Your gut is often called the body’s ‘second brain’ because it has its own complex nervous system called the enteric nervous system (ENS), which contains nearly 100 million nerve cells—almost as many as the spinal cord. This system works independently and constantly communicates with your real brain. That’s why when you feel stress, anxiety, fear, or happiness, your stomach reacts instantly—like butterflies in the stomach, nausea, or hunger loss.
A major reason the gut influences your mood is that it produces about 90% of the serotonin in your body—the hormone responsible for happiness, calmness, and emotional balance. If your gut is healthy, serotonin levels remain stable, keeping your mood positive. But an unhealthy gut—due to poor diet, junk food, lack of sleep, or infections—can reduce serotonin production and trigger mood swings, irritation, anxiety, or even depression-like feelings.
Inside your gut lives a huge community of trillions of bacteria, known as the gut microbiome. These bacteria help digest food, absorb nutrients, and support immunity. But their role doesn’t stop there—they also send chemical signals to your brain through the gut–brain axis. When good bacteria are dominant, digestion becomes smooth, inflammation stays low, and your brain receives positive signals, improving your mental clarity, focus, and emotional stability. However, if harmful bacteria grow more, they release toxins and chemicals that can disturb brain signals, increasing stress and affecting your mood negatively.
Digestion also determines how your body handles stress. When food is digested properly, your body gets the right nutrients to make neurotransmitters like serotonin, dopamine, and GABA, which help regulate mood, sleep, and relaxation. Poor digestion means fewer nutrients reach the brain, making it harder for your mind to stay calm and balanced.
So the reason the gut is called the ‘second brain’ is because it not only controls digestion but also has a powerful influence on your emotional state, mental health, stress levels, and overall mood. Keeping your gut healthy with fibre-rich foods, probiotics, water, regular sleep, and low stress can directly help you feel happier and calmer from the inside out.
