Treating Depression with Diet

Michael Greger (0:00)

We have lots of choices to make about our diet. Add to that doing the right thing when it comes to treating a chronic disease, fighting a virus, or losing weight. And suddenly, our nutrition choices can seem almost overwhelming. Well, I'm here to help. Welcome to the Nutrition Facts Podcast. I'm your host, Dr. Michael Greger. Today we look at how plant-based nutrition may play a role in alleviating symptoms of depression. And, in our first story, we ask, do vegetarians have more or less depression and anxiety? Mental illness is among the leading causes of disability. Pharmacotherapy and psychotherapy, such as antidepressants and cognitive behavioral therapy, are cornerstones of treatment. However, they avert less than half of the disease burden, suggesting that additional strategies to prevent and treat mental disorders are needed. A new field of nutritional psychiatry provides evidence that diet quality has a modifiable risk factor for mental illnesses.

Cited mechanisms include chronic low-grade inflammation that's been implicated in the development of depression, schizophrenia and bipolar disorder, oxidative stress, free radicals may also be relevant to mental illness. And then there's compelling evidence, though predominantly from animal studies, indicating the gut microbiome can affect the brain. What kind of compelling evidence? Fecal transplant studies found that feeding rats feces from depressed people induces depression-like behavior.

Now, if I got force-fed feces every day, I might be depressed too, but rats fed feces from non-depressed people didn't act as depressed.

How might we sow the seeds of good mental health through our microbiome? Dietary factors that help our good gut bugs include more Mediterranean, more plant-based fruits and vegetables, fermented foods, nuts, fiber, and other prebiotics, plant-based proteins, predominantly plant-based fats, and polyphenols, which are also plant-based components. Bad for our microbiome is the Western diet, animal protein, saturated fat, which is concentrated in meat, dairy, and junk, and sweeteners and emulsifiers, which may help explain why greater ultra-processed food intake is associated with increased risk of subsequent depression. And the animal protein and animal fat may help explain why greater meat consumption is also associated with a higher risk of depression. So if plants may be good and meat bad, then vegetarians must be feeling great. But some compilations of studies found that vegetarians tend to show higher depression scores than non-vegetarians, and not just reviews funded by the National Academians Beef Association. Other systematic reviews of vegetarian diets and risks of depression, Anxiety and Stress, found no significant associations with depression or anxiety, and the only study finding a significant difference in stress found a lower level of stress in those eating strictly plant-based. Other reviews found mixed findings, for example, higher rates of depression, but lower rates of anxiety. Basically, the evidence in the effect of plant-based diets on depression is contradictory. For example, out of 25 studies, 11 found higher rates of depression, 7 found lower rates of depression, and another 7 found no overall correlation. If you drill down, though, and just consider the best quality studies of the four, one found that veg diets had either no risk or a higher risk of depression, depending on the population, and the other three good studies found a lower risk of depression among those eating more plant-based. Drilling down geographically, vegetarianism was not associated with mental health in the United States, Russia, or Germany, but was associated with anxiety and depression in China, though the association was small, explaining less than 1% of the variance in depression and anxiety between individuals. If you drill down by type of vegetarian, only the so-called semi-vegetarians, or flexitarians, had higher rates of depression, whereas than actual vegetarians and vegans. Study results suggested that semi- and pesco-vegetarians, who include fish and or poultry, had a higher risk of depression, whereas no significant association was found for lacto-ovo-vegetarians who eat no meat, and there were similar findings with studies using relative mood scoring, though technically none of the groups achieved statistical significance.

The bottom line is that some systematic reviews have shown no association between vegan and vegetarian diets and mental health outcomes, whereas others have shown associations between vegetarian diets and more depression, while others associate vegetarian diets with less depression. And even if it did go one way or the other, the majority of these studies were just snapshot in time cross-sectional studies, so they are unable to determine cause and effect. Even if following a vegetarian diet was consistently associated with higher or lower rates of depression, there is the possibility of reverse causation. Maybe being depressed leads people to eat vegetarian, rather than eating vegetarian leads to depression. What we need are studies over time to see which came first, and interventional studies to put it to the test, both of which I'll explore next.