Tuesday 22 May 2018

The microbiome in the small intestine

Most research into the intestinal microbiome focuses on the large intestine. To date, very little attention has been paid to the small intestine. New research changes this; this has revealed that the microbes in the small intestine can directly regulate the absorption of fat.

Research into the small intestine - and the microbiome that resides in it – appears to be accelerating. Last year, for example, a study involving rodents at Princeton University revealed that ninety percent of the fructose in the small intestine is digested. The small intestine is unable to cope with an excess of fructose and this is directed to the liver. However, it can also end up in the large intestine, which the microbiome isn’t equipped for. A negative effect on the microbiome is probable, with the resultant consequences. 


New research

 A new study of the small intestine demonstrates that the typical high-calorie Western diet can lead to an increase in microbes, the majority of which are unfavourable for Westerners. As a response to fatty foods, they can multiply in the small intestine within 24 to 48 hours and help facilitate the digestion and absorption of fatty foods. 
Two groups of mice were studied. The first group was germ-free, bred in isolated rooms and no intestinal bacteria were present. The second group was specific pathogen-free (SPV); they were healthy and only non-pathogenic microbes were present. The germ-free mice were given a high-fat diet but were not capable of digesting or absorbing the fat. Their faeces contained elevated lipid levels.
The SPV mice who were given a high-fat diet did put on weight. The diet quickly increased the abundance of certain microbes in the small intestine, including microbes from the Clostridiaceae and Peptostreptococcaceae families. A member of the Clostridiaceae family was found to specifically influence fat absorption. When their fatty diet was supplemented with Bifidobacteriacaea and Bacteriodacaea, which are often associated with slimness, the abundance of other bacterial families decreased. The germ-free mice were then given microbes that aid fat digestion, then they also quickly acquired the ability to absorb lipids. 



The findings suggest that the aforementioned microbes facilitate the production and separation of digestive enzymes in the small intestine. Those digestive enzymes break down dietary fats, which enables rapid absorption of high-calorie food. At the same time, the microbes secrete bioactive compounds. These compounds stimulate the absorbent cells in the intestine to transport fat for absorption. The constant presence of these microbes, which make lipid absorption more efficient, can over time lead to overeating and obesity. This is one of the first studies to prove that specific small intestine microbes directly regulate the digestion and absorption of lipids. 


The small intestine has a more important role than thought to date. What we eat each day has a significant impact on the quantity and quality of the microbiome in the small and large intestine. The diet can elicit specific bacterial strains in the small intestine, meaning the host is more capable of digesting and absorbing food. This can even have an impact on other organs, such as the pancreas.
Combatting obesity can focus on reducing the excessive presence or activity of certain microbes that stimulate fat absorption. But also on increasing the presence of microbes that can inhibit fat absorption.Further to this study, more research is needed. However, the results suggest that prebiotics or probiotics could be used to combat obesity, but also malabsorption disorders, such as Crohn’s disease. Ultimately, postbiotics (compounds or metabolites derived from bacteria) could even be developed to improve the absorption of nutrients.



Jang, C. et al. The Small Intestine Converts Dietary Fructose into Glucose and Organic Acids. Cell Metab. 2018 Feb 6;27(2):351-361.e3. doi: 10.1016/j.cmet.2017.12.016.

Martinez-Guryn, K. et al. Small Intestine Microbiota Regulate Host Digestive and Absorptive Adaptive Responses to Dietary Lipids. Cell Host & Microbe , Volume 23 , Issue 4 , 458 - 469.e5