With Yo-Yo Diets

The term "yo-yo" diet is used to describe the situation in which a person loses some weight on a diet, returns to their former diet, regains some weight, and then returns to the weight-loss diet in an attempt to remove the weight that has just been gained. Some people follow this pattern repeatedly. Research suggests that there is a special problem with the pattern in terms of gut bacteria.

In 2016, some Israeli scientists reported that mice on a yo-yo diet gained more weight than mice not on a special diet but ingesting the same number of calories over the same time period. In addition, the mice on a yo-yo diet had a less diverse collection of bacteria in their gut. It's often been noticed that obese humans have a lower diversity in their gut bacteria than lean people. When intestinal bacteria from the yo-yo dieters were transplanted into mice that were not on a special diet, the animals experienced an additional weight gain beyond what would be expected from their food intake.

Foods rich in fibre, such as breads made from whole grains, have been linked to weight loss.

Foods rich in fibre, such as breads made from whole grains, have been linked to weight loss.

Genes, Diet, Gut Diversity, and Weight Loss

In 2017, researchers at the University of Nottingham published an interesting report in the International Journal of Obesity. The research team studied 1,632 women (but no men, which may have been a limitation of the study). All of the women had a twin involved in the project. In about half of the cases, the twin was an identical one. The fact that identical twins are genetically identical enabled the researchers to discover the role of genes in weight determination.

After nine years, the researchers found that the women who had a diet that was rich in fibre were less likely to have gained weight than other women, even if the other woman in the comparison was an identical or non-identical twin and had eaten roughly the same number of calories. In fact, they found that genetics was responsible for less then than half of an observed weight change. In addition, the researchers found that woman who had maintained the same weight over the nine-year period or who had lost weight had a more diverse collection of gut bacteria.

Diet can affect both weight and gut bacteria. The researchers acknowledge that they have only shown a correlation between the composition of the gut microbiome and weight and haven't actually proven that gut bacteria can affect people's weight. They point out that studies in mice support this idea, however. It's interesting that some of the unique bacteria in the lean women in the experiment have been found to contribute to weight loss or maintenance in mice. Transferring gut bacteria from one person to another is not considered appropriate (except in very special health situations and with special precautions), so we can't confirm the role of the "lean" bacteria in humans as has been done in mice.

Antibiotics and the Gut Microbiome

More evidence supporting the link between weight and the gut microbiome comes from the use of antibiotics. Using broad-spectrum antibiotics (those that kill multiple species of bacteria) either repeatedly or continuously can reduce gut bacteria diversity. This change can be accompanied by weight gain.

Some relevant and interesting discoveries have been reported in Berkeley Wellness, an online publication of the University of California, Berkeley. Links to the original research articles are given in the report, which is referenced below.

  • A study published in a 2015 edition of the Nature journal described an analysis of 2010 national prescription information. The researchers found that by the time an average child in their sample had reached the age of two, he or she had received "close to three" courses of antibiotics. By the age of ten, an average child had received ten courses of antibiotics.
  • A study published in 2014 in JAMA Pediatrics examined the health records of 64,000 children in Philadelphia. The children who had been treated by antibiotics at least four times by the time they were two years old had a greater risk of becoming obese by the age of five. The relationship was strongest if broad-spectrum antibiotics were prescribed.
  • A study published in the International Journal of Obesity in 2014 followed 400 pregnant women as well as their offspring up to the age of seven. The researchers found that the women who had taken an antibiotic in the second or third trimester of pregnancy had a significantly higher chance of having an obese child.

It's important that a child or an adult takes a prescribed antibiotic. The medication can save lives. It would be best if a doctor could prescribe a narrow-spectrum antibiotic whenever possible, however. This kills targeted bacteria instead of the general bacteria population. It would also be good if antibiotics of any type were prescribed only when necessary.

Waists are expanding in many parts of the world. It's important that we find an effective solution for this problem.

Waists are expanding in many parts of the world. It's important that we find an effective solution for this problem.

