"Who eats first?" Richard asks Dr. Emeran Mayer as the researcher discusses his new book about the gut-immune connection. The answer is as complex as gut health and immune system interactions, but also just as fascinating.

Listen and learn:

• How the rapid timeline of microbiome research led to understanding connections between gut microbiota and immunity,
• How facial expressions from emotions are also happening, in a sense, in the gut,
• How your brain monitors what's happening in your gut through the gut-immune connection, and
• What hormones are released in your gut and how those tie to emotional reactions.

Dr. Emeran Mayer's discusses his latest book, The Gut-Immune Connection: How Understanding the Connection Between Food and Immunity Can Help Us Regain Our Health. He digs deep on some of this timely book's topics, including the ties between our emotions and gut processes.

The trillions of microbes producing their own chemicals, or metabolites make for quite a "bi-directional dialogue," he explains. Neurotransmitters throw another element into the mix and the food we bring in completes this intense conversation between our gut and brain.

Who does eat first? Well, it's not a one-answer question, explains Dr. Mayer, because different microbes eat different foods. "With a typical standard American diet," he says, "most of it would be absorbed in that very beginning of the small intestine, because everything is processed with very little fiber . . . but if you eat a diet like our ancestors used to eat . . . much higher in fiber . . .  it has to travel down." And, it turns out, which microbes get fed the most affects how our body responds, and ultimately, our health. Listen in for more about this integral and fundamental connection.

Episode also available on Apple Podcasts: apple.co/30PvU9C