Diets heavy in ultra-processed food linked to silent brain damage, study finds

Middle-aged adults who eat the most ultra-processed food are considerably more likely to carry hidden signs of brain injury than those who eat the least, according to a study published in JAMA Network Open this week. The injuries showed up on brain scans even though the participants had no diagnosed heart or vascular disease and no obvious symptoms.

Researchers at McMaster University and Hamilton Health Sciences, led by nutrition scientist Russell J. de Souza and cardiologist Dr. Sonia Anand, examined detailed dietary questionnaires and MRI scans from 8,783 Canadians ages 35 to 69, drawn from two long-running cohort studies. None had cardiovascular disease at enrollment. The team ranked participants by how much of their daily food came from ultra-processed sources — packaged snacks, sugary drinks, reconstituted meats and similar items built largely from refined ingredients and additives rather than whole foods.

Adults in the top quarter of ultra-processed intake, whose diets were made up of nearly half such foods, had 40 percent higher adjusted odds of vascular brain injury than those in the bottom quarter, whose diets were about one-sixth ultra-processed food. The injuries in question were covert brain infarcts and heavy loads of white matter hyperintensities, both markers doctors associate with so-called silent strokes: tiny areas of damage that produce no noticeable symptoms but are considered early warning signs for future strokes and memory problems. The result held after adjustment for age, sex and other factors, and the trend across intake levels was statistically significant.

Diet, body fat and the brain

The heaviest consumers of ultra-processed food also carried more body fat and more visceral fat — the deep abdominal fat that wraps around internal organs and is linked to inflammation and blood vessel damage. Body fat percentage was 1.7 percentage points higher and visceral fat volume was greater by about 5.7 milliliters in the highest-intake group compared with the lowest. There was no significant difference in liver fat, and ultra-processed intake was not linked to scores on two standard cognitive tests, the Montreal Cognitive Assessment and the Digit Symbol Substitution Test.

"I would not have expected this finding, frankly," de Souza said in a statement describing the findings, adding that he had not expected to see the association in healthy, middle-aged adults. Anand, the study's senior author, said the results suggest the link between diet and brain health may be detectable before people experience noticeable problems with memory or thinking, and that eating patterns in a person's 30s through 60s may shape brain health decades later.

The authors also found that heavier ultra-processed eaters ate proportionally less whole food — fruit, vegetables, grains and minimally processed staples made up about 41 percent of servings in the highest-intake group, against 68 percent in the lowest — suggesting packaged and reconstituted products were displacing, rather than simply supplementing, a more traditional diet.

The study is cross-sectional, meaning diet and brain scans were captured at a single point in time, so it cannot establish that ultra-processed food caused the brain changes. The researchers said longitudinal work, with repeat scans over years, is needed to confirm the direction of the relationship and to see whether cutting back on packaged and reconstituted foods can slow or prevent the damage; such follow-up research is already underway, according to a summary of the findings distributed to health reporters.

Covert brain infarcts and white matter damage are the kind of findings that the National Heart, Lung, and Blood Institute associates with elevated risk for a future clinical stroke, even when a person has never had one. Stroke remains a leading cause of death and long-term disability in the United States, and the Centers for Disease Control and Prevention lists lifestyle habits, including diet, among the factors that can be modified to lower that risk. Ultra-processed foods account for more than half of calories in the typical American diet, by most published estimates, well above the roughly one-quarter average recorded among the Canadian participants.

The authors stopped short of specific dietary advice, saying only that further research should clarify whether cutting ultra-processed food earlier in adulthood protects the brain later in life.