Why your gut microbiome should matter to you

The more scientists understand about the gut microbiome, the more closely linked to our overall health it seems to be.

Your microbiome, or more accurately ‘microbiota’, is the collection of bacteria and other microbes that live, usually harmoniously, in and on your body. They are found on your skin, in your gut and in your mouth and nose, among other places.

The microbiome of the gut is especially interesting as scientists have discovered it is involved in your weight, the health of your immune system, and how likely you are to suffer from various illnesses.

Each of us has a gut microbiome unique to us, shaped by our diet, our lifestyle and environment and our upbringing. The composition of this microbiome can change on a daily basis, based on what you eat and how you eat it. Variety in the microbial species that live in your gut is considered a sign of health.

Here are some reasons why you should care about your gut microbiome:

1. It helps you maintain a healthy weight

If you care about losing weight, you should care about your microbiome. A lack of variety in the species of your microbiome or a predominance of certain species, can predispose you to obesity.

Obese people have been shown to have more bacteria of a group called Firmicutes than lean people and they have fewer Bacteroidetes bacteria than lean people. This has opened up a whole exciting avenue of exploration for obesity researchers.

Eating a varied diet rich in fibre will help your microbiome to flourish and contain a diversity of different organisms, whereas eating lots of processed foods, and foods high in refined carbohydrates or saturated fats will upset the balance and allow unhealthy bacteria to take over.

Antibiotics, alcohol and stress also wipe out good bacteria and allow the undesirables to predominate.

2. It can affect your food cravings

It may just turn out that your food cravings are not yours after all. They may really be the cravings of the tiny microbes of your gut microbiome. And it seems not all of our microbes have our best interests at heart.

Some scientists are suggesting that microbes can generate cravings for the very foods that they need themselves to multiply and survive. We may be at their mercy, subject to cravings for fat and sugar that say more about what they want than what we want (or need).

It follows then, that the greater variety of bacteria that you have in your gut, the less chance that one group can become so powerful as to manipulate your tastes and cravings. Another reason perhaps that people who have a greater variation in species of bacteria in their gut are more likely to be a healthy weight.

The good news is that within a day, what you eat can start to influence that population of bacteria in your gut and turn it into a force for good health. Supporting the good bacteria by eating prebiotics (non-digestible fibre) and other healthy food can quickly make a difference.

3. Your gut is the powerhouse of your immune system

Scientists have known for years that a large part of the immune system is actually based in the gut. And recently, the role of the microbiome in regulating and providing some of that immunity is being discovered.

When babies are born, their guts are sterile and don’t contain any bacteria, but then quickly become colonised, until at around 3 years their gut microbiome starts to look like an adult’s.

The inside lining of your gut forms a selective barrier which prevents harmful bacteria, and substances such as allergens and toxins, from entering the body, but allows microscopic digested nutrients from your food to pass through.

To maintain this functional barrier, the gut has to be able to discriminate between beneficial microbes, which it wants to nurture, and disease-causing microbes, which it needs to eliminate as effectively as possible and prevent from passing through the intestinal wall into the body.

Part of the gut’s defence against harmful bacteria is that the real estate along the inside of the gut is taken up by the harmless bacteria of the microbiome, which help provide a physical and chemical barrier to keep out any invaders.

In addition to their physical presence, these normal resident bacteria in your gut also constantly stimulate your immune system gently, creating low grade inflammation to train it, by triggering it to release antibodies which prevent harmful bacteria from getting a foothold.

If this mutually beneficial relationship is disturbed, for example if substances like antibiotics or alcohol were to upset the balance, then harmful bacteria may penetrate the gut wall and give rise to inflammation in the body.

Recently, dysfunction and changes in the microbiome have been linked with the autoimmune diseases rheumatoid arthritis, type 1 diabetes, and multiple sclerosis. This is a major research focus for scientists as they try to work out the mechanisms of how these diseases are caused.

Could the rise in autoimmune diseases, where a person’s immune system reacts inappropriately to their own body tissues, be blamed on the state of our unhealthy gut microbiomes?

