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Introduction

The causes of disease often lie elsewhere than where we initially look for them in everyday life, namely directly at the symptom. Many complaints appear to be isolated disorders, but are in fact the end result of a longer chain of events: stress, sleep deprivation, an unbalanced diet, recurring inflammatory stimuli, and silent deficiencies can build up over months or even years. The book “If only patients knew: True causes, effective therapies” clearly presents this perspective: Those who only alleviate what hurts at the moment often overlook the reason why the body is sounding the alarm in the first place.

To avoid this remaining abstract, the book deliberately goes into depth: what makes the microbiome so relevant, how does gut-brain communication work, why can a nutrient deficiency upset the psyche, and where in everyday life are the causes of disease systematically overlooked?

Why symptoms rarely tell the whole story

A symptom is often a signal and not the core of the problem. Abdominal pain can be caused by an acute infection, but also by prolonged stress, altered intestinal flora, disturbed sleep patterns, or a diet that constantly irritates the intestines. The same applies to psychological complaints: irritability, listlessness, or anxiety do not have to be explained solely in psychological terms. They can also be exacerbated by inflammatory processes, hormonal shifts, or micronutrient deficiencies.

The crux of the matter is that symptoms are visible, but causes are often invisible. Those who focus exclusively on the visible symptoms have a good chance of short-term relief, but a poorer chance of stable improvement. This is precisely where addressing the causes becomes relevant.

Causes of diseases in the microbiome: What is considered certain today

The microbiome is not a fad, but an independent biological system. An unimaginable number of microorganisms live in the intestine, producing metabolic products, training the immune system, and influencing the intestinal barrier. The current state of research shows quite clearly that it is not a single “good” bacterium that makes us healthy, but diversity, balance, and function.

Important mechanisms that are well described today:

  1. Metabolic products
  2. Bacteria convert fiber into short-chain fatty acids. These substances have an anti-inflammatory effect in the intestine and can also trigger effects outside the intestine via the blood and signaling cascades.
  3. Intestinal barrier
  4. When the barrier is weakened, bacterial components can enter the body more easily. This increases the likelihood of low-grade, persistent inflammatory activity.
  5. Immune system
  6. A large part of immune activity is located around the intestine. Disturbed intestinal flora can shift immune responses and increase susceptibility to inflammation.

When this system is disrupted, it is often referred to as dysbiosis. And this is where it gets practical: dysbiosis does not necessarily cause immediate dramatic intestinal problems. It can also manifest itself indirectly, for example through fatigue, recurring infections, skin problems, or increased susceptibility to stress. These are typical situations in which the causes of illness are easily overlooked because the intestines are examined too late.

Gut-brain communication: Why your gut influences your mood

The gut-brain connection works in several ways simultaneously. One of the main ones is the vagus nerve, which transmits information from the abdomen to the brain. Hormone signals, immune messengers, and metabolic products also play a role. The direction is important: it works both ways.

What does that mean in everyday life?

  • Psychological pressure can change digestion
  • Many people are familiar with this: nervousness, queasy stomach, sudden urge to go to the bathroom. This is not imagination, but biology.
  • The condition of the gut can increase feelings of stress
  • When inflammation and barrier problems increase, physical alertness often rises. People often describe this as “constantly tense,” even if nothing is objectively happening at the moment.
  • Neurotransmitters are not just a matter of the mind
  • A large part of serotonin is produced in the intestinal area. This does not mean that the gut “causes” depression. However, it does mean that the condition of the gut and neurotransmitter balance are linked.

Recent reviews also emphasize that the interaction between the microbiome, nerve pathways, and immune responses is complex. This is precisely why there is rarely a single adjustment screw. Nevertheless, it is worth taking a look, because the causes of diseases often become visible here earlier than in blood tests.

Causes of stress-related illnesses: When the system no longer shuts down

Stress is not just a feeling, but physiology. For many people, constant stress increases their basic inner tension, affects their sleep, changes their eating habits, and can alter their metabolism and immune system via stress hormones. This particularly affects the gut, because intestinal movement, blood flow, and immune activity are sensitive there.

A typical course looks like this:

  1. High pressure over weeks
  2. Sleep deteriorates, cravings increase
  3. Diet becomes more unbalanced, alcohol or sugar are consumed more frequently
  4. Intestinal flora changes, susceptibility to inflammation increases
  5. Mood becomes more unstable, concentration decreases
  6. Complaints become “chronic” because there is no longer any real recovery

This is often one of the central causes of diseases of our time: not a dramatic event, but a lack of regeneration. Those who only treat the surface overlook the permanent overload mode.

