The link between highly processed foods and brain health

About 60 percent of the calories in the average American diet come from highly processed foods. We’ve known for decades that eating packaged items like some breakfast cereals, snack bars, frozen meals, and virtually all packaged desserts, among many other things, is linked to undesirable health effects, such as an increased risk of diabetes, obesity, and even cancer. But more recent studies point to another big downside to these often delicious and always convenient foods: They seem to have a significant impact on our minds, too.

Research over the past decade has shown that the more highly processed foods a person eats, the more likely they are to feel depressed and anxious. Some studies have suggested a link between UPF consumption and increased risk of cognitive decline.

What is so insidious about these foods and how can you avoid mental relapse? Scientists are still working on answers, but here’s what we know so far.

What qualifies as an ultraprocessed food?

In 2009, Brazilian researchers put food on a four-part scale, from unprocessed and minimally processed (such as fruits, vegetables, rice, and flour) to processed (oils, butter, sugar, dairy, some canned foods, and meat and smoked fish) and ultra-processed. Ultraprocessed 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, said Eurdice Martnez Steele, researcher in food processing 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 you find in the frozen food aisles of grocery stores and on the menu of fast-food restaurants. 70 percent of packaged foods sold in the United States are considered ultraprocessed. They are increasingly eliminating healthier foods from people’s diets and are widely consumed across all socioeconomic groups.

Ultraprocessed foods are carefully formulated to be so palatable and satisfying that they’re almost addictive, said Dr. Eric M. Hecht, an epidemiologist at Florida Atlantic University’s Schmidt College of Medicine. The problem is that to make products ever tastier, producers make them less and less similar to real food.

What effect do ultra-processed foods have on mental health?

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. There was a significant increase in mentally unhealthy days for those who ate 60 percent or more of their calories from UPF, said Dr. Hecht, the study author. This is not proof of causality, but we can tell 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 consuming ultra-processed foods and worse cognitive function (the ability to learn, remember, reason, and solve problems). While we have a natural decline in these abilities with age, we’ve seen this decline accelerated by 28 percent in people who consume more than 20 percent of their calories from UPF, said Natalia Gomes Goncalves, postdoctoral researcher at the University of Sao Paulo Medical School and lead author of the study.

It’s possible that eating a healthy diet could offset the harmful effects of consuming ultra-processed foods. Brazilian researchers have found that following a healthy diet, such as the MIND diet, rich in whole grains, green leafy vegetables, legumes, nuts, berries, fish, chicken and olive oil, significantly reduces the risk of dementia associated with the consumption of ultra-processed foods. Those who followed the MIND diet but still ate UPF had no association between UPF consumption and cognitive decline, said Dr. Goncalves, adding that researchers don’t yet know what a safe amount of UPF is.

Why might ultraprocessed foods have this effect?

It is not clear. Many high-quality randomized trials have demonstrated the beneficial effect of a nutrient-dense diet on depression, but we still don’t fully understand the role of food processing on mental health, said Melissa Lane, a researcher at the Food & Mood Center in Deakin University in Australia. However, there are some clues.

Much of the research has focused on how poor gut health can affect the brain. Diets high in ultraprocessed foods are typically low in fiber, which is found primarily in plant-based foods such as whole grains, fruits, vegetables, nuts and seeds. Fiber helps feed the good bacteria in your gut. Fiber is also needed for the production of short-chain fatty acids, substances produced when it breaks down in the digestive system and which play an important role in brain function, said Wolfgang Marx, president of the International Society for Nutritional Psychiatry Research and a researcher senior 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.

The chemical additives in UPF might also have an impact on 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 affect the gut microbiome. said Marx.

Poor gut microbiota diversity and a high-sugar diet may contribute to chronic inflammation, which has been linked to a range of mental and physical problems, said Dr. Lane. 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 runs both ways. Diet affects mood, but the reverse is also true, said Dr. Frank Hu, a professor of nutrition and epidemiology at the Harvard TH Chan School of Public Health. When you’re stressed, anxious, or depressed, you tend to eat more unhealthy foods, especially ultra-processed foods high in sugar, fat, and chemical additives.

How to recognize ultra-processed foods

The best way to identify ultra-processed foods is to read product labels. A long list of ingredients, and especially one that includes ingredients you would never use in home cooking, are clues that the food is ultra-processed, said Whitney Linsenmeyer, assistant professor of nutrition at Saint Louis University in Missouri and a spokeswoman for the Academy. of nutrition and dietetics. . Chemical names, unpronounceable words, and anything you’re unlikely to find in a kitchen cabinet are often signs that a food falls into the ultra-processed category.

However, it is possible to use ready-to-eat foods to facilitate cooking without resorting to ultra-processed foods. Products such as canned beans, frozen vegetables, pre-cooked brown rice or canned fish are all quick-choice ingredients that fit well within the scope of a healthy diet, provided there are no industrial products in the ingredients list. If the added ingredients are ones you would use yourself, such as herbs, spices, salt or cooking oils, Dr. Linsenmeyer said, that’s an indication that the food, while processed, isn’t inherently bad for you.