Causes and Potential Treatments of Obesity

While inappropriate food choices and lack of exercise can cause weight gain, there is a growing suspicion that the causes of obesity are more complex. Some researchers believe that obesity is caused or influenced by fundamental changes in the body. One of these changes may be the composition of the intestinal microbiome.

There are two possible reasons for the observed link between gut bacteria and obesity. Specific gut bacteria could be the cause of obesity. On the other hand, obesity may produce conditions that favour the presence of the bacteria. Research results obtained so far suggest that in at least some cases the presence of specific bacteria contributes to obesity. This is an exciting observation because it could open the door to new treatments for the condition.

Certain bacteria may be able to prevent obesity by destroying harmful bacteria or by keeping their population under control. Other bacteria may change the environment in the gut, making conditions unfavourable for the growth of the harmful bacteria.

"Probiotics" are bacteria and yeasts that are thought to have health benefits. In the future, it may to possible to give people obesity-fighting bacteria in the form of a probiotic supplement. Dietary components may also be used to change the gut environment in a helpful way. Another possibility is that targeted antibiotics may be able to destroy harmful bacteria. Research is ongoing.

A Healthy Diet and a Good Exercise Routine

It's well known that a bad diet and lack of exercise often lead to weight gain. Anybody who is overweight or obese should modify their diet and exercise routine if these need improvement. It would be wonderful if the addition of certain bacteria to the intestine could help the process of weight loss, though. In the near future we will hopefully have new ways to help obese people. Obesity is a problem that we need to solve.

References and Resources

  • An NHLBI online BMI calculator (If you enter your height and weight into this National Heart, Lung, and Blood Institute calculator, your BMI will be quickly displayed.)
  • Obesity and overweight fact sheet from the World Health Organization
  • Microorganisms detected via breath test linked to body mass, fat accumulation from the EurekAlert news service
  • Gut colonization with Methanobrevibacter smithii is associated with childhood weight development from the Obesity journal, Wiley Online Library
  • Enterobacter and weight gain from New Scientist
  • Gut bacteria linked to obesity and metabolic syndrome identified from the Medical Xpress news service
  • Bacteria and obesity in mice from the NIH (National Institutes of Health)
  • Yo-Yo dieting and gut bacteria play a role in long-term weight gain from an associate professor at the University of Nottingham via The Conversation
  • Antibiotics, obesity, and the gut microbiome from the University of California, Berkeley, via Berkeley Wellness
  • Information about the Human Microbiome Project from the NIH

This content is accurate and true to the best of the author’s knowledge and does not substitute for diagnosis, prognosis, treatment, prescription, and/or dietary advice from a licensed health professional. Drugs, supplements, and natural remedies may have dangerous side effects. If pregnant or nursing, consult with a qualified provider on an individual basis. Seek immediate help if you are experiencing a medical emergency.

© 2013 Linda Crampton

Comments

Linda Crampton (author) from British Columbia, Canada on May 05, 2013:

Thank you so much, Sue! I appreciate all your comments very much!

Susan Bailey from South Yorkshire, UK on May 05, 2013:

Another great hub! I'm in danger of becoming your number one fan.

Linda Crampton (author) from British Columbia, Canada on April 22, 2013:

Thank you, Ingenira. I'm glad that the article was more interesting than an encyclopedia article!

Ingenira on April 22, 2013:

I think I am reading the encyclopedia ! But you made it more interesting. :)

Linda Crampton (author) from British Columbia, Canada on April 11, 2013:

Thank you so much, Linda. I appreciate your comment and all the votes. Yes, it would be wonderful if the research with gut bacteria helps to end obesity. It's such a serious disorder.

Linda Rogers from Minnesota on April 11, 2013:

You did an excellent job researching this topic Alicia. Wouldn't it be wonderful if this research ends in helping obesity. I hit many buttons and voted up on this important hub.

Linda Crampton (author) from British Columbia, Canada on April 04, 2013:

Thank you very much for the comment and all the votes, Peggy. It's interesting to think about all the possible causes of obesity. It's a complex condition.

