In the last few years, research to say that the gut does much more than just digest has been stacking up. We know that what we know about the gut flora – the microbiome – is only scratching the surface so far, more research is being carried out as we speak and new papers on the subject are published every week. Gut bacteria affect whether we are healthy or sick, slim or overweight, and it is more and more looking like they even have a say in who we are: The right bacteria may make us smarter, happier and more content, the wrong ones sad, depressed and anxious.
People’s wisdom has known about the connection between the gut and brain for a long time. We get a ‘gut feeling’ that something isn’t right. When we’re in love, we feel ‘butterflies in the stomach’, when we are scared we say that we are ‘shi**ing ourselves’ or are ‘sick to our stomach’. Fear of an exam, an interview or a performance can ruin our appetite and make our stomachs feel clenched. We are using our gut brain’s intelligence every day and call it intuition. Something we are less aware of is the fact that the gut might also be responsible for depression and anxiety or affect our resilience to stress. While for a long time conditions such as ADHD and autism were a mystery, we now know that at least part of the problem is rooted in the gut. Many IBS (irritable bowel syndrome) patients suffer not just from digestive problems, but also experience depression and doctors have noticed that sometimes antidepressants settle these patients’ guts or – the other way around – when their gut health improves their depression subsides. What’s more, serious brain diseases such as Alzheimer’s, Parkinson’s or multiple sclerosis (MS) seem to have a gut connection, too, and this opens up a whole new perspective on the treatment and management of those conditions. Researchers now know that our mood and even intelligence is much more affected by the health of our gut and the state of our microbiome than previously thought.
The gut and brain are connected in at least three different ways:
- The direct link between brain and gut: the vagus nerve
- Immune cells that were ‘trained’ in the gut travel to the brain via the blood stream. They act as mediators between the brain and the gut flora.
- Chemical messengers made by gut bacteria can make us feel anxious.
Many experts now refer to the gut as “the second brain” and while you wouldn’t think it to look at them: the two have a lot in common. For starters, the nerve cells of both gut and brain develop from the same tissue: during early pregnancy, part of the tissue that is going to turn into nerve cells moves to the head to become the brain, another part moves to the tummy to turn into the gut. Just like brain cells, gut nerve cells are support by glial cells.
The brain is protected by the blood-brain-barrier, a membrane that stops toxins, microbes or food allergens from entering the brain. Experiments with mice have shown that a healthy blood-brain-barrier depends on a healthy gut flora.
Just like our skin, the gut is in touch with the outside world, because – think about it – nothing is really inside our body until we have absorbed it! Bacteria, moulds, yeasts, toxins, parasites and allergens may enter the gut through our mouths, but for many of them the journey ends right there: stomach acid is the first obstacle, and what gets through there will next encounter gut immune cells and good bacteria. Gut defences protect our body and the brain from intruders and, moreover, the gut lets the brain know what’s going on. Only on a need-to-know basis though, it won’t bother the brain with everything that’s happening down below.
The gut is not called “the second brain” for nothing: It can even make its own decisions, without involving the brain. It does its job without instruction from the brain, can process a lot of information by itself and communicates with the body and brain. The gut is the only organ in our body that does not require regulation from the brain.
Bearing all this in mind, it is little wonder that gut health means brain health.