Approximately 60 percent of the calories in the average American diet come from highly processed foods.
We've known for decades that eating these types of packaged goods—like some cereals, bars, frozen meals, and more—is linked to
bad
health consequences, such as increased risk of diabetes, obesity, or even cancer.
A healthy diet improves cognitive aspects.
Photo Shutterstock.
But more recent studies point to another downside to these usually delicious and highly convenient foods: They also seem to have a
considerable impact on our brains.
Research over the past ten years or so has shown that the more ultra-processed foods (UPFs) a person eats, the more likely they are to feel depressed and
anxious
.
Some studies have suggested a relationship between the consumption of UPF and an increased risk of cognitive decline.
What is harmful about these foods and how can you avoid their mental consequences?
Scientists are still searching for answers, but here's what we know so far.
What is considered an ultra-processed food?
In 2009, Brazilian researchers classified foods on a four-part scale, from unprocessed and minimally processed (such as fruits, vegetables, rice, and flour) to processed (oils, butter, sugar, dairy products, some canned foods, as well as such as smoked meats and fish) and ultra-processed.
“
Ultra-processed foods
include ingredients that are rarely used in homemade recipes, such as high fructose corn syrup, hydrogenated oils, protein isolates, and chemical additives” such as colors, artificial flavors, sweeteners, emulsifiers, and preservatives, explained Eurídice Martínez. Steele, a food processing researcher at the University of São Paulo, Brazil.
This classification system is now widely used by nutrition researchers.
UPFs make up the majority of packaged foods found in supermarket freezer aisles and on fast-food restaurant menus:
70 percent of packaged foods sold in the United States are considered ultra-processed.
Its consumption is widespread among the different socioeconomic groups and each time
they displace
the healthiest foods in the diet.
"Ultra-processed foods are painstakingly formulated to be so appetizing and satisfying that it's almost addictive," said Eric M. Hecht, a public health researcher at Florida Atlantic University Schmidt College of Medicine.
"The problem is that, in order for products to taste better and better, manufacturers make them less and less like real food."
What effects do ultra-processed foods have on mental health?
Some recent research has shown a link between highly processed foods and low mood.
In a 2022 study of more than 10,000 adults in the United States, the more UPF participants ate, the more likely they were to report mild depression or feelings of anxiety.
It was causal, but we can say that there seems to be an association.”
"There was a significant increase in bad mood days for those who consumed 60 percent or more of their calories from UPF," said Hecht, the study's author.
"This is not proof of cause and effect, but we can say that there appears to be an association."
New research has also found a connection between high UPF consumption and
cognitive decline.
A
2022 study that followed nearly 11,000 Brazilian adults for a decade found a correlation between eating ultra-processed foods and poorer cognitive function (the ability to learn, remember, reason, and solve problems).
"While we have a natural decline in these capacities with age, we saw this decline
accelerate to 28 percent
in people who consume more than 20 percent of their calories from ultra-processed foods," said Natalia Gomes Goncalves, a professor of the Faculty of Medicine of the University of São Paulo and lead author of the study.
Eating a healthy diet may counteract the harmful effects of eating ultra-processed foods.
Brazilian researchers found that following a healthy diet, such as the
MIND
diet—rich in whole grains, leafy green vegetables, legumes, nuts, berries, fish, chicken, and olive oil—greatly reduced the risk of dementia associated with the consumption of ultra-processed foods.
Those who were on the MIND diet but continued to consume UPF "did not have any association between UPF consumption and cognitive decline," Goncalves said, adding that researchers do not yet know the safe amount of ultra-processed foods in a diet.
Why would ultra-processed foods cause this?
It is not clear.
"Many high-quality randomized studies have shown the beneficial effect of a nutrient-dense diet on depression, but we still don't fully understand the role of food processing in mental health," said Melissa Lane, a Food & Mood researcher. Deakin University Center in Australia.
However, there are some clues.
Much of the research has focused on how
poor gut health
can affect the brain.
Diets rich in ultra-processed foods are often low in fiber, which is found mostly in plant foods such as whole grains, fruits, vegetables, nuts, and seeds.
Fiber helps feed the good bacteria in the gut.
Fiber is also necessary for the production of short-chain fatty acids, substances that are produced when broken down in the digestive system and play an important role in brain function, said Wolfgang Marx, president of the International Society for Psychiatric Research. nutritionist and principal investigator at Deakin University.
"We know that people with depression and other mental disorders have a less diverse composition of gut bacteria and fewer short-chain fatty acids."
UPF chemical additives could also influence the intestinal flora.
“Emerging evidence—primarily from animal studies, but also some human data—suggests that isolated nutrients (such as fructose), additives such as artificial sweeteners (such as aspartame and saccharin), or emulsifiers (such as carboxymethylcellulose) and polysorbate-80) can negatively influence the gut microbiome,” Marx said.
The low diversity of the gut microbiota, as well as a diet high in sugar, can contribute to
chronic inflammation
, which has been linked to a number of mental and physical problems, according to Lane.
“Interactions between increased inflammation and the brain are thought to drive the development of depression,” he said.
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