Intestinal or Gut Bacteria and Obesity: A Possible Connection
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.
In 2014, more than 1.9 billion adults, 18 years and older, were overweight. Of these over 600 million were obese.— WHO (World Health Organization)
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. The BMI is derived from a person's height and weight. There are online calculators which enable a person to discover their BMI. A link to one of them is provided in the "References and Useful Links" 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.
Worldwide obesity has more than doubled since 1980.— WHO (World Health Organization)
Gut Bacteria and Health
Scientists say that we have about ten times more bacterial cells in our body than human cells. 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.
The Human Microbiome
Bacteria in the Intestine and Weight Gain
Researchers at the Cedars-Sinai Medical Center in California have identified one bacterium that appears to be related to weight gain.
The scientists examined exhaled air samples from 792 people. They found that people who had a high concentration of both methane and hydrogen in their breath had a significantly higher BMI and a significantly higher percentage of body fat than other people. The other people who were tested either had normal breath or exhaled a high concentration of only one of the gases.
Scientists know that most of the methane made in our gut is produced by a bacterium called Methanobrevibacter smithii. This bacterium is known to absorb hydrogen made by other bacteria and then use the hydrogen to produce methane. The researchers suggest—but don't yet know—that by taking hydrogen from other bacteria Methanobrevibacter is helping these bacteria to survive better. These other 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 bacterium affects the processing of food in the gut.
42 million children under the age of 5 were overweight or obese in 2013.— WHO (World Health Organization)
A Possible Role of Enterobacter in Weight Gain
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 gut pH. 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 and Metabolic Syndrome
Gut Bacteria Linked to Obesity and Metabolic Syndrome
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.
Other Bacteria Linked to Obesity
Researchers have discovered that certain bacteria can cause obesity in mice. A group of bacteria called the Firmicutes is associated with obesity and a group known as the Bacteroidetes is associated with weight loss.
Scientists took samples of the intestinal microbiome from obese mice and placed them in the intestine of lean mice. As a result, the lean mice developed extra fat deposits. What is true for mice may not be true for humans, but it often is.
Despite the suspicion that gut bacteria contribute to obesity, the conventional suggestions for losing weight are still important. These include limiting fat and sugar in the diet, including whole grains, vegetables, legumes (pulses), and unsweetened fruits, and exercising for at least 150 minutes a week. Obese and very overweight people should always seek medical advice before starting an exercise program.
What Are Probiotics?
The 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 antibiotics may be able to destroy harmful bacteria. Research is ongoing.
A Healthy Diet and a Good Exercise Routine Are Important
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 Useful Links
Just enter your height and weight into this handy National Heart, Lung, and Blood Institute calculator and it will quickly display your BMI.
- Endocrine Society. (2013, March 26). Microorganisms detected via breath test linked to body mass, fat accumulation. ScienceDaily. Retrieved July 23, 2017 from www.sciencedaily.com/releases/2013/03/130326095056.htm
- Enterobacter and Weight Gain from New Scientist
- University of Maryland Medical Center. (2012, August 15). Gut bacteria linked to obesity and metabolic syndrome identified. ScienceDaily. Retrieved July 24, 2017 from www.sciencedaily.com/releases/2012/08/120815174902.htm
- Bacteria and Obesity in Mice from the NIH (National Institutes of Health)
- The Human Microbiome Project is run by the NIH.
© 2013 Linda Crampton