In recent years social media has been flooded with advice that "happiness is made in the gut" and that if you just feed the right bacteria in your intestines, depression will melt away on its own. It sounds nice. The problem is that, according to nutritionist Tamara Pazos, it's also wrong - at least in the part everyone leaves out.

It's true that around 90 percent of the body's serotonin is produced precisely in the gut. But, as Pazos explains, that gut serotonin doesn't reach the brain under normal conditions. "The body produces a large amount of serotonin in the gut, but it doesn't reach the brain. We can't claim that the microbiota makes serotonin, and that's why we feel happy," she says. The brain creates its own serotonin, using tryptophan - an amino acid we take in through food.

Here comes the truly useful part. Poor diet and chronic stress trigger something experts call "tryptophan grabbing" - an enzyme diverts that important ingredient away from serotonin production, which can then show up in mood and in mental clarity. So the gut-brain link does exist, it's just not as romantic as the influencers sell it.

What actually helps? Pazos recommends simple, undramatic things: fibre-rich food and a variety of vegetables, oily fish, walnuts, olive oil and pure cocoa, regular sleep, physical activity and reasonable stress management. Antibiotics only when they're really needed. None of this is an expensive supplement in a starry package - and that's exactly why it's rarely called a "revolution." Real care for your health is usually boring, cheap and without a hashtag.