Scientific Nutrition Update 17: Dietary Fiber, Gut Bacteria, Short Chain Fatty Acids, and Type 2 Diabetes

Today’s episode was fun because in order to record this I had to learn a whole bunch of new material to understand it.  I love when that happens, because it shows me that even when I have been in a field like this for a while I can still learn new things like about short chain fatty acids.


For today’s episode we are going to talk about a brand new study that posits an interesting connection between dietary fiber, your gut microbiome, and type 2 diabetes.  Just a warning before I get started, this is going to be somewhat heavier science than I normally get into. There was a really interesting study published in Science very recently called “Gut bacteria selectively promoted by dietary fibers alleviate type 2 diabetes” which suggested some interesting links between fiber consumption, gut microbiota, and type 2 diabetes.  Also another hat tip to Dr. Matthew Dalby for introducing me to this article.


First things first we need to clarify why the gut microbiome is so important to us here.  There has been increasingly a push towards a more complete understanding of human health, that includes genetically distinct cells such as the ones that exist in our digestive system for a more complete understanding of the factors that affect our overall health.  There have even been studies that have suggested the composition of our gut microbiome may be linked to obesity, though before I continue I do want to say that there are problems with many of those studies, especially in terms of how they draw the causal arrow. Now you may be wondering how we are going to connect these bacteria in our gut to a disease like type 2 diabetes, and that is through some interesting compounds called: short chain fatty acids.


Now short chain fatty acids are exactly what they sound like, they are fatty acids, that are much shorter than normal.  Specifically they have less than 6 carbons, which is different than other fatty acids which can have 3 dozen. Now the reason we care about these short chain fatty acids is that there production has been associated with a decrease in inflammatory disorders such as Type 2 diabetes.  These short chain fatty acids are part of a mutually beneficial relationship between us and our gut bacteria. We provide them with fiber that is indigestible for us and they provide us with these short chain fatty acids, which provide these anti-inflammatory effects which seem to be helpful in Type 2 diabetes, along with inflammatory bowel disorders such as irritable bowel and Crohn’s disease.  They have even been indicated as helping reduce incidence of diarrhea. Obviously these compounds seem interesting and potentially quite useful.


There seemed to be for these groups that had a high fiber diet, a reduction in fasting glucose, which would seem to indicate better blood sugar control.  Besides that there was also a significant reduction in Hb1AC levels. Hb1AC levels for those who don’t know are one of the most important biomarkers for diabetes, which is a way to basically show the three month average plasma glucose concentration.  Because it gives us a longer term view, it can be a more useful judge than fasting glucose levels. In one of the specific intervention groups here over 80% of the subjects reduced their level below 7% indicating adequate glycemic control.


There has for a long time been a link between fiber consumption and lower incidence of type 2 diabetes, and after reading this study my intuition is that the most likely mechanism for this action is based upon this fermentation of fiber into short chain fatty acids.  This is honestly a really good study that I highly recommend you read if you can get access to it.


High fiber consumption has previously been linked to a lower incidence of colon cancer also, and so I am also wondering whether or not these short chain fatty acids may play a role in that, but obviously it is too early to tell for that.  


And of course with how much I write about weight loss, I’m also wondering if these may contribute to some of the different weight effects of the microbiome, but there haven’t been any good human studies I have seen examining that yet.


Now we do need to be careful because this is a somewhat small study, however, this does seem to be a convincing mechanism for the ability of fiber to help alleviate Type 2 diabetes.  It is important to always consult with your doctor or other medical professional before making any changes to your diet. However, this evidence seems to show to me the importance of fiber in maintaining a healthy gut microbiome.

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