Your Microbiome

What is your microbiome?

Many trillions of microorganisms live in and on us, many of which are in our gut. In fact, the cells of microbes in our bodies outnumber our human cells. Over thousands of years, our bodies have developed a symbiotic relationship with these organisms, generally supporting each other’s health and well-being. In exchange for food and lodging, these microorganisms perform these essential functions:¹Houghton D, Stewart CJ, Day CP, Trenell M. Gut microbiota and lifestyle interventions in NAFLD. International Journal of Molecular Sciences. 2016 Mar 25; 17(4):447; Dahiya DK, Renuka et al. Gut microbiota modulation and its relationship with obesity using prebiotic fibers and probiotics: a review. Frontiers in Microbiology. 2017 Apr 4;8:563; Mazzotti A, Caletti MT, Sasdelli AS, Brodosi L, Marchesini G. Pathophysiology of nonalcoholic fatty liver disease: lifestyle-gut-gene interaction. Digestive Diseases. 2016;34 Suppl 1:3-10; Tian S, Liu X, Lei P, Zhang X, Shan Y. Microbiota: a mediator to transform glucosinolate precursors in cruciferous vegetables to the active isothiocyanates. Journal of the Science of Food and Agriculture. 2018 Mar;98(4):1255-1260; Galland L. The gut microbiome and the brain. Journal of Medicinal Food. 2014 Dec;17(12):1261-72.

• Help with digestion and produce essential nutrients
• Support intestinal wall integrity
• Influence these functions and systems:
  • Metabolism
  • Sleep cycles
  • Brain and nervous system
  • Immune system, including inflammation 

Your microbiome is influenced both by your genetics and by your environment.²Hall AB, Tolonen AC, Xavier RJ. Human genetic variation and the gut microbiome in disease. Nature Reviews Genetics. 2017 Nov;18(11):690-699. Contact with other people, soil, decaying materials, foods, animals, and waste (fecal material) can introduce both good and harmful microbes to your body.

What can contribute to an out-of-balance microbiome?

Lifestyle 

Some behaviors can affect your microbiome composition and balance:³Jewell T. What Causes Dysbiosis and How Is It Treated? Healthline. February 1, 2019. Viewed September 20, 2022; Pole L, Hepp N. How can Eating Well help me? What the research says. CancerChoices. September 24, 2022. Viewed September 30, 2022; Lewis JD, Chen EZ et al. Inflammation, antibiotics, and diet as environmental stressors of the gut microbiome in pediatric Crohn’s disease. Cell Host & Microbe. 2015 Oct 14;18(4):489-500; Salavrakos M, Leclercq S, De Timary P, Dom G. Microbiome and substances of abuse. Progress in Neuro-Psychopharmacology and Biological Psychiatry. 2021 Mar 8;105:110113; Yao ZW, Zhao BC et al. Relationships of sleep disturbance, intestinal microbiota, and postoperative pain in breast cancer patients: a prospective observational study. Sleep and Breathing. 2020 Nov 19.

• Changing your diet to increase protein, fat, food additives, or sugar or other carbohydrates 
• Drinking two or more alcoholic beverages per day
• Poor dental hygiene, which allows bacteria in your mouth to grow out of balance
• Unprotected sex, which can expose you to harmful bacteria
• Use of stimulant drugs
• Sleep disturbance

