How important is it having a healthy gut microbiome, and could it help control blood sugar levels?
The gut microbiome, as defined by molecular biologist Joshua Lederberg, consists of all the microorganisms in the gastrointestinal tract (GIT). The microorganisms include bacteria, protozoa, viruses, and fungi and their collective genetic material. The gut microbiota consists of all the bacteria, pathogenic and commensal, residing in the GIT. The gut microbiota has been explored for potential interactions between the microbe and host which could affect immunity, metabolism, and neuroendocrine responses. The gut microbiota plays an important role in nutrient and mineral absorption, synthesis of enzymes, vitamins and amino acids, and the production of short-chain fatty acids (SCFAs). 
The fermentation by-products propionate, butyrate, and acetate, are important for gut health and provide energy for epithelial cells, provide immunomodulation and protection against pathogens, and enhance epithelial barrier integrity. The development and alteration of the gut microbiome are affected by a variety of factors including birthing method, infant feeding method, exposure to the environment, stress, diet, medications, comorbid diseases, such as diabetes and obesity, and the stage of the lifecycle. Dysbiosis is described as the alteration in the microbial community that results in decreased numbers and diversity of commensal bacteria. Studies suggest relationships between gut dysbiosis and chronic health conditions such as inflammatory bowel disease, metabolic syndrome, cardiovascular disease, obesity, and cancer. This article will focus on the effect of the gut microbiota on blood sugar control, whether a healthy gut microbiome can help in controlling blood sugar levels and insulin and what foods can help maintain a healthy gut microbiome. 
Effect of the microbiome on gut serotonin production and blood sugar levels
Australian and Canadian researchers have discovered that certain gut bacteria can directly influence blood sugar levels by promoting the synthesis of gut-derived serotonin. Serotonin is the neurotransmitter that influences feelings of happiness and regulates mood. The molecule has other broad effects across the entire body. Over 90 percent of serotonin produced by the human body is located in the gut. As serotonin is not able to cross the blood-brain barrier, these intestinal secretions are not thought to directly influence our brain. Instead, blood and gut serotonin levels seem to play an important role in our overall metabolic profile. 
In obese people, for example, higher levels of circulating serotonin have been detected than in normal-weight subjects, suggesting that serotonin can influence weight regulation. Using both genetic and pharmacological animal models, the research discovered gut microbiome alterations did result in disruptions to intestinal serotonin synthesis, and these factors could be correlated with improvements in glucose handling. This means that the higher the gut and blood serotonin levels, the worse a body's glucose handling. “We found that the microbiome worsens our metabolism by signaling to cells in the gut that produce serotonin,” says Damien Keating, from Australia’s Flinders University, and corresponding author on the new study. “They drive up serotonin levels, which we previously showed to be increased in obese humans, and this rise in blood serotonin causes significant metabolic problems.” 
The link between gut microbiome and diabetes
There is good evidence that the gut microbiome plays an important role in glucose metabolism, insulin sensitivity, and overall energy homeostasis. However, researchers have not been able to establish which specific bacteria can be associated with positive metabolic outcomes regarding type 2 diabetes. 
Bacteroides and Bifidobacterium are the two bacterial genera most frequently identified as potentially protective against type 2 diabetes. Ruminococcus, Fusobacterium, and Blautia, on the other hand, are more consistently detected in higher levels in patients with type 2 diabetes. 
The most common combination was with Bifidobacterium, leading the researchers to suspect the microbes may work in a synergistic way to protect against type 2 diabetes. In a recently published study, it is suggested that gut bacteria might be somewhat responsible for the onset of type 2 diabetes and it could be the result of bacteria crossing the intestinal barrier into other tissue in the body. This process is called bacterial translocation. 
André Marette, the lead author of the study found the following: “Our findings suggest that in people suffering from severe obesity, bacteria or fragments of bacteria are associated with the development of Type 2 diabetes. We know that the intestinal barrier is more permeable in obese patients. We hypothesize that living bacteria and bacterial fragments cross this barrier and set off an inflammatory process that ultimately prevents insulin from doing its job, which is to regulate blood glucose levels by acting on metabolic tissues." 
How can you keep your gut microbiome healthy to promote an overall healthier body?
What you feed your microbiome may have the biggest impact on its health. The healthier your microbiome is, the healthier you are. Nourishing a balance among the nearly 1000 different species of bacteria in your gut is key to a healthy microbiome. There are two ways to maintain this balance: adding living microbes directly to your system (probiotics) and helping the microbes already there to grow by giving them the foods they like (prebiotics). 
Probiotics contain live organisms, usually specific strains of bacteria that directly add to the population of healthy microbes in your gut. You can take probiotics through both food and supplements. The most common probiotic food is yogurt. Yogurt is made by fermenting milk with different bacteria, which are left in the final product. Other bacteria-fermented foods, such as sauerkraut, kimchi, and kombucha, are also good sources of probiotics. 
Prebiotics are specialized plant fibers. They act like fertilizers that stimulate the growth of healthy bacteria in the gut. Prebiotics are found in many vegetables and fruit, especially those that contain complex carbohydrates, such as resistant starch and fiber. These vegetables and fruit include artichokes, garlic, onion, leeks, asparagus, apples, cocoa, and grapefruit. These carbohydrates are not digestible by your body, so they pass through the digestive system to become food for the bacteria and other microbes. 
As discussed above, the gut microbiome has many essential functions in the body and making sure it is healthy is important for overall health. Feeding the healthy bacteria in your gut with pre- and probiotics are essential for positive gut microbiome alterations which could improve glucose handling. A healthy gut microbiome will also help with intestinal barrier integrity. This would prevent bacterial translocation which would help in preventing insulin resistance caused by inflammatory processes. A healthier gut microbiome means a healthier you. Make sure to feed your gut bacteria today!
- Cresci G, Izzo K. Chapter 4: Gut Microbiome. Adult Short Bowel Syndrome. Academic Press; 2019. p.45-54. Available from: https://www.sciencedirect.com/science/article/pii/B9780128143308000044
- New Atlas. Rich Haridy [Internet]. Microbiome found to influence gut serotonin production and blood sugar levels. Cited 2019 September 16. Available from: https://newatlas.com/medical/microbiome-gut-bacteria-serotonin-blood-sugar-metabolism/
- New Atlas. Rich Haridy [Internet]. Gut microbiome studies reveal new bacterial links with diabetes. Cited 2020 March 10. Available from: https://newatlas.com/science/gut-microbiome-bacteria-diabetes-metastudy-metabolism/
- Mayo Clinic [Internet]. Prebiotics, probiotics and your health. Cited 2019 May 21. Available from: https://www.mayoclinic.org/prebiotics-probiotics-and-your-health/art-20390058