The phrase “mind-body connection” betrays a long tradition of believing our minds exist outside our bodies. In fact, your mind is your experience of your brain, a part of your body. Your brain gets a steady stream of information from your intestinal tract, where you digest food.
Many foods, for example, are high in the amino acid tryptophan, including soy, cocoa powder, cashews, chicken breast, oats, and eggs. Evidence suggests that higher — but not the very highest — levels of tryptophan in the blood improve thinking and probably mood. One 2014 study even found that taking a tryptophan supplement made people more willing to give to charity. (Maybe fundraisers should be sending us tryptophan pills instead of mailing labels.)
But tryptophan has to compete with other amino acids to reach your brain, which limits how much we normally get in food. To see the full effects, in one double-blind study, researchers designed a drink formulated so the tryptophan had unusually quick access to the brain. They then served it to group of healthy young women who were hooked up to brain scans. With just one serving, the scans recorded desirable changes in their mental processing.
Why might that be? Tryptophan converts in your body to serotonin — the brain chemical targeted in the most popular anti-depressant drugs, selective serotonin reuptake inhibitors. You may be surprised to hear that 95 percent of the serotonin in your body is in your gastrointestinal tract and that the gut actually contains more neurons than the spinal cord. Some people refer to those neurons as a “second brain.” It’s more important than we thought: Scientists were surprised to learn that the vast majority of the fibers in the vagus nerve at the base of the skull — the entryway to the brain — carries information from the gut to the brain rather than the other way around.
The gut is home as well to tens of trillions of bacteria, which communicate with those neurons in still-mysterious ways. Your diet affects which bacteria flourish in your gut. In turn, much evidence suggests that the balance of gut bacteria affects mood: for example, mice fed a high-fat diet did worse on tests of their memory and showed signs of “depression-like” behavior, along with observable changes in their gut bacteria. An imbalance in gut bacteria can lead to chronic low-grade inflammation, an immune reaction, and a slowing down in the production of new brain cells — both tied to depression. You might say that the wrong diet makes your body behave almost as if it were fighting an infection, which drags down your mood.
Our favorite feel-good foods have emerged from centuries in which human beings tinkered with plants to enhance chemical properties we favor. Studies have now backed up what millions of people know: dark chocolate and coffee boost mood. There’s also research on the way that fats in “comfort food” trigger signals from the gut to the brain that comfort us. Other scientists are exploring the similarities between obesity and addiction, in which vulnerable people become increasingly attached to the emotional rewards triggered by a food or drug.
So how can you know which foods will make you feel the best? The best advice may be to pay attention, since people vary. Good health feels good, too. Researchers who study the gut say it could be helpful to eat foods considered “probiotics,” such as yogurt and natural sauerkraut, and more vegetables. Eat to maintain your health, and use food as a mood-booster sparingly. After a particularly tough day, a hot chocolate sundae could definitely help, but over time cutting out sugar and upping your vegetables could make you feel far better.
March 20, 2015
Christopher Nystuen, MD, MBA