Dr. Martina Melzer, published: 10.04.2022


Deutsche Version



All diseases begin in the gut. This was already said by Hippocrates, who is considered the most famous physician of antiquity and the founder of scientifically oriented medicine. Do diseases that lead to chronic fatigue also begin in the gut? Who knows. There are indications that this is the case. At the very least, it plays a central role when it comes to our mental, emotional and physical well-being.

I could write a book about the gut. But I want to be as brief as possible here and only mention the aspects that I believe are important in the context of fatigue.

The intestinal immune system

The intestine not only digests our food. It fulfills many other tasks. For example, it houses 70 to 80 percent of all immune cells. This makes sense because many pathogens and other potentially harmful substances from the environment enter the gut. Before food components are absorbed from inside the intestine into the intestinal mucosa and make it from there into the portal circulation and ultimately into the bloodstream, they must be tested. Are the food components good, bad, useful or dangerous, welcome or not welcome, do they need to be killed? These decisions are made by the gut immune system - at every meal we eat.

That's why every meal also triggers a tiny inflammatory reaction in the gut that we normally don't notice. If there is a stronger or repeated inflammation, we do notice it. For example, as diarrhea, exhaustion, a flu-like feeling. If the intestine is constantly a little inflamed, it restricts digestive activity, can contribute to nutrient deficiencies and trigger fatigue. Inflammation can propagate through the body, affecting other organs, weakening mitochondria. These are our small, vital energy power plants. The formation of hormones can also change. For example, imbalances of thyroid hormones, sex hormones and stress hormones occur. All of this contributes to chronic fatigue and many other symptoms.

Inflammatory reactions in the gut can also cause inflammation in the brain. This probably happens via the vagus nerve, the calming part of our autonomic nervous system. It registers that something is wrong in the gut. Inflammatory messengers, called cytokines, and immune cells trigger the vagus. Tell it to watch out for danger, intruders, problems. The vagus nerve transmits the information to the brain, triggering, among other things, the so-called sickness behavior: We are exhausted, tired, want to lie down, may have a fever, aching limbs, are not in a good mood. Studies indicate that an intestinal inflammation is mirrored by the brain, so to speak, and that immune cells and cytokines are also released there. In addition, activated immune cells from the intestine can migrate into the central nervous system, which could possibly play a role in the development of multiple sclerosis.

If our immune system is somewhat out of balance, it sometimes can no longer distinguish between good and evil. A food component or pathogen may look similar on its surface to the body's own tissue. The immune cells directed against these surface components not only react to the foreign substance, but also attack the body's own tissue: an autoimmune reaction develops. In diseases such as celiac disease, ulcerative colitis, Crohn's disease, but also multiple sclerosis and rheumatoid arthritis, such processes play or could play an important role. If, on the other hand, the immune system is too weak or exhausted, one becomes more susceptible to infections.

The gut flora

The intestinal flora, also known as the intestinal microbiome, influences a wide variety of bodily functions. It consists of a large number of bacteria, but also of fungi, viruses, parasites and other single-celled organisms. There are very useful, helpful and for us indispensable microorganisms. They help to digest food, influence our mood and sleep, seal the intestinal wall against harmful microorganisms, form short-chain fatty acids as an energy substrate for the intestinal cells, produce brain messengers and have an anti-inflammatory effect.

In addition, there are intestinal inhabitants that tend to promote inflammation and can cause trouble if they multiply unintentionally. Then a dysbalance occurs that can lead to inflammation in the intestines and ultimately in the whole body. And that, of course, is accompanied by exhaustion.

A disturbed gut flora seems to play a role in many diseases, for example in autoimmune diseases, in ME/CFS, in fibromyalgia, depression, anxiety disorders, Parkinson's, etc.... At present, however, it is not yet possible to say exactly whether the altered intestinal flora is the cause or consequence of these diseases. Scientists have only been able to establish a connection.

