Does a Healthy Diet Lower Risk of Depression?

We know that what we eat has a big impact on our risk for heart disease, type 2 diabetes, cancer, and other common conditions, but the relationship between diet and mental illnesses, including depression, is less clear and significantly less studied.

Many observational studies (those that track a large group of people over time with altering their behavior) have shown that individuals who eat a generally healthy diet have a lower risk of developing depression. Adding to this body of research, a study published this week found that Spanish adults who followed a diet pattern high in vegetables and other whole foods and low in sugar, salt, and red meat were less likely to report a depression diagnosis compared to people who ate less nutritious foods. The study, published in the journal BMC Medicine, also found that adhering to a Mediterranean-style eating pattern high in fish, beans and healthy fats or a plant-based diet with limited meat, eggs, and dairy was associated with a reduced risk of depression.

While these results are certainly meaningful and important, there are many limitations to consider. First and foremost, this was an observational study, not a randomized controlled trial, which means it can’t prove that participants’ eating habits caused changes that prevented depression. The people who followed more nutritious diets may have also been healthier in other ways that also impacted their risk of mental illness. Although the researchers controlled for individuals’ exercise habits, supplement use, weight status, and history of chronic diseases by building these factors into their statistical model, this method isn’t perfect and may not completely cancel out the impact that other lifestyle habits have on mental health. In addition, the researchers relied on participants to self-report their depression, rather than confirming the medical diagnosis.

Research on Diet and Depression Is Limited

Randomized controlled trials deliver the highest-quality scientific evidence, but unfortunately few have been conducted to examine the relationship between overall diet or specific nutrients and depression. In one recent large trial, researchers assigned participants to follow either a low-fat control diet, a Mediterranean-style diet supplemented with olive oil, or a Mediterranean-style diet supplemented with nuts, and found that neither of the Mediterranean diets reduced depression rates among participants. Another study, nicknamed the SMILES trial, is currently underway to determine whether a healthy eating program can improve symptoms in people already living with major depression. Half of the participants will be attending a series of nutrition counseling sessions over a six-month period while the other half will not receive any diet advice. We’ll have to stay tuned to see the results. Trials like this can help to clarify whether a poor diet is a cause or symptom of depression and other mood disorders. Living with depression may decrease individuals’ ability and desire to prepare and eat nutritious, balanced meals, so it’s important to determine where diet fits into the progression of the disease.

The new Spanish study and others like it examine the impact of overall diet quality on depression risk, rather than individual foods. However, many health experts claim that specific foods and nutrients can help to alleviate depression or improve mood. Most of these claims are based on observational research, rather than trials that give people a specific food or nutrient to test whether it actually reduces the incidence of depression or resolves symptoms.