HAMILTON, Ont. - Healthy adults who eat high amounts of ultra-processed food, like packaged snack foods, sugary breakfast cereals, soft drinks, instant noodles, and ready-to-eat frozen meals, are more likely to have signs of damage to the brain that may increase the chances of clinical stroke and future memory problems.
Researchers used magnetic resonance imaging (MRI) to scan the brains of nearly 9,000 people and detected tiny areas of damage more frequently in participants who ate the most ultra-processed food compared to those who ate the least. Participants with the highest intake were 40 per cent more likely to show these changes, which produce no obvious symptoms but are considered early warning signs that can appear years before a stroke or memory problems begins.
"I would not have expected this finding, frankly. We studied middle-aged Canadians who had no heart problems and reported no other health concerns," said Russell J. de Souza, first author of the study and an associate scientist at the Population Health Research Institute (PHRI) of McMaster University and Hamilton Health Sciences, and associate professor in Health Research Methods, Evidence, and Impact and the Heersink School of Global Health and Social Medicine at McMaster University.
"Usually, this kind of damage is associated with conditions we hear about and treat at a much older age."
Published in JAMA Network Open on Oct. 15, 2026, the PHRI led study enrolled Canadians between the ages of 35 and 69 with no history of heart disease from communities across Canada.
Participants who ate the most ultra-processed food also carried more body fat and more deep belly fat than those who ate the least. This type of abdominal fat is linked to inflammation and blood vessel damage that can also reach the brain.
The association between ultra-processed food and brain damage appeared stronger among women. Those in the highest consumption group were nearly twice as likely to show signs of brain damage compared with those in the lowest group.
"Our findings suggest that the link between diet and brain health may be detectable before people experience noticeable problems with memory or thinking," said Sonia Anand, senior author of the study and senior scientist at PHRI. "This adds to the growing evidence that what Canadians eat in their 30s, 40s, 50s and 60s shapes their brain health later in life."
Researchers classified foods according to the extent and purpose of industrial processing used in their production. Ultra-processed foods are often high in sodium, added sugars, and saturated fats, while providing relatively low amounts of fibre, vitamins, and minerals. Their convenience, widespread availability, and intensive marketing may contribute to higher consumption, particularly among time-constrained and lower-income households, potentially widening existing health inequalities.
"For many Canadians, ultra-processed food is often a convenient and affordable option. But our findings suggest that diets high in these foods may be linked to brain changes that may lead to memory loss and stroke as Canadians grow older," said Anand.
In this study, ultra-processed foods made up an average of about 25 per cent of participants' daily food servings. For the heaviest consumers, that increased to 45 per cent of everything on their plates, compared with just 16 per cent for those who ate the least.
Researchers found that as the consumption of ultra-processed food increased, that of whole food decreased. Fruits, vegetables, grains and other minimally processed foods made up 41 per cent of daily servings among participants with the highest consumption of ultra-processed food, compared with 68 per cent among those with the lowest consumption.
"People who ate more ultra-processed foods weren't simply eating more on top of their usual diet. These foods appeared to crowd out healthier whole foods," added de Souza.
Researchers analyzed data from participants enrolled in two PHRI studies: the Canadian Alliance for Healthy Hearts and Minds and the Prospective Urban and Rural Epidemiology-MIND study. They completed detailed dietary questionnaires and underwent MRI brain scans reviewed by neurologists who were unaware of the participants' dietary patterns.
The findings suggest a link between ultra-processed food consumption and signs of brain changes. However, because participants were only assessed once and weren't followed over time, researchers couldn't determine whether ultra-processed foods directly caused these changes.
"We need longer-term studies that track people over time with repeated MRI scans to find out whether reducing ultra-processed food intake can slow or prevent these brain changes," said de Souza. "Such follow-up is ongoing."
The study was supported by the Canadian Partnership Against Cancer, the Heart and Stroke Foundation of Canada, and the Canadian Institutes of Health Research, with additional support from participating research institutions and partner organizations across Canada.
