RESOLVING THE LEDGER
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Microwave meals and other ultra-processed foods can affect your brain health
By now, we all know that ultra-processed foods (UPFs) aren’t particularly good for our bodies. UPFs, which are often high in sugar, salt, saturated fat and additives, have been repeatedly linked with an increased risk of heart disease, diabetes and some cancers. But until recently, far less attention has been paid to what these foods might be doing to our brains. Could the typical Western diet, packed with highly processed foods, be affecting how we think and feel too?
Lately, I’ve noticed an increasing number of studies linking UPFs with depression, anxiety and even dementia. I wanted to look at how strong the evidence is, and whether it offered another persuasive reason to eliminate them from my diet.
The immediate problem, as with many nutrition studies, is that, while many observational studies have found associations between greater intake of UPFs and various brain health problems, direct causal evidence is less forthcoming.
The picture is further complicated by how we define UPFs, says Tim Spector at Kings College London, the co-founder of nutrition company Zoe. Most countries use the NOVA classification system, which is designed to categorise levels of processing, but not to assess how a food impacts health. “The fact that Weetabix, with very few ingredients and hardly any sugar, salt or fat, is in the same class as high-sugar energy drinks tells you all you need to know about its limitations,” says Spector.
That said, evidence is mounting for the harms of UPFs. In 2024, a study involving around 30,000 people who first underwent testing between 2003 and 2007 and were followed for up to 18 years, showed that for every 10 per cent increase in the proportion of UPFs in a person’s diet, the risk of cognitive impairment and stroke rose significantly. This association remained even when considering confounding factors such as income, alcohol consumption and physical activity.
Another study followed 10,775 adults in Brazil for around eight years. Those who obtained more than 19.9 per cent of their energy from UPFs experienced faster declines in global cognition – an overall assessment of mental ability – and executive function, which is the ability to control impulses, regulate emotions and stay focused. Interestingly, this team also found that UPFs were linked with increased cognitive decline in people under 60 years of age. This, they argued, emphasises the importance of eating more whole foods in middle age.
It’s not just general cognitive decline, either. In 2025, researchers analysing data from 58,423 people between the ages of 40 and 70 found that increased UPF consumption was associated with a higher risk of dementia, Parkinson’s disease and multiple sclerosis.
Other studies have shown links between UPFs and depression and anxiety, too. In one, researchers followed 31,712 female nurses between 2003 and 2017, who were free from depression at the start of the study. Those eating more than 8.8 servings a day of UPFs – which may have included things like artificially sweetened drinks, sauces, processed meat or a ready-made meal – had a 49 per cent higher risk of developing depression. Although observational, the study used some advanced statistical analyses to broadly rule out “reverse causality” – the argument that if you’re depressed, you may be more tempted to eat less-healthy foods.
We can also look at the problem from the opposite direction, too. The Mediterranean diet tends to be low in UPFs and has been linked with a lower risk of depression and anxiety, for instance, and there’s increasing evidence that switching to this diet can ease existing symptoms of depression.
Again, all these studies find correlations, not causation, but that’s a lot of correlation. So what might UPFs be doing that is so bad for the brain? The answer is likely to involve multiple, overlapping pathways. For instance, many UPFs are high in salt, fat and sugar, all of which are known to disrupt the gut microbiome, shifting it so that it has less diversity and fewer beneficial bacteria. This can damage the gut lining, making it “leakier” and allowing harmful substances into the blood and brain. “High-fat and high-sugar diets also induce low-grade inflammation,” says Spector. “We now know that there’s a close link between inflammation and mental health, particularly depression.”
Laura Bojarskaite at the University of Oslo in Norway points me to a small study published last year that found that just five days of eating an extra 1500 calories from ultra-processed snacks altered men’s brain responses to insulin, a hormone that helps cells take up glucose for energy. The effect remained detectable a week after they returned to their normal diets.
Insulin regulation is vital for maintaining cognitive function, while insulin resistance is linked with depression and Alzheimer’s. Although the study didn’t look at brain health specifically, it provides evidence that UPFs can rapidly modify brain signalling, which Bojarskaite says is a “credible pathway through which a lifelong [UPF-heavy] diet could influence brain ageing".
I also found early evidence that diets high in UPFs are associated with a reduction in volume of the hippocampus in adults, perhaps because the foods have fewer nutrients vital for growth. This region is heavily involved in memory, so this may be yet another reason why UPFs are linked to cognitive decline.
“In my opinion, the evidence is pretty clear: eating UPFs regularly is likely to increase your risk of poor mental health,” says Spector. He adds that current studies may even have underestimated their effect because of the inconsistencies in NOVA scores.
Bojarskaite says our goal should be to stop UPFs from becoming our “go-to” foods. Rather than trying to eliminate every UPF from our diet, she says we should concentrate on reducing products that combine multiple unfavourable features – like added su...
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