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Dysbiosis is the term for a bacterial imbalance within the digestive tract. Your bowels contain as many as 100 trillion bacteria - more than the total number of cells in the human body - with up to 1000 different species playing a crucial role in gut health. Ideally, you want most of your bowel bacteria to be beneficial lactic acid producing types, such as Lactobacilli and Bifidobacteria, with fewer of the less beneficial types of bacteria which tend to produce gas and unpleasant odours. When the balance of bacteria becomes disordered, so the less desirable bacteria outnumber the good, then you have dysbiosis or dysbacteriosis.
Your bowel is designed to empty regularly, which means you lose beneficial probiotic bacteria every day alongside their less desirable relatives. Normally, these 'good' bacteria are replenished by the multiplication of bacteria that adhere to the gut wall, and which live within your appendix (if you still have one) as this blind pouch acts as a bacterial reservoir.
The type of diet you eat has a profound effect on your bowel bacterial balance, as different species of bacteria thrive on different types of carbohydrate, fibre and protein. Emerging research in non-human primates suggests that following a Mediterranean style diet, which provides lots of vegetables, fish and olive oil may increase levels of probiotic bacteria in the gut by almost 10% compared with a meat-rich Western-style diet.1 It's likely that similar effects will occur in humans, too. Lifestyle factors such as alcohol and smoking can impact your bowel bacterial balance, too.2
Dysbiosis develops when levels of probiotic bacteria are reduced and other species of bacteria become overly abundant. This can occur at any time but is most common after taking broad-spectrum antibiotics, which kill off your 'good' probiotic bacteria as well as harmful infections.3
Another factor that affects gut microbial balance is physical and psychological stress, which suppresses immunity and increases bowel emptying as part of the fight or flight response (to make you lighter for running).
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The balance of bacteria within the bowel has a surprising influence on general health, from how well you digest food and absorb vitamins and minerals, to how you process medicines.
Bowel bacteria help to prime your immune system to fight infections and regulate the production of serotonin within the bowel wall which regulates bowel contractions. As a neurotransmitter, serotonin is also involved in regulating mood within the brain. It's therefore not surprising that dysbiosis can produce a wide range of both physical and psychological symptoms, but it is often overlooked as a cause of ill health.
Gut dysbiosis is believed to play a role in many long-term (chronic) conditions, including irritable bowel syndrome and inflammatory conditions such as ulcerative colitis4 and rheumatoid arthritis. Dysbiosis has also been associated with anxiety and depression, and even with weight gain and type 2 diabetes5 through effects on hunger hormones and insulin resistance.
The exact way in which dysbiosis causes numerous symptoms throughout the body is not fully understood, but theories include:6
The early symptoms of dysbiosis mainly affect the bowel, and one of the first signs of abnormal fermentation is bloating. This can progress to cause a change in bowel habit, such as constipation or diarrhoea, often with cramping pains. While these symptoms may be compatible with irritable bowel syndrome, this is not a diagnosis you should make yourself. Always seek medical advice if you experience a change in bowel habit - especially if you also notice other red flag symptoms such as unexpected weight loss or blood in the stools (these can be a sign of bowel cancer which, when diagnosed early is more easily treated).
Other symptoms that can be a sign of dysbiosis include fatigue, joint pain, poor concentration, anxiety and even depression7. Different people will experience different symptoms, based partly on the balance of bacteria present in their bowel, and the way these interact with the genes you have inherited.
Scientists recently discovered we may all belong to one of three different patterns of gut bacteria, or enterotypes, which are as distinct as your blood group.8 Your bacterial balance - whether Bacteroides dominant, Prevotella dominant or Ruminococcus dominant - appears to affect your efficiency in extracting energy from food, and may explain why some people find it harder to lose weight than others.
Your gut bacteria pattern may even dictate how well you react to some drugs, the diseases you develop, and your susceptibility to vitamin deficiencies. People in the Bacteroides group had better levels of vitamins C, B2 and B5, for example, while those in the Prevotella group have higher levels of B1 and folate.
It seems that just about any persistent physical or psychological symptom could be related to dysbiosis. If you are experiencing continuing health problems, it's important to see your doctor.
Currently, there is little medical recognition of the role dysbiosis may play in human health and your doctor is unlikely to immediately pounce on a stool sample. Researchers predict, however, that within five years, doctors will assess your microbiome and prescribe drug treatments and doses based on your gut type as a form of personalised medicine. The use of gut microbe transplants (known as a trans-poo-sion) may even become mainstream.
In the meantime, the best way to help maintain a healthy microbial balance in your intestines is to eat a healthy, Mediterranean-style diet and to replenish your probiotic bacteria regularly - ideally daily - with a probiotic supplement. Prebiotics (eg fructo-oligosaccharides) also help to promote the growth and survival of probiotic bacteria by providing your 'good' bacteria with a food source they can ferment to flourish.
If you'd like to read more about the benefits of keeping a healthy gut, select Digestion from the Your health menu above.
Dr Sarah Brewer is Healthspan's Medical Director and holds degrees in Natural Sciences, Surgery and Medicine from the University of Cambridge. Having worked as a GP and hospital doctor, Dr Sarah now holds an MSc in Nutritional Medicine from the University of Surrey and specialises in nutrition. She is also an award-winning writer and author.
Nothing beats a healthy, balanced diet to provide all the nutrients we need. But when this isn't possible, supplements can help. This article isn't intended to replace medical advice. Please consult your healthcare professional before trying supplements or herbal medicines.
1Nagpal R et al. (2018). Gut Microbiome Composition in Non-human Primates Consuming a Western or Mediterranean Diet, Frontiers in Nutrition
2Capurso, G & Lahner, E, 2017. The interaction between smoking, alcohol and the gut microbiome. Best Practice & Research, Clinical Gastroenterology, vol 31, no.5, pp 579-588
3Hawrelak, JA, & Myers, SP, 2004. 'The Causes of Intestinal Dysbiosis: A Review', Alternative Medicine Review, vol 9, no 2
4Duranti, S et al, 2016. Elucidating the gut microbiome of ulcerative colitis: bifidobacteria as novel microbial biomarkers, FEMS Microbiology Ecology, vol 92, no 12, fiw191
5Jie, Z et al, 2017. The gut microbiome in atherosclerotic cardiovascular disease, Nature Communications, vol 8, no 1, 845
6Conlon, MA, & Bird, AR, 2015. The Impact of Diet and Lifestyle on Gut Microbiota and Human Health, Nutrients, vol 7, no 1, pp 17-44
7Foster, JA, & McVey Neufeld, KA, 2013. Gut-brain axis: how the microbiome influences anxiety and depression, Trends In Neurosciences, vol 36, no 5, pp 305-312
8AFP (2011). Three types of human gut bacteria found, www.abc.net.au