The gut-brain axis and other axes

There is a lively exchange between the gut and the brain. The intestine has its own nervous system, the intestinal nervous system. Just like the autonomic nervous system, it also functions involuntarily. That is, without our being able to consciously influence it directly - only indirectly. Science is not yet in agreement as to whether the intestinal nervous system is an autonomous system in its own right or should be understood as part of the autonomic nervous system, which is made up of the activating part, the sympathetic nervous system, and the calming part, the parasympathetic nervous system.

The parasympathetic nervous system consists mainly of the vagus nerve. It originates in the brainstem and then travels down the throat along the esophagus through the heart, into the stomach, intestines and other abdominal organs. It and the gut nervous system are constantly communicating with each other - this is the gut-brain axis. The gut is an important feeler to the outside world. Food, toxins, pathogens, plastic particles, etc. enter it. But also our emotional world, our emotions have an effect there or maybe even originate there. The intestine produces important brain messengers, for example serotonin and dopamine, which also play an important role in the central nervous system and the limbic system (our emotional center). Ninety-five percent of the serotonin in the body is produced in the gut. The gut nervous system is a reflection of the central nervous system - or vice versa.

The vagus nerve gets everything that's going on in the gut. Whether the immune system is activated, the intestine (or we) are not in a good mood, the intestine senses danger. The vagus nerve hears this and passes the information on to the brain. 80 percent of the information that this nerve passes on comes from our gut. Only 20 percent it passes on from "upstairs downstairs." The gut and vagus affect our mood, behavior, actions, sense of illness, exhaustion, pain, and much more. You simply cannot underestimate the gut.

If the gut-brain axis is disturbed, it can lead to far-reaching problems in the body. Not only irritable bowel syndrome, but also inflammatory processes in the intestine, brain and other organs or tissues. The dysfunction also has an emotional impact: Some research groups suggest that depression and anxiety disorders may arise in the gut when the gut-brain axis is out of balance, as is the gut flora (see above).

That emotions are closely linked to the gastrointestinal tract is illustrated by phrases such as "my bile comes up," "I could puke, I'm so disgusted," "I have a lot to digest," or "love goes through the stomach." And the gut feeling, the sixth sense, is not nonsense, but is emblematic of the intestinal nervous system and the vagus. Mental or physical trauma upsets the gut nervous system and autonomic nervous system. The body is stuck in a perpetual stress response. It is on sympathetic continuous fire. The counterpart, the vagus, is blocked. However, there are other variations on this. For example, part of the vagus nerve may be too active, or the sympathetic and parasympathetic nerves may be stuck on "on" at the same time. This also explains why stress and trauma affect digestion so much.

IBS is now considered primarily a disorder of the gut-brain axis. Many people with ME/CFS, fibromyalgia, depression or irritable stomach have a parallel irritable bowel syndrome. What exactly lies behind the syndrome is not yet entirely clear. The intestinal nervous system, as well as the communication between the intestine and the brain are out of kilter, the intestinal flora is often altered, the intestinal barrier becomes more permeable and there are probably tiny inflammatory reactions in the intestine. However, as with ME/CFS, I am many. Not everyone has the same irritable bowel. According to the German physician guidelines, all the food intolerances that lead to irritable bowel symptoms are more of a differential diagnosis, i.e. they are to be distinguished from the "real" IBS.

In addition to the gut-brain axis, there are probably at least two other axes: the gut-heart axis and the gut-joint axis. If they get out of balance, this could have a negative effect on cardiovascular diseases and rheumatoid arthritis.

Leaky gut syndrome

I come across this term very often. One could speculate that with this syndrome the intestine becomes as full of holes as Swiss cheese. But of course this is not true. Rather, leaky gut is associated with increased permeability of the intestinal mucosa.

The intestinal mucosa is always permeable to some degree, otherwise we would not be able to absorb nutrients through it. But in some people and various medical conditions, the connections between intestinal cells are somewhat less dense. Therefore, larger molecules from food, pathogens or other origins also enter the mucosa and can trigger an inflammatory reaction there, depending on individual sensitivity. The intestinal immune system is activated and this can manifest itself with symptoms.

