Scientists Link Ultraprocessed Foods to Depression

Tucking into a bag of potato chips might be all you want to do on a bad day but scientists have discovered that foods like this might increase your risk of depression.

Eating ultraprocessed foods (UPF)—defined as energy-dense, palatable, and ready-to-eat items—in particular artificial sweeteners and artificially sweetened beverages, has been found to be associated with increased depression risk, according to a new paper in the journal JAMA Network Open.

The paper found that women who ate the highest level of ultraprocessed food had a 50 percent higher risk of developing depression in the future compared with those women that ate the lowest amount.

"There have been several studies which have supported an important role for diet in influencing the risk of depression," Andrew T. Chan, a professor of medicine at Harvard Medical School, doctor at Massachusetts General Hospital, and study co-author, told Newsweek. "However, there have been scant data about what specific elements of diet may mediate that association. We conducted a comprehensive study which assessed whether ultraprocessed foods may influence risk of developing depression several years later."

The study looked at the diets of 31,712 women, aged 42 to 62 years, and compared the elements of their diets to their mental health, using both self-diagnosed and clinically diagnosed depression.

They found that some foods, including artificial sweeteners and artificially sweetened beverages, were particularly bad regarding depression risk.

"Animal studies have suggested a link between artificial sweeteners and depression. Our study is among the first to indicate that this may be relevant to humans," Chan said. "Artificial sweeteners may trigger the transmission of particular signaling molecules in the brain that are important for mood."

This link between sweeteners and depression may be a result of the transmission of purine in the body, which has been seen in other studies on animals. Purine is a natural substance found in some foods and known to cause gout.

"There are many possible ways artificial sweeteners might be associated with depression," Richard Hoffman, an associate lecturer in nutritional biochemistry at the University of Hertfordshire in the U.K., told Newsweek.

"There is not much specific information on the purinergic pathway," he said. "But people with UPF-rich diets are often nutrient deficient. So one simple explanation is that the people consuming diets high in UPFs were deficient in certain nutrients, and that this increased their risk of depression. For example, deficiencies in vitamin B12, folate and omega-3 fatty acids (EPA/DHA) are all associated with an increased risk of depression."

"Inflammatory effects are another possibility. Healthy diets low in UPFs are more anti-inflammatory and this has been linked to a lower risk of depression," he said.

These findings complement previous studies which have found that foods that are minimally processed actually lower depression risk.

"We do know that being able to eat a Mediterranean-style diet with plenty of vegetables, fruit, nuts, seeds and pulses is associated with a lower risk of living with depression," Duane Mellor, the lead for evidence-based medicine and nutrition at Aston University in the U.K.'s Aston Medical School, told Newsweek.

One woman—Aimee Kingston—and her twin sister Nancy previously took part in a King's College London study where they both ate the same number of calories, but one ate UPFs and the other only unprocessed foods. They found that the one eating the UPF diet was much more hungry and tired in comparison with her sister, and had gained weight after only two weeks.

Some experts have suggested that a correlation between UPFs and depression may be caused by patients feeling depressed and as a result consuming these foods, including drinks containing artificial sweeteners, rather than healthier alternatives.

"Although it is possible that these drinks could have these effects, it is perhaps more likely that reverse causality may be happening, in that people living with depression might be seeking different foods and drinks, and then consuming sweetened drinks," Mellor said. "So we do not know if these foods increase risk of developing low mood and poor mental health or if poor mental health impacts food choice."

"We assessed people's diet years before they developed depression, we think it is less likely that our results are due to depression causing people to eat ultraprocessed food," Chan said.

People may eat these kinds of foods because it makes them feel happier in the short-term, however.

"In my own work, I have in fact recently speculated that UPFs are often consumed in an attempt to feel happier and that some UPFs are the equivalent of soma—the happiness drug invented by Aldous Huxley in Brave New World," Hoffman said.

There were some limitations to the latest study, the authors note, because of the demographics of the patients involved.

"The cohort primarily included non-Hispanic White females," they wrote in the paper. "Additionally, without structured clinical interviews, misclassification of the outcome may be considered."

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