About 90% of your body's serotonin is made in your gut, not your brain

Gut serotonin doesn't simply travel up to the brain; it mostly works in the gut itself, controlling how food moves through. But the gut and the brain are in constant conversation. The gut has its own network of around 500 million nerve cells, sometimes called the "second brain", connected to the brain through the long vagus nerve and through the immune system. It is why nerves give you "butterflies" and why stress can bring on stomach trouble.

Research on this gut-brain link is still young, but it is moving fast. Studies have found differences in gut bacteria in people with depression, and a well-known trial in Australia found that people with moderate to severe depression who improved their diet for 12 weeks, eating more vegetables, whole grains, legumes and less processed food, had a greater improvement in mood than those who were given social support alone.

Feeding the gut well - Eat a wide variety of plants each week: dals, beans, whole grains, vegetables, fruit, nuts, seeds. Fibre feeds good gut bacteria. - Homemade curd, chaas, idli, dosa batter and kanji are traditional fermented foods. - Go easy on heavily processed and fried food. - A change in diet can help mood, but it is not a replacement for treatment of depression. Use both.

Where this comes from - Yano JM et al. Indigenous Bacteria from the Gut Microbiota Regulate Host Serotonin Biosynthesis. Cell, 2015. - Jacka FN et al. A randomised controlled trial of dietary improvement for adults with major depression (the SMILES trial). BMC Medicine, 2017.