We know the drill. Ultra-processed foods (UPFs) are generally bad news. They’re loaded with sugar, salt, saturated fats, and additives that push up the risk of heart disease, type 2 diabetes, and certain cancers. But for years, the damage to our bodies overshadowed the impact on our minds. That’s changing now.
Lately, the data has grown too loud to ignore. There’s a mounting body of evidence linking high UPF consumption to depression, anxiety, and even dementia. I dug into the studies to see if this is just another health scare or if there’s a real, tangible reason to purge the processed stuff from your pantry.
The Causality Problem
Let’s get the nitpicky part out of the way first. Nutrition studies are messy. Most of the research we have is observational. We see that people who eat lots of processed foods tend to have poorer brain health, but correlation isn’t causation. Maybe people with early cognitive issues turn to junk food. Maybe they lack the money to buy fresh produce.
Then there’s the definition problem. Most researchers use the NOVA classification system to categorize food processing levels. But the system has limits. As Tim Spector, co-founder of nutrition science company Zoe, points out, it groups heavily processed items with minimally processed ones just because of structural changes. Weetabix ends up in the same bin as high-sugar energy drinks. That doesn’t tell us much about nutritional impact.
So, what does the data actually show when you strip away the noise?
The Cognitive Cost of UPFs
The signals are becoming impossible to dismiss. A 2024 study tracked nearly 30,000 adults for up to 18 years. The finding was stark: for every 10 percent increase in the share of ultra-processed foods in a person’s diet, their risk of cognitive impairment and stroke went up significantly. This held true even when researchers accounted for income, alcohol intake, and physical activity levels.
Another study looked at 10,775 Brazilian adults over eight years. Those getting more than 19.9 percent of their calories from UPFs suffered faster declines in global cognition and executive function. That’s the mental ability to control impulses and stay focused. Crucially, the decline was noticeable in people under 60. Middle age matters more than we thought.
It’s not just “brain fog.” In 2025, analysts reviewing data from 58,000 people aged 40 to 70 found a direct association between high UPF intake and higher risks of dementia, Parkinson’s, and multiple sclerosis.
Depression and the Gut-Brain Axis
The link isn’t limited to neurodegeneration. Mental health is taking a hit, too. One large study followed over 31,000 female nurses for 14 years. Those consuming more than 8.8 daily servings of UPFs—including things like ready meals, processed meats, and artificially sweetened drinks—were 49 percent more likely to develop depression.
Researchers tried to rule out reverse causality—the idea that depressed people just eat worse. They used advanced statistics to control for this, but it’s hard to fully separate diet from mental state. Still, the alternative view is encouraging. The Mediterranean diet, which is low in UPFs, is linked to lower rates of depression and anxiety. Switching to this pattern can actually ease existing symptoms.
So why is this happening? What are these foods doing to your skull?
“High-fat and high-sugar diets induce low-grade inflammation. We now know that there’s a close link between that inflammation and mental health.”
Likely it’s the gut. UPFs disrupt the microbiome, reducing bacterial diversity. This damages the gut lining, creating “leaky” walls that allow harmful substances into the bloodstream and, eventually, the brain. That triggers low-grade inflammation. Inflammation is now known to be a key driver of depression.
Rapid Changes in Brain Signaling
It’s not just long-term wear and tear. The effects can be immediate. A small but revealing study published recently by Laura Bojarskaite’s team at the University of Oslo showed that men who ate an extra 1,500 calories a day from ultra-processed snacks for just five days altered their brain’s response to insulin.
Insulin helps cells absorb glucose for energy. When it stops working right—insulin resistance—it’s linked to depression and Alzheimer’s. The study showed that these brain signal changes persisted even a week after returning to normal diets. It suggests that a lifelong heavy UPF diet could accelerate brain aging through rapid, reversible-looking but persisting metabolic shifts.
There’s also early evidence suggesting high-UPF diets are linked to a reduction in the volume of the hippocampus. That’s the part of the brain responsible for memory. Less volume means poorer memory. It’s another pathway to cognitive decline.
What Should You Eat?
Tim Spector is blunt about the current consensus: “Eating UPFs regularly is likely to increase your risk to poor mental health.” He warns that because NOVA categories are inconsistent, we might be underestimating the harm.
You don’t need to be a perfectionist. Laura Bojarskaite suggests we stop treating UPFs as “go-to” foods. Focus on cutting out the products that stack the odds against you—those combining added sugars, high salt, and low fiber. Replace those first.
If that still feels like too much homework, Ted Dinan from University College Cork offers a simpler rule for better brain health. Eat more fiber. Eat more oily fish. Two changes. Two huge wins.
The science isn’t finished. But the direction is clear. Your brain is talking. You’re just starting to listen.