Medical conditions

Medical treatments

• Antibiotics can dramatically alter your microbiome.¹⁰Zhang S, Chen DC. Facing a new challenge: the adverse effects of antibiotics on gut microbiota and host immunity. Chinese Medical Journal (England). 2019 May 20;132(10):1135-1138; Power SE, O’Toole PW, Stanton C, Ross RP, Fitzgerald GF. Intestinal microbiota, diet and health. British Journal of Nutrition. 2014 Feb;111(3):387-402; Lewis JD, Chen EZ et al. Inflammation, antibiotics, and diet as environmental stressors of the gut microbiome in pediatric Crohn’s disease. Cell Host & Microbe. 2015 Oct 14;18(4):489-500  
• Chemotherapy and radiotherapy can reduce the number of microbes and alter the composition of your microbiome, leading to dysbiosismicrobial imbalance or maladaptation on or inside the body.¹¹Montassier E, Gastinne T et al. Chemotherapy-driven dysbiosis in the intestinal microbiome. Alimentary Pharmacology and Therapeutics. 2015 Sep;42(5):515-28; Huang Y, Yang W et al. Effect of high-dose methotrexate chemotherapy on intestinal Bifidobacteria, Lactobacillus and Escherichia coli in children with acute lymphoblastic leukemia. Experimental Biology and Medicine (Maywood). 2012 Mar;237(3):305-11; Montassier E, Gastinne T et al. Chemotherapy-driven dysbiosis in the intestinal microbiome. Alimentary Pharmacology & Therapeutics. 2015 Sep;42(5):515-28; van Vliet MJ, Tissing WJ et al. Chemotherapy treatment in pediatric patients with acute myeloid leukemia receiving antimicrobial prophylaxis leads to a relative increase of colonization with potentially pathogenic bacteria in the gut. Clinical Infectious Diseases. 2009 Jul 15;49(2):262-70; Montassier E, Batard E et al. 16S rRNA gene pyrosequencing reveals shift in patient faecal microbiota during high-dose chemotherapy as conditioning regimen for bone marrow transplantation. Microbial Ecology. 2014 Apr;67(3):690-9; Touchefeu Y, Montassier E et al. Systematic review: the role of the gut microbiota in chemotherapy- or radiation-induced gastrointestinal mucositis—current evidence and potential clinical applications. Alimentary Pharmacology & Therapeutics. 2014 Sep;40(5):409-21.

Risk factors for an imbalanced microbiome

• Advanced age¹²Power SE, O’Toole PW, Stanton C, Ross RP, Fitzgerald GF. Intestinal microbiota, diet and health. British Journal of Nutrition. 2014 Feb;111(3):387-402.

The role of fiber and short-chain fatty acids

Intestinal bacteria ferment dietary fiber into the short-chain fatty acids (SCFAs) butyrate, acetate, and propionate. These SCFAs are absorbed in your intestine and play an important role in energy metabolism. Butyrate in particular provides energy for the epithelial cells in the colon. Butyrate also maintains intestinal integrity, inhibits inflammation and carcinogenesis, promotes a feeling of fullness after a meal (satiety), and decreases oxidative stressan imbalance between free radicals and antioxidants in your body; this imbalance can cause harmful oxidation reactions in your body chemistry.¹³Hartstra AV, Bouter KE, Bäckhed F, Nieuwdorp M. Insights into the role of the microbiome in obesity and type 2 diabetes. Diabetes Care. 2015 Jan;38(1):159-65; Hamer HM, Jonkers D et al. Review article: the role of butyrate on colonic function. Alimentary Pharmacology and Therapeutics. 2008 Jan 15;27(2):104-19. The other SCFAs enter the bloodstream (venous system). Short-chain fatty acids also affect immune cell function.¹⁴Alvarez-Curto E, Milligan G. Metabolism meets immunity: the role of free fatty acid receptors in the immune system. Biochemical Pharmacology. 2016 Aug 15;114:3-13.

Some evidence shows that a lack of these SCFAs or the microbes that produce them is linked to the development of intestinal disease, inflammatory bowel diseases, and colorectal cancer.¹⁵Hartstra AV, Bouter KE, Bäckhed F, Nieuwdorp M. Insights into the role of the microbiome in obesity and type 2 diabetes. Diabetes Care. 2015 Jan;38(1):159-65. 

Either too low or too high a concentration of SCFAs shows an imbalance and higher risk of poor health outcomes. High concentrations of SCFAs are linked to obesity, for example.¹⁶Scheithauer TP, Dallinga-Thie GM, de Vos WM, Nieuwdorp M, van Raalte DH. Causality of small and large intestinal microbiota in weight regulation and insulin resistance. Molecular Metabolism. 2016 Jun 10;5(9):759-70. 

Helpful links

Gacesa R, Kurilshikov A et al. Environmental factors shaping the gut microbiome in a Dutch population. Nature. 2022 Apr;604(7907):732-739.

Dill-McFarland KA, Tang ZZ et al. Close social relationships correlate with human gut microbiota composition. Scientific Reports. 2019 Jan 24;9(1):703.

Bai-Tong SS, Thoemmes MS et al. The impact of maternal asthma on the preterm infants’ gut metabolome and microbiome (MAP study). Scientific Reports. 2022 Apr 19;12(1):6437.

Ursell LK, Metcalf JL, Parfrey LW, Knight R. Defining the human microbiome. Nutrition Reviews. 2012 Aug;70 Suppl 1(Suppl 1):S38-44.

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