The psyche due to deficiency: Why nutrients are so important for mental health

When people hear “nutrient deficiency,” many first think of bones, muscles, or blood. The brain is forgotten, even though it constantly needs energy and building materials. Several micronutrients are necessary for the formation and regulation of neurotransmitters, i.e., precisely those processes that shape mood, sleep, and drive.

Particularly frequently discussed and repeatedly relevant in studies:

  • Vitamin B12
  • Important for nerve function and blood formation. Low levels are associated with exhaustion, concentration problems, and low mood in some affected individuals.
  • Vitamin D
  • Associated with immune regulation and mood in many studies. At the same time, the results on the direct effect on depression are not always clear. Conclusion: Recognize deficiencies and compensate for them sensibly, do not blindly administer high doses.
  • Magnesium
  • Involved in many reactions in the nervous system. Some people react to a deficiency with inner restlessness, sleep problems, or increased stress reactivity.
  • Omega-3 fatty acids
  • Important for cell membranes, including in the brain. Meta-analyses show small to moderate effects on depressive symptoms, depending on the initial situation, especially as a supplement, not as a substitute.
  • Iron
  • A deficiency can increase fatigue, reduce performance, and thus indirectly increase psychological stress.

The key point: A deficiency is rarely the only cause, but it can stabilize symptoms and weaken therapies. Anyone who takes the causes of disease seriously therefore examines not only the psyche, but also the physical conditions of the psyche.

Recognizing the causes of disease: nutrition, fiber, and targeted support

If gut flora and nutrients are so important, the path almost automatically leads to nutrition. Not as an ideology, but as daily input for metabolism and the microbiome. The idea of diversity is particularly convincing: the more varied the plant-based foods, the more different bacteria are fed, and the more stable the system often becomes.

Practical principles that are reflected in many recommendations:

  1. More fiber, increase slowly
  2. Legumes, vegetables, nuts, seeds, whole grains. Fiber is the staple food of many beneficial bacteria.
  3. Reduce ultra-processed products
  4. Don’t “ban everything,” but clearly reduce the proportion. Many people notice differences in energy and digestion after just a few weeks.
  5. Don’t forget protein and healthy fats
  6. Stable blood sugar curves also help mentally. Extreme fluctuations can increase nervousness and irritability.
  7. Try fermented foods
  8. Yogurt, kefir, sauerkraut, kimchi. Not everyone can tolerate everything, but it is often worth testing carefully.

And what about probiotics? Recent studies show that probiotics can measurably improve depressive or anxious symptoms in some people, especially when taken in sufficient doses and over a longer period of time. At the same time, the results are not the same for everyone, because the initial situation, bacterial strain, and lifestyle strongly influence the effect. In practice, this means that probiotics can be a building block, but they do not replace work on nutrition, sleep, and stress.

Regarding dietary supplements in general: Prophylactic use “for everyone” is not scientifically sound. Targeted supplementation makes sense in cases of proven deficiency or plausible undersupply, for example, vitamin B12 in vegan diets or vitamin D in cases of very little sun exposure. Anyone who wants to seriously address the causes of disease should rely on diagnostics, not hope.

Conclusion: The causes of disease often lie between the gut and everyday life

Many people look for the one trigger that explains everything. In reality, the causes of disease are often a bundle: a microbiome that has lost its balance, stress that no longer subsides, sleep that is too short, and deficiencies that make the nervous system vulnerable. This is not a moral judgment, but a functional model.

If you want to become more stable in the long term, you can focus on three questions:

  1. What keeps my system in a constant state of alarm?
  2. What is my body lacking that prevents it from regulating itself?
  3. What feeds my microbiome so that it becomes robust again?

If these questions become part of your health routine, you increase your chances of not only managing symptoms, but also truly changing the causes of illness.

Scientific reviews on the gut-brain axis and microbiome ⋅ Psyche

Recent studies and reviews (2024-2025)

Thematic articles & popular science explanations

Medically sound background information

Published on: 21. December 2025

Daniel

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Causes of diseases chronic diseases gut-brain axis holistic medicine Intestinal flora Intestinal health Mental health microbiome Mind and body nutrient deficiency Nutrition and health prevention Probiotics Stress and health vitamin deficiency