A Month in the Scanner

The Four-Week Diet

Mara: Chris van Tulleken, a doctor and associate professor at University College London, made himself the experiment. For four weeks he'd get 80% of his calories from ultra-processed food, eat normally, and keep the rest of his life the same. One of Britain's top obesity experts supervised. According to University College London Hospitals, she scanned his brain with MRI at the start, and again at the end. In between, he put on about six kilos. That was enough to tip his BMI, his body mass index comparing weight to height, into the obese range.

Eli: And that's the listener's question, sitting right there in the scanner: can eating a lot of ultra-processed food really damage the brain? Today's angle is whether eating a lot of ultra-processed food can really damage your brain.

Mara: Between those two scans sat a month of eating, with one doctor's brain as the test case. One brain, though, can't settle what this food does to everyone's.

Eli: The headlines are less patient. One read: 'Chips, cereals and frozen meals could raise risk of brain damage and dementia, study finds.'

Mara: Those three share a box in a system researchers call NOVA. It sorts food into four groups by how much industrial processing went into it, and why. Not just by nutrients. Unprocessed or minimally processed food, then cooking ingredients, then processed foods, then ultra-processed.

Eli: So it measures the factory's hand, not the nutrition label.

Mara: Right, and the last group is the industrial end: formulations of many ingredients, often with additives and little intact whole food left. One researcher who has consulted for food companies points to the back of the packet, to 'chemical compounds and names of things that we wouldn't find in the ordinary domestic kitchen.'

Eli: The second scan is the first look at what one brain did with it.

Under the Scanner

Mara: The month was rough. He ate when he wanted, no force-feeding. He said he felt like he'd aged into his early fifties or sixties, aching and sleeping badly. 'I found myself being very sleepy, not concentrating so well,' he recalled. 'I was always hungry.' One account says he ate in a trance-like state, as if addicted to the food.

Eli: His blood told the same story. Satiety hormones are the body's 'that's enough' signal. After the diet, the same test meal caused, in his words, 'a very blunted rise in the satiety hormones.' And 'my hunger hormones remained high.'

Mara: A fainter stop signal, up against food that's easy to overeat. Sugar, salt and fat together, sometimes with sensory additives, make it very palatable. The researcher who consulted for the industry says companies first asked him to help cut salt, fat and sugar. Then the question became: 'How can we make these foods irresistible?'

Eli: Then the second scan. Functional MRI shows which brain areas are active together, a bit like watching which phone lines light up at once. After the month, he described 'a massive increase in connection' between habit-forming areas at the back of the brain and reward areas in the middle.

Mara: One account adds that his reward centres lit up when he thought about eating, with pathways like those of people addicted to alcohol or nicotine.

Eli: Eight weeks back on his usual diet, the change was still there. But he's precise about it: 'these changes were physiological, not structural. They're about the two bits of the brain talking to each other.' No structural changes were reported. Altered talk between regions isn't evidence of lost brain cells.

Mara: He adds his own caution: with fMRI from any experiment, it's hard to be sure what's causing what. So, one man, one month, one shifted pattern. And nothing yet about whether whole populations eating this way end up with injured brains.

The Canadian Turn

Eli: That needs scale. A Canada-wide study took 8,783 adults, none with cardiovascular disease. They were aged 35 to 69. Researchers set their diets against body fat, liver fat, brain MRIs and cognitive scores. Jules Griffin called it 'a well conducted, relatively large-scale epidemiology study.'

Mara: So not one man's connectivity, but thousands of scans looking for actual injury.

Eli: Vascular brain injury means damage from small blood vessels, like silent strokes, showing on MRI before any symptoms do. The researchers reported 40% higher adjusted odds of it in the highest-intake group than in the lowest. In some people whose diets were more than 45% processed food, they saw silent stroke alongside a pre-stroke profile. Sonia Anand put it this way: 'We observed an independent effect of the ultra-processed foods and the brain damage seen in the MRI scans.'

Mara: And yet the same people took two cognitive tests, and the study reported no significant link between intake and their scores. Injury on the scan, nothing measurable in the thinking.

Eli: Griffin's caution is about what else was on those plates. The heaviest ultra-processed eaters also ate more Calories. The authors corrected for that mathematically, along with age, sex, city, education and income. But, he said, 'mathematical corrections can be confounded, and the authors do not correct for the increased consumption of salt, sugar and saturated fat in the diet of those that consume the most UPF.'

Mara: So that 40% rides along with more salt, sugar and saturated fat, unseparated.

Eli: His reading: diet, especially calorie-dense foods higher in saturated fat, free sugar and salt, 'may contribute to poorer brain health as we age, and we need studies now to test what causes these associations.' And this was one snapshot in time. It shows the diet and the injury side by side, not which came first.

Longitudinal Risks and the Gut-Brain Axis

Mara: The longer studies do what a snapshot can't. They enrol healthy people, record what they eat, then follow them for years and count who declines or develops dementia. In Brazil, a study called ELSA-Brasil followed thousands of adults. The median follow-up was eight years. Those eating more ultra-processed food had faster declines in overall thinking, and in executive function, the brain's planning and self-control skills.

Eli: The eating was recorded first, so the order runs the right way. Order still isn't cause.

