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High ultra-processed food consumption is linked to a higher risk of mental health problems in the long term. Image credit: FreshSplash/Getty Images.
  • The more that a person’s daily calories come from ultra-processed foods, the more likely they are to experience depression long-term, a new study suggests.
  • The association between these foods and depression persisted regardless of sex, body mass index, age, marital status, social living situation, or level of physical activity.
  • Australia’s population gets a high percentage of their daily calories from ultra-processed foods, but residents of the United States and the United Kingdom residents get even more.

According to a new study from Australia, whose results appear in the Journal of Affective Disorders, people who consume a diet high in ultra-processed foods are more likely to experience depression as much as a decade later.

Implicating diet as a source of depression, one of the world’s most common mental health conditions, suggests that changing one’s diet is potentially a pathway to better mental health, though further research is necessary.

Australia is a country with one of the highest rates of consumption of ultra-processed foods, with residents getting, on average, over 40% of their daily calories from highly processed sources.

Ultra-processed foods are manufactured foods typically containing five or more ingredients. They are optimized for flavor and an extended shelf life rather than for nutrition. As a result, they often contain sweeteners, preservatives, emulsifiers, artificial colors and artificial flavors.

The researchers who conducted the recent study analyzed data from 23,299 individuals between 27 and 76 years of age who participated in the Melbourne Collaborative Cohort Study.

They disqualified people exhibiting psychological distress at the outset of the study and 30 days before based on psychological distress questionnaires.

Participants were followed up for 13 to 17 years, at which time their emotional health was measured using the ten-item Kessler Psychological Distress Scale.

To gain a wider view of ultra-processed food consumption so as to be able to assess its effects at various levels, the researchers included and oversampled immigrants from Southern Europe. This is an area in which ultra-processed foods play a smaller role in daily diets.

The researchers found that adolescents who consumed ultra-processed foods regularly were more likely to have depression symptoms a decade later than their counterparts who followed healthier diets.

The association between ultra-processed foods and subsequent depression was unaffected by sex, age, or body mass index. It also persisted regardless of marital status, the number of people a person lived with, and their level of physical activity.

“While Australians eat a lot of ultra-processed foods, the link with depression had never been assessed in a group of Australians,” said first author Dr. Melissa Lane. “The findings, a first for an Australian population-based sample, associated high consumption of ultra-processed foods with an elevated risk of depression.”

The association between ultra-processed foods and mental health appears to be linear.

”We noticed that when people ate more or increasing amounts of ultra-processed foods, their chances of getting depressed went up,” said Dr. Lane.

“This risk became higher than what most people in our study experienced when ultra-processed foods made up about 30% of everything they ate.”

An observational study such as this one cannot firmly establish causation. A question that remains is: Do ultra-processed foods lead to depression, or does depression lead people to eat more ultra-processed foods?

The study may offer clues, but no hard answers.

André de Oliveira Werneck, a doctoral researcher in the Department of Nutrition at the University of São Paulo, Brazil, who was not involved in the study, noted that “[t]he authors excluded participants from the cohort who were undergoing depression treatment during the baseline, which reduces the possibility of reverse causality.”

“However,” he added, “it should be noted that the Kessler Scale was not administered during the baseline [and was given only at follow-up], which is a limitation for establishing causality.”

Still, Werneck cited other research that suggests ultra-processed foods may be the cause of this relationship.

A link between ultra-processed food and psychological distress has not yet been determined. However, said Dr. Lane:

“[Ultra-processed foods] tend to lack important nutrients like protein and fiber, while containing excessive amounts of carbohydrates, saturated fat, and energy. These factors have been associated with gut problems and inflammation, which are linked to depression.”

Although investigations have focused primarily on animals and must be done with humans, said Dr. Lane, “[c]ertain additives and compounds formed during intense food processing or found in packaging may also influence mental well-being through their influence on the gut and the immune system.”

Deriving a significant portion of one’s calories from ultra-processed foods is more common in some parts of the world than others.

“There is evidence,” added Werneck, “that sales of ultra-processed products are higher in North American and Australasian countries, as well as in Western European countries.”

He noted that “most studies in the United States and the United Kingdom have found a contribution of ultra-processed foods to the total energy intake above 50%, while in countries such as Brazil, the consumption is less than 25%.”

While no one can go back and change their previous eating habits, it may be that discontinuing ultra-processed food consumption now may be able to benefit mental health going forward.

“There is a clinical trial — conducted by Dr. Lane and colleagues — which examined the effect of dietary changes on depressive symptoms in individuals with depression (SMILES Trial),” Werneck reported.

“The results, recently published in a preprint and currently under peer review, are extremely promising,” said Werneck. “The nutritional intervention reduced depressive symptoms by reducing the consumption of ultra-processed foods.”