4. It helps you digest food

There are some foods that humans just can’t break down and digest without the help of the friendly bacteria of the gut microbiome. Fibre-rich foods such as oatmeal and brown rice and legumes such as peas, beans and lentils, are some of those foods.

These complex carbohydrates make it through the digestive system pretty much unscathed - until they reach the colon. It is in the colon where they are fermented by particular bacteria of the microbiome.

We humans don’t actually have the enzymes to digest fibre effectively. We need particular bacteria to ferment fibre and produce beneficial short-chain fatty acids like butyrate as a result. These resultant short-chain fatty acids have been shown to have favourable effects on health, reducing inflammation, diabetes and heart disease.

5. Your microbiome produces vitamins

Bacteria in your microbiome produce vitamins, including vitamin B12, thiamine (vitamin B1) and riboflavin (vitamin B2), and a form of vitamin K. (Vitamin K has a role in blood clotting.) So, although you obtain many vitamins from your food sources, your own population of gut bacteria can manufacture some of the vitamins you need.

6. Your gut bacteria can affect your mental health

It’s long been known that the brain and the digestive system are intimately linked. Most of us have experienced situations where stress or anxiety have affected us by producing gastrointestinal symptoms, such as diarrhoea or nausea. Conversely, gastrointestinal symptoms themselves can be the cause of anxiety or depression. Scientists use the term the ‘gut-brain axis’ to describe this 2-way signalling that occurs between the digestive system and the brain.

Interestingly, it is now thought that the microbial species of the gut microbiome may play a part in this signalling process. Several mechanisms have been suggested for how the microbes do this. These include by the microbes influencing the production of neurotransmitters (chemical messengers like serotonin), or by the end products (metabolites) the microbes produce from the digestion of food, such as butyrate.

Serotonin is a neurotransmitter that plays a role in depression. A lack of serotonin contributes to depression and anxiety. Recently, scientists have shown that some microbes in the gut can stimulate the body’s cells to produce more serotonin. Knowing that 90 per cent of serotonin is made in the gut, this is an exciting area still to be fully explored and may form the basis for future treatment of depression.

Also under investigation is the role of the microbiome in other mood disorders, such as anxiety. Researchers have shown that when they transplant the microbiome from stressed rats to rats that aren’t stressed, the second group of rats become stressed, implying that the microbiome is a potential cause of the mood disorder.

The holy grail of research will be whether, by improving the gut microbiome, scientists can reduce symptoms of mental health disorders such as anxiety and depression.

7. A healthy microbiome may protect you from allergy

Unfavourable changes to the microbiome, through eating a diet low in fibre or the use of antibiotics, may be linked to development of food allergies, and may have contributed to the rise in allergy that has occurred over past decades.

Many antibiotics kill bacteria indiscriminately and, although they are useful for fighting bacterial infections, sometimes they can also wipe out good bacteria, including those of the gut microbiome.

The lining of your gut normally functions as a selective barrier, allowing beneficial nutrients to pass through from your intestine into the bloodstream, but preventing toxins, harmful bacteria and allergic substances from getting through the layer of cells into your body and bloodstream.

However, if this selective barrier is compromised - known as intestinal hyper-permeability or ‘leaky gut’ - then the so-called ‘tight junctions’ between the epithelial gut cells may not be so tight. This may allow not just microscopic nutrients from food to pass through into the body, but also other substances that are normally excluded and which may cause allergy and inflammation.

Recently, scientists demonstrated that manipulating the gut microbiome in mice, so that it contained beneficial protective bacteria, resulted in keeping the mice safe from food allergies.

The scientists say this is because the bacteria were maintaining the intestinal barrier and preventing the allergic food substances from passing through the gut into the bloodstream, where they may trigger an allergic reaction.

Low fibre diets may cause the same leakiness of the gut wall and lead to allergy-causing substances passing into the body. This is because a low fibre diet results in less fermentation in the large intestine which causes a more alkaline environment. This can lead to a bloom of acid-sensitive bacteria, some of which are undesirable. Combine this increase in less desirable microbes with a reduction in the by-products of fermentation, many of which protect the gut wall, and you affect the integrity of the intestinal barrier - and there’s your leaky gut again.

Last Reviewed: 31 March 2017
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References

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