Between 2007 and 2018, while I was serving as a psychiatrist at Harvard University and then at Smith College, my seasoned colleagues and I observed a most disturbing trend: It was becoming increasingly common for first-year students to arrive on campus already taking one, two, or even three psychiatric medications. Requests for specialized support for learning and emotional disabilities were rising so fast that it was difficult to accommodate everyone’s needs. More and more students were showing up at campus mental health clinics in crisis, requiring emergency psychiatric hospitalizations, leaves of absence, or academic withdrawals. The sense among clinicians on the front lines is that the mental health of our young people is increasingly brittle, and research supports our observations.

While ... physical and mental health conditions may seem unrelated to each other, they commonly occur together and share many of the same underlying abnormalities, the most important being inflammation, oxidative stress, and insulin resistance.24

Inflammation and oxidative stress are part of your immune system’s first responder network, so it is normal and healthy to have a certain degree of both, but excessive inflammation and oxidative stress can be very damaging to every cell in the body—and brain cells are no exception.

Insulin resistance (which is often called “prediabetes”) is a common metabolic disorder in which insulin doesn’t work as well as it should. If you have insulin resistance, your body will need to produce more than the usual amount of insulin to try to keep your blood sugar (and brain sugar) levels stable and in a healthy range, so your insulin levels will tend to run too high. Over time, high insulin levels can make it more difficult for your brain to turn glucose (blood sugar) into energy.

It just so happens that our industrially ultraprocessed diet is a powerful promoter of inflammation, oxidative stress, and insulin resistance—all of which are just as dangerous for the brain as they are for the rest of the body. In the long search for biological root causes of mental illness—a search that has been focused almost exclusively on neurotransmitters for nearly seventy-five years—inflammation, oxidative stress, and insulin resistance have emerged as an unholy trinity of destructive forces that help to explain why those neurotransmitter imbalances occur.

We readily accept that diet plays a major role in the health of the rest of the body—why should the brain be any different? The foods we eat provide the construction materials we need to build healthy, resilient brain cells and the fuel we need to energize them. If we don’t eat the right foods, none of our cells will develop or function properly, and any number of things can and will go wrong—including many things no medication can address.

Medications can and do change brain chemistry, and they have their place, but I’m convinced that the most powerful way to change brain chemistry is through food, because that’s where brain chemicals come from in the first place. Neurotransmitters are made from food, the brain cells that pass them back and forth to communicate with each other are made from food, and even the salty soup that surrounds them is made from food. Optimal mental health requires that your whole brain be made of the right stuff, so if you have a mental (or physical) health problem of any kind, the first place to look isn’t your medicine cabinet, it’s your pantry. This advice holds true whether you view mental health conditions as primarily biologically driven or psychosocially driven, because, as we’ll see in the coming chapters, the way we eat has a profound impact on brain development, neurotransmitters, stress hormones, inflammation, antioxidant capacity, brain energy production, brain aging, and brain healing.

There is only so much you can do to reduce your exposure to stress, and nothing you can do to change the genes you were born with or the childhood you experienced, but you can change your diet—and changing your diet can change your mind.