Kaisa Kopliste: The gut is our second brain
There's bustling activity going on in your gut, with effects reaching further than we tend to realise. A growing body of research confirms that the microbiome plays a central role in how our immune system functions, in hormone balance, in regulating inflammatory processes, and even in shaping our mood.
It’s not for nothing that we rely on “gut feelings” for important decisions — you may have heard the gut described as a second brain. People falling in love can feel butterflies in their stomach, and the gut also signals when we’re anxious or afraid. Sometimes we describe feeling apprehensive as having a “cold stomach.”
There’s been growing discussion lately about the gut and the life teeming within it, since it’s a rapidly advancing field of research full of exciting discoveries. Many of the processes involved still aren’t fully understood, but the discoveries made so far already carry real significance for health, wellbeing, and lifespan. It’s fair to say that when our gut bacteria are doing poorly, so do we — and vice versa.
To keep things concrete rather than abstract, here are some specific examples of how gut bacteria can affect our everyday lives.
Energy levels: a diverse microbiome helps the body absorb nutrients more effectively and influences blood glucose levels, reducing energy fluctuations and fatigue. When inflammation-promoting bacteria dominate the gut, it can increase chronic stress in the body and contribute to feelings of fatigue.
Mood: around 95% of the body’s own serotonin and more than half of its dopamine are synthesised in the gut — produced both by our own gut cells and by the microbes living there. While these neurotransmitters don’t cross the blood-brain barrier, they influence mood through nerve, hormonal, and immune pathways: the gut-brain axis carries signals that help regulate stress tolerance, motivation, and a sense of wellbeing. A balanced microbiome therefore supports both serotonin and dopamine circulation, while an imbalance can contribute to anxiety, mood swings, and reduced motivation.
Cravings: microbes aren’t passive passengers. When a particular bacterial species starts running low on its food supply, it sends a signal to the brain to stimulate a craving for its favourite food. The more we eat certain foods, the larger the corresponding bacterial population grows. So if the gut is dominated by bacteria that have thrived on gummy sweets and chocolate, the craving for those foods isn’t purely down to us — the collective “willpower” of thousands of bacteria often turns out to be stronger than our own.
Or, if we eat cabbage soup, it’s a feast for the specific bacteria that feed on the fibre found in cabbage. Once those bacteria have had their fill, they send a signal to the brain: “That’s enough cabbage soup!” This happens within about 20 minutes — coincidentally, the same amount of time it typically takes to register a feeling of fullness.
In fairness, the mechanisms behind hunger and satiety are considerably more complex than described here — but when the microbial community is out of balance, or when we eat a lot of ultra-processed food (frozen pizza, instant noodles, brightly coloured breakfast cereals), appetite regulation gets thrown off.
Body weight: the gut microbiome of people who are overweight is generally less species-diverse, and tends to be dominated by bacteria that are particularly efficient at processing high-carbohydrate foods. Some carbohydrates can’t be digested by human digestive enzymes, but certain gut bacteria are able to break them down effectively, producing fatty acids from them. That’s not inherently bad — but when such bacteria are present in excess, they extract significantly more usable or storable energy from carbohydrates than would otherwise be available. Microbes also influence how much dietary fat reaches the bloodstream versus how much is excreted undigested. As a result, the amount of energy absorbed from the same amount of food can vary considerably from person to person.
So our wellbeing depends, in large part, on what we eat. Eating wisely improves energy levels, mood, and stress tolerance — and that also means fewer sick days, a stronger immune system, and even a more positive outlook on life. If navigating the world of foods, nutrients, and gut microbes feels overwhelming on your own, you can always turn to a nutritionist for help.
Since every person’s microbiome is as unique as a fingerprint, general recommendations don’t always suit everyone. That’s where a nutritionist can help — figuring out which foods and eating habits genuinely support your own physical and mental wellbeing.
