There are several factors that can cause depression, including genetics, brain chemistry, stress, trauma and life circumstances. Researchers are also increasingly exploring another possible factor, your diet. A new pilot study published in JAMA Psychiatry has found that reducing ultra-processed foods may help improve symptoms of depression. The study, led by researchers at the University of California, San Francisco, looked at whether changing what people eat could affect their mental health.

The study was small, involving only 20 people, and was designed mainly to test whether a larger clinical trial would be practical. The researchers also point out that previous studies have mainly found an association between higher ultra-processed food intake and depression, rather than proving that these foods directly cause depression. The new research is important because it examines what happens when people with depression actually change their diet.

What Did The New Study Find?

The study included adults with major depressive disorder who consumed a large proportion of ultra-processed foods. Participants followed their usual diet for four weeks and a low-ultra-processed-food diet for another four weeks, with the order of the diets varied between participants.

During the low-ultra-processed-food phase, participants reduced their intake of these foods by more than 85%. Researchers found moderate to large improvements across three different measures of depression. Anxiety symptoms also improved, although the change was smaller. The study therefore suggests that reducing ultra-processed food intake could potentially be explored as one part of a broader approach to managing depression. However, because of the small sample size and short duration, larger and longer studies are needed before firm conclusions can be drawn.

Nyasha Chagwedera, MD, PhD, corresponding author, assistant professor, UCSF Department of Psychiatry and Behavioral Sciences, said, "Reducing the amount of ultra-processed food in our diet can be challenging, because it's highly palatable, cheap, and convenient. Ultra-processed food triggers dopamine, the pleasure hormone, which promotes craving. Food companies work with scientists to find just the right amount of sugar, salt, and fat that make you want to eat more and more."

What Are Ultra-Processed Foods?

Ultra-processed foods are industrially manufactured products that often contain several added ingredients and additives. They can include:

  • Packaged snacks and sweets
  • Sugary drinks
  • Fast food
  • Ready-to-eat or ready-to-heat meals
  • Some packaged baked products
  • Processed meat products
  • Foods containing additives such as flavour enhancers, emulsifiers, preservatives or artificial colours

It is important to note that not every packaged food is necessarily ultra-processed. Processing itself is not automatically unhealthy. The concern in this study was specifically about foods classified as ultra-processed.

How Can Diet Be Connected To Depression?

Researchers are studying several possible pathways linking diet and mental health. One possibility involves the gut-brain connection.

The gut contains a large community of microorganisms that interact with the digestive system, immune system and nervous system. Diet can influence this environment. Researchers involved in the study suggest that diets high in ultra-processed foods may affect the gut and contribute to inflammation, which could potentially influence brain function and mood. However, the researchers stress that a direct mechanism between ultra-processed food and major depressive disorder has not yet been established.

Another possibility is that diets dominated by ultra-processed foods may provide fewer nutrients found in a varied diet that have vegetables, fruits, whole grains, legumes, nuts and other minimally processed foods. Poor overall dietary quality may affect several aspects of health that are also connected with mental wellbeing.

Does This Mean Diet Can Replace Depression Treatment?

No, this study does not show that people with depression should stop medication or therapy and change their diet instead. Depression is a serious medical condition, and treatment may involve psychotherapy, medication, lifestyle changes or a combination of these approaches. Any changes to treatment should be discussed with a healthcare professional.

Diet can be considered as one part of overall health, particularly when it involves gradually replacing highly processed foods with more nutritious choices.

Researchers say that they expect to start enrollment in phase 2 of the study in 2028.

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