Peggy Woods from Houston, Texas on April 04, 2013:

This is very interesting research Alicia. I hope that they come up with some definitive results in order to properly combat the obesity epidemic. Since the proliferation of antibiotics in foods we eat and over treatment with antibiotics, it makes one wonder if that is a part of the causative factors causing so much obesity today. Naturally there are other causes as well...but good that research is being done in this area. Up, useful and interesting votes.

Linda Crampton (author) from British Columbia, Canada on March 31, 2013:

Thank you for the comment, Rebecca. The discoveries made by nutrition scientists certainly are interesting!

Rebecca Mealey from Northeastern Georgia, USA on March 31, 2013:

Very interesting. I love the way food and nutrition science keeps coming up with new stuff. I haven't heard this theory until now. Thanks for sharing!

Linda Crampton (author) from British Columbia, Canada on March 29, 2013:

Thank you for the comment, Dianna. It's very sad that obesity is such a major problem today.

Dianna Mendez on March 29, 2013:

I can see this truth in our present society. So many people out there are suffering from this. Great hub post, Alicia.

Linda Crampton (author) from British Columbia, Canada on March 29, 2013:

Thank you very much for the comment, Nettlemere. I appreciate it! The human microbiome project is ambitious, but I think it's very interesting.

Nettlemere from Burnley, Lancashire, UK on March 29, 2013:

Amazing how much there is left to learn about us! I hadn't heard of the human microbiome project. Lots of interesting facts in this well written and researched article!

Linda Crampton (author) from British Columbia, Canada on March 29, 2013:

Thank you, Eddy. Have a good weekend!

Eiddwen from Wales on March 29, 2013:

So interesting and very useful Alicia;will benfit many so thank you for sharing.

Eddy.

Linda Crampton (author) from British Columbia, Canada on March 28, 2013:

Thanks for the visit and for sharing the information, Deb. I hope that influencing the gut bacteria will make people healthier.

Deb Hirt from Stillwater, OK on March 28, 2013:

If this works out, people will become significantly healthier. I like the idea. I have found that since eliminating meat from my diet, for the most part, I have lost weight and kept it off, too.

Linda Crampton (author) from British Columbia, Canada on March 28, 2013:

Thank you very much, Bill. I appreciate the comment as well as the vote and the share! Some researchers do say that while it's important to remove harmful germs from our skin after high-risks activities, such as using a restroom, some of us are using too many antibacterial substances.

Bill De Giulio from Massachusetts on March 28, 2013:

Fascinating article Alicia. Also a little spooky knowing that we have more bacteria cells than human cells in our bodies. But I suppose they serve a function. I am lucky in that I have never had a weight problem! That doesn't mean I won't in the future. I also wonder how the use of antibacterial soaps, lotions, etc. affects all of this. You clearly researched this very well, great job. Voting up and sharing.

Linda Crampton (author) from British Columbia, Canada on March 28, 2013:

Hi, watergeek. You've raised some very interesting points. Whatever the cause or causes, the obesity problem, or the "obesity epidemic" as some people call it, needs to be solved. Thanks for the visit.

Susette Horspool from Pasadena CA on March 28, 2013:

We're constantly looking for ways to blame weight on anything except our own good diet and exercise. Are they looking at all at the connection between constipation and weight gain? Or individuals misreading body signals and eating instead of drinking water? I wonder if that bacterium's job is to compensate, somehow, for the lack of water in the gut, which causes constipation, which causes a buildup of bacteria in the colon. Methanobrevibactor could be an indicator specie, rather than a cause, per se.

Linda Crampton (author) from British Columbia, Canada on March 28, 2013:

Thanks for the comment, b. Malin. Yes, a good diet and regular exercise are very important for maintaining a healthy weight! Some people may need extra help, though, which is why I hope the gut bacteria research is successful.

b. Malin on March 28, 2013:

Hi Alicia, I'm always Amazed at what I learn from your Hubs...Gut Bacteria, who knew? Of course bottom line, in our Country People do eat too much and DON'T exercise.

