There is a lot of interest and excitement in the research going on about the microscopic organisms that reside in our intestines (called ‘gut microbiota’). And so there should be! Did you know that human beings are not actually 100% human, but that we are actually made up of 90% gut microbiota cells and only 10% human cells? Mind boggling, isn’t it.
It turns out that we have evolved to welcome gut microbiota into our own personal ecosystems, such that these bugs actually do some work for us behind the scenes. For example, while simple and complex polysaccharides (ie, dietary fiber) escape digestion by our upper gastrointestinal (GI) tracts, they can be transformed by bacteria into digestible substances such as sugars or short chain fatty acids. These short chain fatty acids are involved in regulation of fat storage in the liver and throughout the body via numerous mechanisms that we are only just beginning to understand.
The type of gut bugs we carry is important, but the story is far from clear. In studies of rodents, obesity seems to be associated with carrying more of the Firmicutes phylum and less of the Bacteroides phylum, but the research is quite conflicted on this when it comes to humans. If there is a relationship between the type of bacteria and obesity, it’s unclear which is the chicken and which is the egg – in other words, did these bacteria contribute to obesity, or does developing obesity (or eating a poor diet, thus increasing the risk of obesity) change the gut bacteria towards this particular balance?
The gut microbiota also appear to play a role in the production of gut hormones (such as GLP-1) that signal our brains that we are feeling full during a meal, and this response differs depending on what type of bacteria we carry. Certain types of gut bugs may also stimulate production of inflammatory chemicals by our immune systems that contribute to the risk of insulin resistance, type 2 diabetes, metabolic syndrome, and so forth.
There are probably more unanswered questions than answered ones at this point in the area of the gut microbiome and how it plays into obesity, and thankfully, there is a lot of research ongoing in this area. A growing body of evidence supports the possibility of prebiotic or probiotic approaches to changing the composition of the gut microbiota in favor of certain types of gut bugs, thereby having a positive impact on obesity and related diseases. I will be following this area with interest!