As is so often the case in science, opinions differ as to how far the consequences of a "leaky gut" can reach in the body. Some say: Does not exist. Others say: limited to the gut, with bloating, flatulence, diarrhea, constipation, bloating. Some researchers and investigators suggest that increased intestinal permeability may worsen the condition in diseases such as ME/CFS, MS or rheumatoid arthritis. And may also exacerbate symptoms such as headaches, joint pain and fatigue. It is also unclear whether the syndrome is a cause, consequence or concomitant. In contrast, a more permeable intestinal wall is clearly present in Crohn's disease and ulcerative colitis.

Food intolerances and allergies

During my own crazy research over the past few years, I've learned: you can be sensitive to all kinds of foods. Whether that's an intolerance or an allergy. And what you can tolerate or not is a highly individual thing.

There are people who react to gluten or amylase trypsin inhibitors from wheat, for example. Others get intestinal problems or discomfort elsewhere in the body if they eat too much lactose, fructose, sorbitol, histamine, oxalate, salicylates or FODMAPs (fermentable oligo-, di-, monosaccharides and polyols). However, dairy protein, soy, nuts, eggs, fish, celery, cabbage, legumes, grains and nightshade vegetables such as peppers and eggplant can also cause problems.

More on FODMAPs from the creator of the low FODMAP Diet:

Having had quite a bit of intestinal problems (and still having some), I went almost crazy with foods. I tried all kinds of diets, gave up a wide variety of foods, kept a diary. Spent an awful lot of money on intolerance tests that didn't help me much after all. I think some of you know this too. Ultimately, giving up dairy and wheat products helped me the most, eating FODMAPs in moderation and dosing foods too high in fiber well. And: reintroducing meat and drinking bone broth.

Unfortunately, as I said, it's very individual. That means you have to become a detective again and find out for yourself what you might not tolerate by abstaining for a limited time. Important: Don't avoid too much for too long. Our gut loves variety and the body gets all the important macro and micronutrients it needs from a wide variety of foods.

SIBO and Candida overgrowth

SIBO, or small bacterial overgrowth, has also become such a buzzword. It means that too many bacteria have settled in the back of the small intestine, which actually do not belong there to this extent. This can trigger a number of intestinal problems, exhaustion, as well as other ailments. As usual, it is controversial whether and how to treat the faulty colonization. With specific antibiotics or by temporarily avoiding carbohydrates? My message here is: If you have irritable bowel symptoms and nothing has helped so far, try to find a gastroenterologist who knows about SIBO and can test you. Then it can be discussed about the appropriate therapy.

The same applies to an overgrowth of Candida fungi in the colon. Yeast fungi are present in every healthy colon and are part of our normal intestinal flora. They are not bad per se. However, in some people, candida yeasts can multiply explosively, upsetting the intestinal flora, triggering inflammation and thus causing problems. This can be particularly dangerous for immunocompromised people. The best thing is to find a "smart" doctor who is familiar with this and then see what happens.

