Gut Health Continued — by Kirstin Kadé
written by Kirstin Kade from Taste & See
In my last post about gut health, I shared a brief overview of what exactly the gut microbiome is, and how you can best look after it through the food that you eat and certain lifestyle factors. Today, I want to take a closer look at the main functions of our gut microbiome, and how it functions to best look after us!
Whilst many bacteria and fungi are associated with illness, the vast majority of the microbes found in our gut are actually important for ensuring the proper functioning of our immune system. Our gut is one of the places where the outside world comes into contact with our sterile internal environment, and thus our gut microbiome acts as an important defensive barrier (or ‘army’) that is trained to react and defend the body against harmful intruders, including both pathogenic microorganisms and toxins. They do this both directly and indirectly, by attacking unwanted visitors and through the stimulation of the immune system to ‘send in troops’ as backup to help fight off invaders.
Research has shown that our gut microbiota has a dynamic relationship with our innate and adaptive immune system, and influences many aspects related to how it develops and functions from the time we are born. Gut-associated lymphoid tissue (GALT), which forms the first line of defense controlling the passage of substances that are allowed to enter the body through the production of secretions such as secretory immunoglobulin A, relies on the communication between our gut microbiota and immune cells to function properly. If all this sounds like another language to you, this website does a good job of explaining how our immune system is divided and how it works.
Digestion & production of SCFAs
Our gut microbes have the amazing ability to help us digest and absorb many of the nutrients found in the food that we eat that we would normally be unable to access. Beneficial colonic bacteria express enzymes that are able to break down and ferment otherwise indigestible dietary fibre, during which they produce a number of metabolic by-products including short-chain fatty acids (SCFAs).
SFCAs are quickly absorbed by our intestinal cells and have a number of different functions in the body, such as:
Providing an important energy source for cells in our colon
Cell gene expression, differentiation, proliferation, and apoptosis (cell death)
Anti-inflammatory and anticancer activity (more specifically the SCFA butyrate, which also has a possible role to play in preventing and managing inflammatory bowel diseases)
Enhancement of the gut barrier function
Regulation of our immune system and inflammatory response
Regulation of hepatic lipid and glucose homeostasis
Nutrient synthesis & absorption
Another really interesting function of our gut microbes is the fact that they are able to synthesise some of the important micronutrients that our bodies require to function properly. Research has shown that some members of the human gut microbiota are able to produce vitamin K, as well as many of the B-vitamins (including biotin, B12, folate, thiamine, and nicotinic acid). For anyone that wants to learn a bit more about exactly how they do this, go and give this paper a read. Our gut bacteria also have the ability to enhance the absorption of minerals such as calcium, iron, and magnesium from the intestinal tract, and play a role in regulating our amino acid pool through the production and absorption of some amino acids and the breakdown of others.
Brain function & mental health
It’s only fairly recently that scientists have recognised the important role that our gut microbiota has to play in relation to our mental health and mood. The microbiota-gut-brain axis is a two-way communication network that includes branches of our nervous system (including a unique division known as the enteric nervous system), neuroendocrine and neuroimmune pathways, and our gut microbiota. This communication pathway allows our brain to influence the secretion, movement, and sensory functions in the GIT, and conversely allows the gut (and gut microbes contained within it) to send messages back to the brain. One of the ways that our gut microbes are able to send messages is through their synthesis neurotransmitters, such as serotonin, which influence our brain function and behavior.
Research has shown differences between the gut microbiota of individuals suffering from a number of psychological disorders, including depression, compared with healthy people, suggesting that our gut microbes may have a role to play in mental health disorders. Some scientists even believe that our intestinal microbiota may manipulate our eating behavior in order to increase their fitness through a number of different mechanisms, including generating cravings for foods that they need or that will prevent the growth their competitors and through neural stimulation. Irritable bowel syndrome (IBS), which a functional gut disorder associated with stress and changes in mood, may also be related to the gut microbiota. For anyone interested in reading a bit more about this connection, go check out this paper.
An ongoing field of research
Although these are some of the main functions of our gut microbiota, the mechanisms behind many of them are still largely unknown and rather complex and there is currently lots of research being done within this fascinating and complex field. If this is a subject that interests you as much as it interests me, take the time to read through the references that I’ve cited below. It might take a while to get through it all, but it’ll be well worth it. Our gut microbiome is truly fascinating!
1 — Gut Microbiota for Health. Gut microbiota info [Internet]. Available from: http://www.gutmicrobiotaforhealth.com/en/about-gut-microbiota-info/.
2 — Kennedy P, Murphy AB, Cryan JF, Ross PR, Dinan TG, Stanton C. Microbiome in brain function and mental health. Trends Food Sci Technol. 2016 Nov;56(B):289-301. Available from: https://www.sciencedirect.com/science/article/pii/S0924224416301741.
3 — Reigstad CS, Salmonson CE, Rainey JF, Szurszewski JH, Linden DR, Sonnenburg JL, Farrugia G, Kashyap PC. Gut microbes promote colonic serotonin production through an effect of short-chain fatty acids on enterochromaffin cells. FASEB J. 2015 Apr;29(4):1395-1403. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25550456.
4 — Alcock J, Maley CC, Aktipis CA. Is eating behavior manipulated by the gastrointestinal microbiota? Evolutionary pressures and potential mechanisms. Bioassays. 2014 Oct;36(10):940-9. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25103109.
5 —Bertrand P, Loughman A, Jackson M. Gut feeling: how your microbiota affects your mood, sleep and stress levels [Internet]. The Conversation. 10 October 2016 (cited 31 Jan 2018). Available from: http://theconversation.com/gut-feeling-how-your-microbiota-affects-your-mood-sleep-and-stress-levels-65107.
6 — Sekirov I, Russell SL, Antunes LC, Finlay BB. Gut Microbiota in Health and Disease. Physiol Rev. 2010 Jul;90(3):859-904. Available from: https://www.ncbi.nlm.nih.gov/pubmed/20664075.
7 — Thursby E, Juge N. Introduction to the gut microbiota. Biochem J. 2017 Jun 1;474(11):1823-36. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5433529/.
8 — Purchiaroni F, Tortora A, Gabrielli M, Bertucci F, Gigante G, Ianiro G, Ojetti V, Scarpellini E, Gasbarrini A. The role of intestinal microbiota and the immune system. Eur Rev Med Pharmacol Sci. 2013 Feb;17(3):323-33. Available from: https://www.ncbi.nlm.nih.gov/pubmed/23426535.
9 — LeBlanc JG, Milani C, de Giori GS, Sesma F, van Sinderen D, Ventura M. Bacteria as vitamin suppliers to their host: a gut microbiota perspective. CurrOpin Biotechnol. 2013;24:160-68. Available from: https://www.ncbi.nlm.nih.gov/pubmed/22940212.
10 —Lin R, Liu W, Piao M, Zhu H. A review of the relationship between the gut microbiota and amino acid metabolism. Amino Acids. Dec 2017;49(12):2083-90. Available from: https://link.springer.com/article/10.1007%2Fs00726-017-2493-3.
11 — Distrutti E, Monaldi L, Ricci P, Fiorucci S. Gut microbiota role in irritable bowel syndrome: New therapeutic strategies. World J Gastroenterol. 2016 Feb 21;22(7):2219-2441. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4734998/pdf/WJG-22-2219.pdf.
Kirstin is a qualified Food Scientist and is currently studying a MSc Human Nutrition at the University of Surrey in the U.K. Her blog, Taste & See, is a space where she shares nutrition-related knowledge and wholesome recipes that aim to make good health through food accessible to others.