At the turn of the 20th century, prominent physicians who were trying to understand where mental illness comes from seized on a new theory: autointoxication. Intestinal microbes, these doctors suggested, are actually dangerous to their human hosts. They have a way of inducing “fatigue, melancholia, and the neuroses,” as a historical article in the journal Gut Pathogens recounts.
“The control of man’s diet is readily accomplished, but mastery over his intestinal bacterial flora is not,” wrote a doctor named Bond Stow in the Medical Record Journal of Medicine and Surgery in 1914. “The innumerable examples of autointoxication that one sees in his daily walks in life is proof thereof … malaise, total lack of ambition so that every effort in life is a burden, mental depression often bordering upon melancholia.”
In a recently released abstract, researchers studying 964 elderly participants over six and a half years found those who followed the DASH diet, which emphasizes whole grains, fruits, and vegetables, had lower rates of depression, while those who ate a traditional Western diet were more prone to depression. The participants were asked how often they ate various foods, and they were screened for depression annually using a questionnaire.
The research will be presented at the upcoming meeting of the American Academy of Neurology. The study has not been published yet in a peer-reviewed journal, but other researchers have found similar antidepression benefits from the DASH diet, which was developed by the U.S. National Heart, Lung, and Blood Institute.
Of course, rich people tend to be happier and can afford to eat better. Cherian’s study did not control for socioeconomic status. But overall, the evidence suggests diet improves depression symptoms even when controlling for factors like income or education, says Felice Jacka, a professor of nutritional psychiatry at Australia’s Deakin University.
The DASH diet itself is nothing revolutionary—a typical dinner consists of a lean meat, baked potato, and lots of vegetables. Researchers are still figuring out why it’s so beneficial, but a major pathway might be through the gut-brain connection. When people eat a plant-heavy diet, the fiber from the plant matter ferments in the gut and creates short-chain fatty acids, which, in turn, regulate the immune system and influence gene expression in the brain and elsewhere. People who eat fiber have more diverse gut bacteria, and these bacteria make various chemicals that influence our mood.
Cryan says these studies point to the growing recognition of the importance of diet—along with the other old standbys, exercise and sleep—in regulating mood. In fact, despite feeling cautious about the early nature of this line of research, he says he would recommend depressed people try eating better to see if it helps.
