Why might ultraprocessed foods have this effect?
It’s unclear. “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, there are some clues.
Much of the research has focused on how poor gut health might affect the brain. Diets that are high in ultraprocessed foods are typically low in fiber, which is mostly found in plant-based foods like 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, the substances produced when it breaks down in the digestive system, and which play an important role in brain function, said Wolfgang Marx, the president of the International Society for Nutritional Psychiatry Research and a senior research fellow 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.”
Chemical additives in UPFs might also have an impact on 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,” Dr. Marx said.
Poor gut microbiota diversity — as well as a diet high in sugar — may contribute to chronic inflammation, which has been linked to a host of mental and physical issues, Dr. Lane said. “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. “Diet does influence mood, but the reverse is also true,” said Dr. 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.”
How to recognize ultraprocessed foods
The best way to identify ultraprocessed 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 ultraprocessed, said Whitney Linsenmeyer, an 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 would be unlikely to find in a kitchen cabinet are often signs that a food is in the ultraprocessed category.
You can still use convenience foods to make cooking easier without resorting to ultraprocessed foods. Products such as canned beans, frozen vegetables, precooked brown rice or canned fish are all shortcut ingredients that fit well within the scope of a healthy diet, provided there aren’t any industrial items on the ingredient list. “If the added ingredients are ones you would use yourself, like herbs, spices, salt or cooking oils,” Dr. Linsenmeyer said, “that’s an indication that the food, while processed, is not inherently bad for you.”
