You better know your Smithiis from your Bacteroidetes and Firmicutes or you might start gaining weight. I guess this statement will require quite a lot of explanation. Can I just assume that you know that you carry a lot of microorganisms in your gastrointestinal system? As a matter of fact the number of microbes easily outnumber your own cells. It is believed that the gut microflora contains somewhere around one million million cells (trillion if you are American or billion if you are continental European, confusing I know but big numbers anyway) and weighs between 1 to 2 kilograms. It consists of around 500 different types of microorganisms, many we have not been able to grow outside the gut.
Just so you know, we are born with a sterile gut but very quickly pick up the crucial microorganisms. Within days bugs have colonised the colon in particular with the initial composition dependent on the birth method and food delivery method (natural birth or cesarian section, breast or bottle to be precise).
Why do we carry so many bugs?
The fact that we quickly colonise the colon with beneficial bugs is very important. We actually will live in a symbiotic relationship with our friendly bugs, that is we are mutually beneficial to each other. Our friends fulfil a host of useful functions, including digestion of left-over energy in food, stimulating cell growth, hindering the growth of harmful microorganisms, training the immune system to respond only to disease causing bacteria, and defending against some diseases. Without gut microflora, the human body would be unable to use some of the undigested carbohydrates we consume. However, because some types of gut flora have enzymes that human cells lack they can break down left-over polysaccharides. These include certain starches, fibre, oligosaccharides and sugars that the body failed to digest and absorb.
The bacteria ferment the left-over carbohydrates into short chain fatty acids including acetic acid, propionic acid and butyric acid. These materials provide a major source of useful energy and nutrients for humans. The bugs also help the body to absorb essential dietary minerals such as calcium, magnesium and iron. Evidence also indicates that bacteria enhance the absorption and storage of lipids and produce and then facilitate absorption of necessary vitamins like vitamin K.
This is all good to an extent, because we don’t want to waste food. And we would without the gut microflora. It has been shown in laboratory experiments that animals raised in a sterile environment and lacking gut flora need to eat 30% more calories just to remain the same weight as their normal counterparts. Unfortunately, the gut flora is in a constant state of change and the important balance between microbes can be disturbed. An excess of some of the bugs can make digestion too efficient, and in here lies the problem.
The problem bug
In 2009, a large human study concerning obesity and gut flora was conducted. It was found that obesity disorders could be the result of an imbalance in the gut flora, which could have serious consequences such as cardiovascular disease, type-2 diabetes, and colon cancer. However, a recent study by a different group took the science one step further finding that overweight people may be more likely to harbour a certain type of intestinal microbe. This microbe may contribute to weight gain by helping other organisms to digest certain nutrients, making even more calories available.
The dark force that seems to cause weight gain is called Methanobrevibacter smithii (the Smithii from the initial sentence). The more M. smithii bugs you have, the more you are likely to weigh. As is implied by the name of the organism it produces methane when digesting food. A way of detecting the presence of the organism is to test the amount of methane and hydrogen in the breath – elevated levels indicate the presence of the bug. The scientists found that people with the highest readings on the breath test were more likely to be heavier and have more body fat, and they suspect that M. smithii may be at least partly responsible for their obesity.
This type of organism may have been useful thousands of years ago, when people ate more roughage and needed all the help they could get to squeeze every last calorie out of their food. But modern diets are much richer and the need less. It thus seems that our external environment is changing faster than our internal environment can cope.
As a curiosity M. smithii was also found in higher numbers in anorexic patients. On the surface this seems to be an anomaly. However, it is believed that this may be due to an adaptive attempt by the gut microflora towards optimal use of the low caloric diet of anorexic patients.
A possible future solution
Question is should we just accept our fate and let the bugs grow as they want? Maybe not since scientists are trying to figure out if it would be possible to help people lose weight by selectively killing off the guilty bug. They are fully aware that to just kill gut bacteria in general could be a disaster. Studies have already shown that taking antibiotics can alter the balance of microbes in a bad way, causing stomach upset, possibly allowing deadly infections to take hold and, perhaps, even allowing a takeover by the obesity-generating bugs. However, a future selective pill targeting our Smithii might be a possibility for losing weight.
- Doctors Detect Obesity Bug on Breath (livescience.com)
- Study Links Obesity to Gut Microflora (sci-news.com)
- Obesity May Be Linked To Microorganisms Living In The Gut (medicalnewstoday.com)
- Breath Test Reveals Gut Bacteria Linked To Obesity (medicalnewstoday.com)
- Obesity may be linked to microorganisms living in the gut (scienceblog.com)
- A breath test might show it’s not your fault you’re fat (bodyodd.nbcnews.com)
- M. Smithii Breath Test Linked to Human Fat Accumulation (sciencespacerobots.com)