Eating less ultraprocessed food could have an effect on depression symptoms, according to a small new study, but researchers caution that it's much too early to consider the dietary change a treatment for depression.
The study, which was published in JAMA Psychiatry, included just 20 adults with depression who also had a high body weight and at least one metabolic condition, such as high blood pressure, diabetes or unhealthy cholesterol levels. Its main purpose was to find out whether people could make a major reduction in ultraprocessed foods in their everyday lives. Changes in depression and anxiety were also tracked, but those were not the study's primary focus.
Participants spent four weeks eating their usual diet and four weeks eating a diet with very little ultraprocessed food. Half started with one diet and half with the other before switching. They weren't given prepared meals. Instead, they shopped for their own food with guidance from the researchers.
The change in eating habits was substantial. Participants cut their ultraprocessed food consumption by more than 85%, and 19 of the 20 people completed the study.
During the low-ultraprocessed-food period, participants also reported fewer symptoms of depression. The improvement appeared across three different measures used to assess depression. Anxiety symptoms improved more modestly.
Those results are intriguing, but they don't show that eating less ultraprocessed food was responsible for the improvement.
This was a very small study, and participants knew when they were changing their diets. Researchers also relied on participants to report what they ate. The authors themselves describe the changes in depression and anxiety as preliminary findings that need to be tested in larger studies.
There's another important question the study couldn't answer: What about the dietary change might have mattered?
Eating much less ultraprocessed food means eating differently in other ways, too. Participants may have changed how many calories they ate or their intake of sugar, fat and other nutrients. They also may have consumed fewer additives found in some ultraprocessed foods. The study couldn't determine which, if any, of those changes might have contributed to the differences in mood.
That makes it difficult to conclude that food processing itself was responsible.
The researchers also didn't establish a biological explanation for the changes in depression symptoms. Although scientists are investigating several possible connections between diet and mental health, this study wasn't designed to show how eating fewer ultraprocessed foods might affect the brain or mood.
The people who participated were a fairly specific group. Their average age was about 44, 70% were women and everyone had a high body weight and at least one metabolic condition. Fourteen of the 20 also had anxiety. Some participants were taking psychiatric medications or receiving therapy, which they were asked to keep unchanged during the study.
For those reasons, the results can't necessarily be applied to everyone with depression. And the study doesn't show that changing diet can replace medication, therapy or other established depression treatments.
What it does provide is an early reason to keep investigating.
Researchers showed that people with depression could make a substantial reduction in ultraprocessed food for several weeks while choosing and buying their own food. Participants generally considered the dietary change useful, although they found it somewhat challenging to follow. During that same period, their depression scores improved.
A larger trial could help determine whether those improvements persist in more people and whether reducing ultraprocessed foods actually plays a role.
The study was supported by the National Center for Advancing Translational Sciences, National Heart, Lung, and Blood Institute, National Institute of Mental Health and UCSF Weill Institute of Neurosciences. Senior author Andrew Krystal reported research funding, consulting or advisory relationships and stock options involving several pharmaceutical and health companies outside this study.