Gut bacteria are types of microorganisms that live within the human digestive system alongside other tiny organisms like fungi and viruses. Together, they form the “microbiome”. You may have noticed that there has been a lot of talk in health news about the microbiome, probiotics, gut bacteria and health – so, we’re going to break it down for you and make it easier to digest!
Bacteria live throughout the human body but the 100 trillion that live in the digestive system may have the biggest impact on health. You may have heard of Lactobacillus acidophilus or Bifidobacterium longum – these are types of beneficial bacteria that are commonly found in the gastrointestinal tract, but the type and number of bacteria found in your gut is completely unique to you. No 2 people have the exact same microbiome, but beneficial gut bacteria perform much the same function in everybody:
What do gut bacteria do?
Beneficial gut bacteria – the types that live symbiotically with us – perform the following essential functions:
- Digest and break down some nutrients into their absorbable forms 
- Reduce inflammation by secreting anti-inflammatory chemicals 
- Ferment carbohydrates in the large intestine to create by-product nutrients like short-chain fatty acids 
- Strengthen the intestinal wall to form a protective barrier against pathogens 
- Educate the immune system about which pathogens to attack 
- Stimulate immune cells to grow and mature 
- Secrete chemicals that kill off harmful bacteria, viruses, and fungi 
- Regulate hormones and chemicals that are released from the gut 
- Communicate directly with the immune, endocrine, and nervous systems 
Negative, harmful, or pathogenic bacteria do much the opposite. They promote inflammation, cause illness, initiate disease, and can disrupt signals and functions of other body systems.
The balance of beneficial vs harmful gut bacteria has a major impact on human health.
Do gut bacteria affect human health?
There is increasing research showing associations between gut microbiome and health but more research is needed. 
“We have known for decades that gut bacteria communicate directly with our immune systems, and the latest research suggests that this communication extends to other body systems too. The types of bacteria found in the intestines may have an even greater impact on our health than we once thought possible.”
– Dr Paul Vanderwalle, Principal Scientific Consultant at Clasado
Improving the health of our gut bacteria can certainly improve our digestion to relieve issues like constipation and diarrhoea, and researchers now believe that the diversity of the microbiome directly impacts our ability to fight off and heal from many serious diseases. Studies have found that people with coeliac disease, diabetes, eczema, arthritis or obesity have less diverse gut bacteria profiles, and this may contribute to the underlying causes of these conditions. 
- Digestive Health
Beneficial bacteria can reduce the risk and severity of all kinds of gastrointestinal diseases and can even reduce the symptoms of lactose intolerance. 
- Immune System
A study in 2009 showed that improving the health of the gut microbiome reduced the severity of the common cold in people who also ate well and exercised regularly . These helpful bacteria also crowd out pathogens that can cause systemic problems such as thrush and keep inflammation within healthy levels throughout the body. 
One study found that leaner subjects had more robust and diverse gut bacteria populations than obese people , and other studies have shown that increasing particular types of gut bacteria can improve weight loss and how fat is stored in the body.
- Mood & Mental Health
Other research has shown that the types of bacteria found in the microbiome directly influence our mood and cognition by controlling chemicals such as serotonin and dopamine , and the health of the gut may be linked to conditions like depression, anxiety and psychiatric disorders. 
- Skin Health
Beauty really does come from within – the types of bacteria found in the gut have been shown to influence the severity of acne, eczema and psoriasis. Beneficial gut bugs can reduce redness, balance oils on the skin and may even have anti-ageing effects on wrinkles and sun spots.  
The link between the microbiome and human health is broader than experts first suspected, and it now appears that gut bacteria influence our total health, from head to toe. One thing is for sure, taking care of your gut bacteria can only be a good thing.
 Valdes, A. M., et al. (2018) Role of the gut microbiota in nutrition and health. BMJ., 361. https://www.bmj.com/content/361/bmj.k2179
 Belkaid, T. & Hard, T., et al. (2014) Role of the Microbiota in Immunity and inflammation. Cell, 157:1, 121 – 141. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4056765/
 Rowland, I., et al. (2018) Gut microbiota functions: metabolism of nutrients and other food components. Eur J Nutr., 57:1, 1 – 24. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5847071/
 Kelly, J. R., et al. (2015) Breaking down the barriers: the gut microbiome, intestinal permeability and stress-related psychiatric disorders. Front Cell Neurosci., 9, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4604320/
 de Vrese, M., et al. (2001) Probiotics – compensate for lactase insufficiency. Am J Clin Nutr., 73:2, 421 – 429. http://ajcn.nutrition.org/content/73/2/421s.full
 West, N. P., et al. (2009) Probiotics, immunity and exercise: a review. Exerc Immunol Rev., 15, 107 – 126. https://www.ncbi.nlm.nih.gov/pubmed/19957873
 Özdemir, Ö. (2010) Various effects of different probiotic strains in allergic disorders: an update from laboratory and clinical data. Clin Exp Immunol., 160:3, 295 – 304. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2883099/
 Ley, R. E., et al. (2006) Microbial ecology: human gut microbes associated with obesity. Nature., 444, 1022 – 1023. https://www.ncbi.nlm.nih.gov/pubmed/17183309
 Kadooka, Y., et al. (2010) Regulation of abdominal adiposity by probiotics (Lactobacillus gasseri SBT2055) in adults with obese tendencies in a randomized controlled trial. Eur J Clin Nutr., 64:6, 636 – 643. https://www.ncbi.nlm.nih.gov/pubmed/20216555/
 Indigenous bacteria from the gut microbiota regulate host serotonin biosynthesis.
Yano JM, Yu K, Donaldson GP, Shastri GG, Ann P, Ma L, Nagler CR, Ismagilov RF, Mazmanian SK, Hsiao EY
Cell. 2015 Apr 9; 161(2):264-76. https://www.ncbi.nlm.nih.gov/pubmed/25860609/
 Microbiota, immunoregulatory old friends and psychiatric disorders.
Rook GA, Raison CL, Lowry CA
Adv Exp Med Biol. 2014; 817():319-56.
 Kim, Y. A., et al. (2018) Probiotics, prebiotics, synbiotics and insulin sensitivity. Nutr Res Rev., 31:1, 35 – 51. https://www.ncbi.nlm.nih.gov/pubmed/29037268
 Kober, M. M. & Bowe, W. P. (2015) The effect of probiotics on immune regulation, acne, and photoaging. Int J Womens Dermatol., 1:2, 85 – 89. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5418745/
 Groeger, D., et al. (2013) Bifidobacterium infantis 35624 modulates host inflammatory processes beyond the gut. Gut Microbes, 4:4, 325 – 339. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3744517/