Mara: Britain's UK Biobank followed tens of thousands of older people, free of dementia at the start, for roughly a decade. Each extra 10% of ultra-processed food went with higher risk of dementia, Alzheimer's and vascular dementia included. And replacing some of it with minimally processed food went with lower risk.

Eli: Harvard Health reports an American study of older adults pointing the same way. Those eating the most had a 58% higher dementia risk than those eating the least.

Mara: Hold that against van Tulleken's month. His scans caught regions talking to each other differently; these cohorts catch populations declining over years. What links the two is still unknown. The sharper question is what, physically, could carry a diet's effect from the gut to the brain.

Eli: The leading idea starts with the gut lining. A 2026 review reports that ultra-processed diets alter gut microbes, weaken the intestinal barrier and increase immune activation. Bacterial toxins called LPS can slip into the blood flowing to the liver. The name for that leak is endotoxemia. There they switch on inflammation signalling in liver and immune cells. That's one route along what's called the gut-brain axis. Geert de Vries adds another link: 'The gut also contains branches of the vagus nerve, which forms a direct information pathway to the brain.' Liu and colleagues frame the whole chain as what may happen, not an established cause.

Mara: A side trail, kept separate. In 2020, Kathleen Holton published a study of a low-glutamate diet for pain management. It involved 40 veterans. After a month on the diet, 73% had improved symptoms.

Eli: That's pain symptoms in a small group, not ultra-processed food injuring brains.

Mara: And every pathway here starts with a bundle: sugar, fat, additives and missing fiber arriving together. Pulling processing apart from nutrients takes a different kind of experiment, Eli.

Matching the Meal

Eli: One built for exactly that. Researchers gave healthy adults meals, one highly processed, the other minimally processed. The researchers say the two were matched within 1% for calories, carbohydrates, fat, protein, water and salt.

Mara: So calories, fat and salt held level, and only the processing differs.

Eli: And the bodies still split. Insulin is the hormone that pulls sugar out of the blood. After the processed meal, the researchers measured a much higher insulin response, with blood sugar elevated for much longer. One nutrition researcher said the body uses carbs and fats differently, 'similar to what is seen during early insulin resistance (though important to note this was only one meal).'

Mara: The brain split too. Shown food pictures, regions involved in motivation and reward responded differently to highly and minimally processed foods. Same territory as van Tulleken's scans, and his fMRI caution carries over: a response shifts, but what it means stays open.

Eli: One of the matched-meal researchers says as much: 'we don't know if these short term, immediate changes are what leads to the poor health outcomes associated with ultraprocessed foods.' But the study offers 'good clues to start looking for causality.' That leaves open how van Tulleken himself weighs processing against nutrients, and whether he'd pin it all on processing.

Processing, Confounding, and the Answer

Mara: He won't. He says NOVA was built to ask, 'is there something more to harmful food than simple levels of salt, sugar, and fat?' And whether industrial food differs from home cooking once those are adjusted for. Yet he's also said salt, sugar, fat and energy density might explain maybe 80% of the harms. He'd even accept someone arguing for all of them.

Eli: Seamus Higgins, a food process engineer, goes further. He argues many effects blamed on ultra-processed food can be explained by calorie density, fiber, protein, texture and eating rate, rather than processing itself.

Mara: Underneath both sits confounding: something that travels with the food, like income, lifestyle or other illnesses, getting mistaken for the food's own effect. Studies adjust for what they can, but one team wrote that some of it 'may remain unmeasured.' Van Tulleken puts it plainly: 'association and causation are different things.'

Eli: And Sumanto Haldar notes studies adjust for different things, each with its own limits. Similar headlines can hide different gaps.

Mara: The other reading has its holders too. Sonia Anand saw an independent effect in the Canadian scans, and the matched meals moved insulin and brain responses with the main nutrients held level. On that reading, processing and additives act on gut and brain directly.

Eli: Which is why the formal judgments sit where they do. Guideline committees want trials where people are assigned a diet, because that's how cause gets tested. In 2024, the Lancet Commission on dementia found insufficient evidence that cutting ultra-processed food would help prevent dementia. In 2025, Britain's nutrition advisory committee, SACN, and the US dietary guidelines committee said the evidence was too thin to include it in guidelines. Both called for randomized trials.

Mara: And a 2026 review calls ultra-processed food 'a plausible and increasingly supported risk marker and exposure, but causal pathways remain incompletely established.' It reports links with cognitive decline, stroke and dementia, with causality still uncertain.

Eli: Here's where it lands, then. Heavy ultra-processed eating goes with vascular injury on brain scans, and with cognitive decline and dementia over years. Short experiments show the brain responding differently to it. What hasn't been shown is that the food itself directly causes long-term brain damage, or that it doesn't. That first scan made van Tulleken a baseline. A month later his brain regions were talking differently, no structural change reported, and no one can yet say what that means in the long run.

Mara: The signals to watch: long-term imaging that tells permanent injury from functional change. Feeding trials that separate additives and processing from sugar, fat, salt and calories. And imaging cohorts that explain why the Canadian scans showed injury the cognitive tests didn't.

Eli: Until then, the link shows up on the scans and in the cohorts, and the cause is still being tested.

Mara: Listeners can look into the NOVA classification framework.

Eli: Follow health with us as more stories ask whether ultra-processed diets drive lasting neurological damage.

Mara: That's where we'll leave it. I'm Mara.

Eli: And I'm Eli. Thanks for listening. Until next time on Angle.