Your diet may affect your mental health.
Credit: Evgeny Kuklev / Getty Images

Thirty years ago neuroscientist Michael Crawford predicted that the rise of heart disease in the West would be followed by a corresponding spike in mental illness. His theory: That the nutrients needed for a healthy heart were the same ones required for a healthy mind – and that our ever fattier and more processed diet would be as disastrous for our brains as for our arteries.

Unfortunately, it looks as if he was right. In the United States, rates of depression, Alzheimer's, schizophrenia, and ADHD are all soaring. Yet the medical establishment is only now accepting that diet can impact mental health. "I would say that the fields of cardiovascular disease and cancer are about 20 to 30 years ahead of psychiatry in understanding nutrition," says Dr. Joseph R. Hibbeln, a lead clinical investigator at the National Institutes of Health.

Your diet can both change the way your brain functions and alter the structure of the organ itself. To produce the neurotransmitters that carry signals between neurons, your brain needs chemicals found in dark green leafy vegetables, fresh fruit, whole grains, and fish: omega-3 fatty acids, vitamin A, vitamin C, B vitamins, magnesium, folate, iron, zinc, and selenium, none of which your body can produce on its own. A diet poor in these nutrients can actually impair your brain's functioning.

Now consider what fat can do to your brain – it already makes up 60 percent of the organ's mass. And unlike carbohydrates and protein, which are converted during digestion, the fat you ingest shows up in your cellular membranes. Eat a lot of saturated fat and your brain cells will soak it up, becoming more rigid and therefore less able to do their various jobs.

Good fats, on the other hand, are essential. For instance, brain synapses rely on an important omega-3 fatty acid called docosahexaenoic acid (DHA), which is found in fish. DHA helps neurons fire, regulates the expression of genes, and influences the life and death of neurons themselves. There's also evidence that omega-3s can help fight stress.

The kinds of omega-3s found in fish also fight inflammation – which is a good thing, because research suggests that inflammation might contribute to mental problems ranging from depression to Alzheimer's. Omega-6 fatty acids, on the other hand, actually cause inflammation. That's okay when the two fats are in balance in the body, but our diets have changed so much over the past 100 years – with such a tilt toward omega-6-heavy foods like corn and soybean oils and corn-fed meat – that our current omega-6 to omega-3 ratio hovers closer to 10 to 1. An imbalanced fatty-acid ratio might even change behavior and mood for the worse. One study found a 30-fold decrease in homicide rates in cultures where seafood is a foundation of the diet.

No one believes poor nutrition is entirely responsible for mental problems. But more and more research shows that what we eat shapes our minds the way soil influences a tree. "If the soil is poor and there are no nutrients for the tree, the tree's growth is stunted," Hibbeln says. "It's still there, but it's just not as healthy."