Guest blog by Vicky Ware
Bacterial Bonanza: Why do Probiotics Improve Our Health?
There has been a lot of hype about ‘good’ and ‘friendly’ bacteria in recent years – but what do these terms actually mean? Products containing bacteria range from pills to yoghurts to chocolate and even facial creams. These all claim health and beauty results because of the bacteria they contain but how many of their claims are based on evidence? Let me take you through why certain bacteria may be good for our health.
Your body has bacteria on every surface. Your skin, mouth and intestinal tract are all home to around 100 trillion bacteria – meaning bacterial cells outnumber your own cells by ten times 1. The combination of bacterial species which live on your body seem to be unique to each individual, making up a kind of ‘microbial finger print’. What your microbial fingerprint looks like differs depending on your genes and a multitude of other factors from whether you have ever taken antibiotics to whether you were breast fed as a baby 2.
Scientists think that there may be a ‘window of opportunity’ in early childhood during which time the microbial fingerprint of an individual is founded for the rest of their life 3. This time is so important that we seem to suppress our own immune systems during early life to allow bacteria to gain a firm footing inside us, ensuring we have a strong ecosystem going into adult life 4. I love the idea that bacteria are so essential to our health that we suppress our immune system to let them climb on board – it goes against the old way of thinking about ‘germs’ completely.
Why Does Our Microbial Fingerprint Matter?
Bacteria interact directly with our bodies. Our intestines are densely populated with bacteria and they also house a lot of the body's main immune defence systems. Scientists have found that the type of bacteria found in your intestine directly mould the way your immune system behaves. In fact, certain microbial fingerprints have now been linked to health problems as far ranging as obesity and allergic disease to schizophrenia, autism and depression 5.
Scientists think that changes in our microbiome might be responsible for the so called ‘Western diseases’ of chronic inflammation – diseases people living in more bacteria infested environments don’t get 6.
However we don’t yet know exactly what a ‘healthy’ microbiome looks like, or even if there is a one-size-fits all when it comes to which bacteria you should have in your intestine 7.
What Affects Our Microbial Fingerprint?
Pretty much everything you do affects which bacteria are able to live in your gut. For example, your bacteria can only eat what you eat, so if your diet is high in sugar and low in fibre, you’ll only have bacteria which can live off sugar and non which like to eat fibre 8;9. In the past, humans were probably exposed to many more bacteria through our diets and lifestyles than we are today and the foods they ate resulted in different bacteria surviving in their guts – we can get some insight into this through the microbiomes of hunter-gatherer people today 10.
The microbiome is an ecosystem. This means if one bacterial species is killed, other species will move into that ‘space’ in the system. If you take antibiotics, you are killing the majority of bacterial species, both the ones causing infection and the ones necessary for health. This is why people who take antibiotics often suffer from yeast infections – yeast are a fungi not bacteria so are not killed by antibiotics. The antibiotics reduce the numbers of bacteria in your microbiome, giving yeast more resources (food and space) to breed – and you get a yeast infection. This then makes it difficult for the bacteria to re-grow once you stop antibiotics as the yeast have taken over the system. Scientists think changes like these play a part in the fact that people who have taken antibiotics are more likely to develop allergic diseases such as asthma 11.
Probiotics are bacteria known to be good for human health. Considering the trillions of bacteria already in your gut, the bacteria found in one small pill don’t stand much of a chance once on the home turf of established colonies. Long-term supplementation, incorporating foods that naturally contain bacteria in to your diet and changing the types of food you eat is more likely to alter your microbiome 9.
There are some species which scientists think are definitely good for health, although it might be the ratio of one of these bacteria compared to another that is resulting in health benefits. Firmicutes and Bacteriodetes species seem to be the main bacteria found in the microbiome of healthy people, so foods containing them are the way to go if you’re interested in trying probiotics 12.
Probiotics have been shown to help with diarrhoea, especially traveller’s diarrhoea. They also seem to help some people with inflammatory bowel disease and Crohn’s disease. They may even help with conditions like asthma 13.
A recognised way of treating certain intestinal problems such as Inflammatory Bowel Disease and infection with C.difficile is a faecal transplant. Unfortunately, you did read that right the first time. Implanting a healthy persons faeces into someone with an intestinal problem has been found to help cure their disease because of the bacteria which get transplanted with the, er, other stuff 14.
These transplants are now being considered as a treatment for conditions such as metabolic disorders, neuropsychiatric disorders, autoimmune diseases and allergic disorders 14. The fact that we’re transplanting faecal matter rather than specific bacteria shows that we’re not certain yet which specific bacterial species are resulting in improved health.
In summary, we don’t fully know what changes our microbial fingerprint, or whether an adult microbiome can be changed in the long term. The ‘bacteria are good for health’ switch in thinking has been really exciting, for both the public and scientists, so it’s easy to get carried away when making conclusions on which bacteria are good for health. However, there are lots of probiotics and foods that help good bacteria live in on our bodies to make giving them a go worth a try.
Vicky has a degree in Biological Sciences with a focus on biochemistry and immunology and is currently studying for a MSc in Drug Discovery and Protein Biotechnology. She is also an endurance athlete.
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- Salonen, 2009. Microbial functionality in the human intestinal tract.
- Koch, 2015. Shaping the gut microbiome.
- Elahi, 2013. Immunosuppressive CD71+ erthroid cells compromise neonatal host defence against infection.
- Hill, 2012. Commensal bacteria-derived signals regulate basophil hematopoiesis and allergic inflammation.
- Devereux, 2006. The increase in prevalence of asthma and allergy: food for thought.
- Yong, 2014. There is no ‘healthy’ microbiome.
- Turnbaugh, 2007. The human microbiome project: exploring the microbial part of ourselves in a changing world.
- Turnbaugh, 2009. The effect of diet on the human gut microbiome: a metagenomic analysis in humanised gnotobiotic mice.
- Schnorr, 2014. Gut microbiome of the Hadza hunter-gatherers.
- Noverr, 2004. Development of allergic airway disease in mice following antibiotic therapy and fungal microbiota increase: role of host genetics, antigen, and interleukin-13.
- Huffnagle, 2014. Increase in dietary fiber dampens allergic responses in the lung.
- Xu, 2015. Fecal microbiota transplantation broadening its application beyond intestinal disorders.