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. Advertisement 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. Noted.

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.