What is good for the gut

  • Eat the rainbow: As many colors as possible in the vegetable pan. The intestine loves variety, and strongly colored fruits and vegetables are particularly rich in useful secondary plant compounds. But also cabbage and green leafy vegetables should not be missing.
  • Eat as much unprocessed food as possible. Ideally, you can still recognize the basic food. Otherwise: preferably a maximum of five ingredients on the ingredient list.
  • Eat fermented foods like (vegan) yogurt, sauerkraut and kimchi. In it many lactic acid bacteria are found, which belong to the healthy intestinal flora. Whether probiotics in pill or powder form help varies again from person to person. I've tried a lot of them without significant success, but that doesn't have to be the case for you. If, then I would advise a preparation from the pharmacy that really contains many germs and a mixture of different. Probiotics, however, are a science in themselves.
  • Just as important as probiotics are prebiotics. These are ingredients in foods that serve as food for the good intestinal bacteria. For example, they love inulin, FODMAPs (which is why a permanent low FODMAP diet is not good from my perspective), and other special carbohydrates found in legumes and whole grains, for example.
  • Dietary fiber is important overall for intestinal health and digestion. Therefore, eat whole grains, legumes, lots of vegetables and some fruits, nuts, seeds regularly and according to individual tolerance. I myself have additionally experimented a lot with psyllium and flaxseed. Psyllium was nothing for me, but almost ground flaxseed was, and more recently acacia fiber powder.
  • Fasting and intermittent fasting are good for the intestines, because then they have time to clean themselves, reject old cells and form new ones. However, it is not suitable for everyone.
  • Sleep is important for good digestion.
  • Daily relaxation, rest, a nap, yoga, meditating, stretching the stomach once in a while - it likes that.
  • In some cases, glutamine can help rebuild a damaged intestinal lining. The amino acid is in bone broth, for example. It's helped me a lot, even though I'm not actually that excited about it. Organic is important here.

What harms the gut

  • Pesticides and other chemicals, plastic particles
  • Too many highly processed foods such as flour, pasta, pizza, sodas, sausage, etc.
  • Emulsifiers from processed foods
  • A diet that is too restricted, with too many foods being avoided
  • A lack of fiber and prebiotics
  • Stress and lack of sleep the intestine does not like at all
  • Too frequent use of antibiotics
  • Many drugs affect the gut and change the intestinal flora in the long run
  • Too much sport stresses it and disturbs the digestive function
  • Alcohol, ingredients from cigarettes, sugar
  • Sorrow and worries, suppressed emotions

I have focused on the gut here because it has so many influences on us. But of course, stomach problems, impaired liver, gall bladder or pancreas function can also be accompanied by fatigue and other symptoms.


PS: Of course, I research and check everything I write here as well as possible. Nevertheless, I am only human and make mistakes. In addition, I may draw completely different conclusions as someone else would. Simply because they fit my story. But every story is different.

Important: The content on this page is for informational purposes only and is not a substitute for talking to your doctor or other therapist. The content reflects my personal experiences, research and findings that have helped me and that I therefore want to share. However, in your personal case, completely different things may play a role and other things may help. Please talk to your doctor or therapist before making any decisions that affect your physical or mental health. Also important: I don't want to convince anyone of anything here. Rather, I want to point out possible ways that hopefully can help some people to improve or overcome their Fatigue or ME/CFS.



Fatigue Super Conference 2021

Prof. Georg Hasler: Die Darm-Hirn-Connection

Zaiss MM et al: The gut–joint axis in rheumatoid arthritis. Rheumatology 2021

Sofia K. Forslund: Combinatorial, additive and dose-dependent drug microbiome associations. Nature 2021

Ghali, A., Richa, P., Lacout, C. et al. Epidemiological and clinical factors associated with post-exertional malaise severity in patients with myalgic encephalomyelitis/chronic fatigue syndrome. J Transl Med 2020

Dr. Anne Fleck: Energy

Prof. Martin Storr: Sofortratgeber Leaky Gut

Simpson CA, Diaz-Arteche C, Eliby D, Schwartz OS, Simmons JG, Cowan CSM. The gut microbiota in anxiety and depression - A systematic review. Clin Psychol Rev. 2021

Dr. Terry Wahls: MS erfolgreich behandeln

Podcast: Unbiased Science – Leaky gut misconceptions

Update S3-Leitlinie Reizdarmsyndrom: Definition, Pathophysiologie, Diagnostik und Therapie des Reizdarmsyndroms der Deutschen Gesellschaft für Gastroenterologie, Verdauungs- und Stoffwechselkrankheiten (DGVS) und der Deutschen Gesellschaft für Neurogastroenterologie und Motilität (DGNM) 2021

Detlef Schuppan, Kristin Gisbert-Schuppan: Tägliches Brot – Krank durch Weizen, Gluten und ATI