Probiotics, could that be the answer, along with a Healthy Diet and Exercise. Anyway, thanks for Educating and sharing.

Linda Crampton (author) from British Columbia, Canada on March 28, 2013:

Thank you, thebiologyofleah. I hope that gut bacteria are part of the solution. The obesity problem needs to be solved!

Leah Kennedy-Jangraw from Massachusetts on March 28, 2013:

Really nice summary of all the research going on in this field of study-thanks for sharing. It makes sense that something as multifactoral as obesity should be treated in a multitude of ways. Looks like this angle may be part of the solution.

Linda Crampton (author) from British Columbia, Canada on March 28, 2013:

Hi, osaeoppongde. Thanks for the comment and for sharing the interesting information!

Deborah L. Osae-Oppong from Chicago, IL on March 28, 2013:

This is great! The gut microbiome is definitely connected to our health and immune system, thanks for the info! I read the other day that there is also a link between circadian rhythm, gut bacteria, and overall health.

Linda Crampton (author) from British Columbia, Canada on March 27, 2013:

Thank you very much for such a nice comment and for the vote and tweet, wqaindia! I appreciate your visit. There may be several causes of obesity. It's an interesting and important topic to investigate!

Ashok Goyal from 448 Dalima Vihar Rajpura 140401 Punjab India on March 27, 2013:

You have touched a burning topic and that too with a lot of useful information. Every possible cause of obesity is taken care of. Let the preventive steps and causes are circulated to bigger audience. Voted up and tweeted..

Linda Crampton (author) from British Columbia, Canada on March 27, 2013:

Thank you very much for the vote and the share, LA Elsen! I'm sure that there's a lot more for us to discover about the causes of obesity. It's a complicated disorder.

LA Elsen from Chicago, IL on March 27, 2013:

Very interesting and informative. I have no doubt in my mind that there are other factors causing the obesity epidemic. Very enlightening.

Voted up and shared.

Linda Crampton (author) from British Columbia, Canada on March 27, 2013:

Thanks for the visit and the comment, drbj. It would be wonderful if scientists could safely influence the bacterial community in the gut to cure obesity. I hope this wish becomes reality!

Linda Crampton (author) from British Columbia, Canada on March 27, 2013:

Hi, wabash annie. Yes, sometimes obese people are stigmatized for their condition when they aren't doing anything obvious to cause their problem. Even if they are following an unhealthy lifestyle they need help instead of criticism. Thanks for the comment.

Linda Crampton (author) from British Columbia, Canada on March 27, 2013:

Hi, cabmgmnt. Yes, antibiotic treatment can be very frustrating when it kills good bacteria as well as the bad ones! An interesting development is the appearance of narrow spectrum or targeted antibiotics that kill only certain bacteria. I hope these become more effective at destroying specific bacteria and leaving others unharmed. We certainly need better antibiotics! Thanks for the comment.

drbj and sherry from south Florida on March 27, 2013:

This is a fascinating subject, Alicia, as our country is becoming obesogenic. I, too, wrote about this subject in my hub, 'Obesity is Widespread.' What a boon to mankind if scientists can discover how to helpfully change our gut bacteria to combat weight gain.

wabash annie from Colorado Front Range on March 27, 2013:

Most of us have wondered about what has been causing the obesity 'epidemic'. Often extremely overweight people eat no more/worse than anyone else. Your information is very interesting.

Corey from Northfield, MA on March 27, 2013:

interesting insights, sad to say that antibiotics wipe out good flora in your intestines making the use of probiotics almost necessary for optimal gut health.

Linda Crampton (author) from British Columbia, Canada on March 27, 2013:

Thank you very much for the visit and the comment, Bill. It is scary to see that obesity is becoming more common in so many areas. I hope new solutions are found very soon.

Bill Holland from Olympia, WA on March 27, 2013:

Great information, Alicia. Happily I have never had a problem with obesity but this country certainly does. Very interesting facts.