Your gut, the super organ: how the microbiome affects your health

They populate your intestines by the trillion and are currently the focus of research: we’re talking about bacteria, fungi, viruses and protozoa. Scientists also refer to this diverse community of microorganisms as a microbiota or microbiome. Since the noughties, new technologies such as high-throughput sequencing have made it possible for the first time to analyse the enormous diversity of the intestinal flora) quickly and precisely – at least as far as intestinal bacteria are concerned. Several thousand types of bacteria have already been identified.

Around 300 of them are found in every human being. But a lot can influence intestinal flora: genetics, lifestyle, nutrition, medication such as antibiotics, pollutants, environmental influences, hygiene, whether you’ve (had) contact with pets or not. That’s why the tiny lodgers have hugely different compositions from one person to another. «They’re so individual that you could describe them as a microbial fingerprint,» says Professor Michael Scharl, doctor at the Clinic for Gastroenterology at the University Hospital Zurich (USZ) and head of the Translational Microbiome Research Center (web pages in German). He heads up Switzerland’s first microbiome consultations (website in German) at the USZ.

Your gut, the super organ: connected to the brain via a «highway»

One thing’s always the same: the more diverse the microbiome’s composition, the more resistant it is – equipping it for varied tasks. «It has long been known that intestinal bacteria help with digestion,» says Professor Scharl. «But now it’s also clear that microbes strengthen the intestinal barrier so that pathogens from the digestive organ can’t get into the body and vice versa. They also act as a training partner for the immune system and are involved in the formation of hormones, vitamins and other messenger substances.»

This is how the intestinal dwellers influence our entire metabolism, our organs and even our brain. Science also refers to this connection as the gut-brain axis (in German). The gut and brain communicate on this highway – which links the two organs – with the help of various messenger substances.

This includes substances produced by the bacteria entering the bloodstream via the intestinal wall. These include those that contribute to the production of neurologically active substances such as neurotransmitters serotonin and dopamine. So, it’s no wonder that the microbiome is also called the «super organ», when it can even influence thinking, behaviour and mood.

Intestinal flora: healthy diversity, healthy human

Researchers are only just beginning to understand the complex interplay between humans and their intestinal flora. When it comes to your personal «relationship» with your tiny lodgers, the following fact is particularly important: your intestines are home to bacteria which can have a positive or negative effect on your health. It depends on the type of bacteria, but primarily on where they occur and in what relation to each other. This sometimes makes itself felt in an unpleasant way – for example in the form of gastrointestinal complaints.

People with Crohn’s disease or ulcerative colitis – where the variety of microbial co-inhabitants is limited – know this from painful experience. But even those who have had diarrhoea after taking antibiotics have experienced it first-hand. This is because so-called broad-spectrum antibiotics are usually used, which make no distinction between friend and foe when it comes to intestinal bacteria.

Tip from Professor Scharl: next time, get a prescription for a probiotic, such as saccharomyces boulardii, in addition to the antibiotics. They stabilise the microbiome and support regeneration of the intestinal flora.

Feeding your gut

But it’s not just medication that affects your microbiome. «For example, there are also indications that our Western diet – little fibre, lots of animal fat and sugar – combined with stress and lack of exercise reduces the variety of intestinal germs,» says Scharl. Flatulence, digestive problems and other issues are the lesser evil in this case.

At the same time, bacteria multiply that produce trimethylamine, a substance that’s suspected of increasing the risk of arteriosclerosis and thus heart attack and stroke. For the sake of your microbiome, you should therefore make sure you have a balanced diet rich in fibre and grains with lots of fresh fruit and vegetables and maintain a healthy, relaxed lifestyle.

Unfortunately, probiotics aren’t a convenient substitute. They can only be an addition. «It’s also important to know that there are three categories of probiotics,» says Michael Scharl. «There’s prescription medication that’s reimbursed by health insurance. Probiotic products from pharmacies and chemists have also often proven to be effective. However, you can’t specifically feed certain bacteria with them. In contrast, there’s usually no scientific evidence of the effectiveness of probiotic-enriched foods such as yoghurts or drinks. That said, if probiotic products work for you, you should take them.»

Gut microbiome changes: the cause or effect of many diseases?

You don’t actually need more knowledge and more action to live in healthy harmony with your microbes. Nevertheless, there’s currently huge hype about the biome. This is understandable from a scientific point of view: researchers are discovering something new almost every day. But, in addition to specialist articles and studies, numerous popular scientific bestseller guides such as the German book Darm mit Charme, which translates as Charming Bowels, are also springing up, which is obviously piquing the curiosity of the general public. And many succumb to the countless offers to get an insight into their intestines and therefore their state of health by means of a microbiome stool examination.

«Studies show that the microbiota of patients with certain diseases differs from that of healthy people,» confirms Scharl. And the list of diseases associated with a changed microbiome is a long one, ranging from chronic inflammatory bowel diseases to allergies, rheumatism, diabetes, obesity (morbid obesity), depression, autism and neurological diseases such as multiple sclerosis.

However, it’s far from clear whether changes in the microbiome trigger these diseases or whether they’re a consequence of them. It could be both. «In addition, not all people who show certain deviations suffer from the associated ailments or will go on to suffer from them,» emphasises Scharl.

Still healthy or already ill?

Michael Scharl is therefore rather reticent about self-tests. «Yes, they give correct results. But there’s currently a lack of correct classification of the findings and, if necessary, working out a treatment,» he says. Because the microbiome also differs from person to person, there’s still no definition of which bacterial values and compositions can be considered «normal» for a healthy person and whether and when exactly changes reliably indicate the development or progression of diseases.

«If you go to the doctor to have your liver values checked and they are too high, you have liver damage and you can look for the causes. This classification doesn’t exist for the microbiome, at least not yet,» says expert Scharl. People who have undergone tests and are unsure often end up with him at his microbiome consultation hours at the USZ (website in German) to discuss their results.

Microbiome in the gut: hope for the medicine of the future

However, the majority of people attending the consultation hours come to get help with gastrointestinal complaints or questions about stool transplants, where the prepared stool of a healthy person is transferred to an ill person. «The procedure is used in patients with antibiotic refractory Clostridium difficile colitis and is very successful. But this is the only situation where we perform it,» says Michael Scharl.

In the future, he believes that research into the microbiome can provide many more possibilities for even more targeted therapeutic interventions and microorganisms in the digestive tract will play a major role in medicine in the future as a therapeutic agent.

Scharl hopes that diseases can be cured by changing the composition of intestinal flora or by replacing the bacteria reduced by illness. «The ideal treatment would be if patients could be given individually tailored bacterial cocktails or isolated metabolites in tablet form.»

This could happen in two to three years in the field of colon cancer. In experiments with mice suffering from cancer, T cells that kill the tumour were activated by orally administering the bacteria that are reduced in the intestines of cancer patients.