This isn't some bullshit. There is a real science behind it.

Stanford University is one of the best research universities in the world.

When it comes to our mental state and the ability to manage stress, the brain is often the first suspect. However, our nutrition can also play a significant part in that the trillions of microbes living in our gut, known as our microbiome, hold significant sway over our daily emotions and long-term mental health. This is because our microbiome and brain are in constant communication, influencing one another’s next move via the gut-brain axis.

“Our gut can be thought of as having its own brain, replete with motor neurons, sensory neurons, and neurotransmitters. In fact, our ‘gut brain’ contains more of some neurotransmitters, like serotonin, than the brain in our head,” states Dr. Spencer.

“Increasing evidence is showing that bacteria in the gut, and the byproducts they produce, affect mood, cognition, and behavior,” states Dr. Spencer.

Our nutritional choices play a crucial role in shaping the composition and functionality of our gut microbiota. Consuming healthy foods fosters an environment where “good” microbes thrive, producing byproducts that benefit our mental health

https://lifestylemedicine.stanford.edu/stress-and-the-microbiome/

Eat a ton of fruits and vegetables. It will help your mood.