While the consumption of ultra-processed foods (UPFs) has been linked to negative physical health outcomes such as a heightened risk of diabetes, obesity, and cancer, recent research suggests they may also have a significant impact on the health of your brain, Sally Wadyka writes for the New York Times.

The link between UPFs and brain health

According to Eurídice Martínez Steele, a food processing researcher at University of São Paulo, "[u]ltraprocessed foods include ingredients that are rarely used in homemade recipes — such as high-fructose corn syrup, hydrogenated oils, protein isolates and chemical additives."

Currently, 70% of the packaged foods in the United States fall into the ultra-processed category. UPFs are increasingly replacing healthier foods in people's diets, making up around 60% of the calories in the average American's diet.

In recent studies, researchers have demonstrated a link between UPFs and low mood. For instance, a 2022  study  of more than 10,000 U.S. adults found that participants who consumed high levels of UPFs were more likely to report mild depression or feelings of anxiety.

"There was a significant increase in mentally unhealthy days for those eating 60 percent or more of their calories from UPFs," said study author Eric Hecht, an epidemiologist at the  Schmidt College of Medicine  at  Florida Atlantic University. "This is not proof of causation, but we can say that there seems to be an association."

In addition, researchers have identified a connection between high UPF consumption and cognitive decline. A  study  released last year that followed almost 11,000 Brazilian adults over a decade found a correlation between UPF consumption and lower cognitive function, including the ability to learn, remember, reason, and solve problems.

"While we have a natural decline in these abilities with age, we saw that this decline accelerated by 28 percent in people who consume more than 20 percent of their calories from UPFs," said lead study author Natalia Gomes Goncalves, who is a professor at the University of São Paulo Medical School.

Researchers have said that eating a healthy diet may offset the negative impacts of eating UPFs. For example, individuals who followed the MIND diet while consuming UPFs "had no association between UPF consumption and cognitive decline," Goncalves said, noting that researchers still have yet to determine what level of UPF consumption is safe.

Why do UPFs have a negative impact on brain health?

Currently, researchers still do not understand the link between UPF consumption and cognitive health.

"Many high-quality, randomized  studies have shown the beneficial effect of a nutrient-dense diet on depression, but we still do not fully understand the role of food processing on mental health," said Melissa Lane, a researcher at the  Food & Mood Centre at Deakin University in Australia.

However, research does provide some clues. A lot of the research surrounding this link is focused on the impact poor gut health might have on the brain.

"Diets that are high in [UPFs] are typically low in fiber, which is mostly found in plant-based foods like whole grains, fruits, vegetables, nuts and seeds," Wadyka writes. "Fiber helps feed the good bacteria in the gut."

According to Wolfgang Marx, the president of the International Society for Nutritional Psychiatry Research and a senior research fellow at Deakin University, fiber is also necessary to produce short-chain fatty acids, which play a key role in brain function.

"We know that people with depression and other mental disorders have a less diverse composition of gut bacteria and fewer short-chain fatty acids," Marx said.

In addition, research suggests that the chemical additives in UPFs could also impact gut flora. "Emerging evidence — mostly from animal studies, but also some human data — suggests that isolated nutrients (like fructose), additives such as artificial sweeteners (like aspartame and saccharin) or emulsifiers (like carboxymethylcellulose and polysorbate-80) can negatively influence the gut microbiome," Marx said.

Lane also noted that things like poor gut microbiota diversity and a high-sugar diet may contribute to chronic inflammation, which is associated with a variety of mental and physical issues. "Interactions between increased inflammation and the brain are thought to drive the development of depression," she said.

"It's also worth considering the possibility that the link between highly processed foods and mental health works in both directions," Wadyka writes.

"Diet does influence mood, but the reverse is also true," said Frank Hu, a professor of nutrition and epidemiology at the Harvard T.H. Chan School of Public Health. "When you get stressed, anxious or depressed, you tend to eat more unhealthy foods, in particular ultraprocessed foods that are high in sugar, fat and chemical additives." (Wadyka, New York Times, 5/4)