The new study has found that among people monitored after a CIS episode, those who ate more ultra-processed foods had more relapses and increases in brain lesions over time than those who ate less of these unhealthy foods.
The study results were presented at the 2025 Congress of the European Committee for Treatment and Research in Multiple Sclerosis (ECTRIMS) and have not yet been peer reviewed.
Researchers found that although a diet with more ultra-processed food didn’t ultimately affect whether someone with CIS went on to develop MS, it did appear to worsen disease activity among those who were already showing other early signs of the disease.
What this suggests is that ultra-processed foods seem to act as a chronic inflammatory accelerant, rather than a disease trigger, says the lead author, Gloria Dalla Costa, PhD, a research scientist in nutrition at the Harvard T.H. Chan School of Public Health in Boston.
“Eating more of these types of foods clearly exacerbated disease activity in people with clinically isolated syndrome,” says Dr. Dalla Costa.
Ultra-processed foods are products that go through multiple steps of industrial processing and often include additives such as preservatives, emulsifiers, and flavor enhancers.
Examples include packaged snacks, soft drinks, instant noodles, frozen meals, and processed meats like hot dogs.
Biomarkers in the Blood Can Say a Lot About Diet
The research team analyzed data from 451 people enrolled in the BENEFIT trial, which began in 2002 and followed individuals with clinical isolated syndrome for five years. Instead of relying on food diaries, the researchers used a validated “metabolomic signature” — a panel of 39 blood markers from participant samples — to estimate how much ultra-processed food each person ate.
This study is one of the first to use a blood analysis for this assessment rather than relying on self-reported food questionnaires.
“This methodology is important because diet questionnaires can be inaccurate,” says Rob Bermel, MD, the director of the Mellen Center for MS Treatment and Research at Cleveland Clinic.
Ultra-processed Foods Increase Risk of MS Relapses
Over the five-year study period, 208 participants were diagnosed with clinically definite multiple sclerosis.
By combining blood data with magnetic resonance imaging (MRI) scans and participant health outcomes, the researchers could see how dietary exposure was linked to the progression of early MS over time.
Participants who consumed the most ultra-processed foods had about 30 percent more relapses over five years than those who ate the least.
Participants in the high-consumption group also had:
- More active inflammatory lesions on MRI by year two
- Greater lesion volumes over the five-year follow-up
- Lower neurological function scores
“These findings were independent of other factors such as age, sex, body weight, vitamin D, smoking, or treatment assignment,” says Dalla Costa.
“By using blood-based metabolic markers, the study provides stronger evidence that ultra-processed foods are linked to increased inflammation in early multiple sclerosis,” says Dr. Bermel, who was not involved in the research.
Unhealthier Diets Didn’t Increase the Risk of Developing MS
A diet full of highly processed foods did not increase a participant’s risk of going from CIS to clinically definite multiple sclerosis. Instead, diet appeared to influence the severity and frequency of disease activity once symptoms had already begun.
“Our results suggest that ultra-processed foods do not cause multiple sclerosis, but they make it harder for the nervous system to withstand and repair damage,” says Dalla Costa.
That result was surprising to Bermel. “It’s possible that the study methodology may be a factor explaining these differences, which deserve further investigation,” he says.
How Ultra-processed Foods May Affect the Brain
The researchers proposed several biological explanations for why ultra-processed foods may worsen inflammation in MS.
- Gut barrier disruption: Additives such as emulsifiers may damage the lining of the gut, allowing bacterial toxins to enter the bloodstream and activate the immune system.
- Altered cell membranes: Modified fats in processed foods may change the makeup of nerve cell membranes and myelin (a protective sheath around nerves), making them more vulnerable to attack.
- Metabolic stress: Certain metabolic markers suggest reduced energy production in brain cells, which may limit the brain’s ability to repair itself after inflammation.
Questions Remain About How Diet Quality Affects MS Activity
As with any study, there are caveats. The dietary signature was measured at only one point in time, at the beginning of the trial. That means researchers don’t know whether changes in diet later on altered outcomes. The participants’ blood samples were also taken about 20 years ago — and the food landscape has changed since then, Bermel points out.
“We need to be cautious in applying results from samples collected in the early 2000s to today’s diets and food environments,” says Bermel. It’s also not clear if certain MS treatments are less effective depending on a person’s diet, he adds.
Another limitation is that while the blood signature of ultra-processed food intake is objective, it doesn’t reveal exactly which foods or additives are most harmful. “We still don’t know the specific mechanisms driving these effects,” Bermel says.
Is There a ‘Best Diet’ for MS?
“We already know from other studies that diets high in processed foods can affect brain health, including increasing risks of stroke and dementia. This research adds to that body of evidence, suggesting that food choices may also shape inflammatory activity in multiple sclerosis,” says W. Taylor Kimberly, MD, PhD, a critical care neurologist, researcher, and associate professor of neurology at Harvard Medical School in Boston. Dr. Kimberly wasn’t involved in the study.
Kimberly emphasizes that small, sustainable changes are more realistic than extreme diet overhauls. “Even incremental shifts can make a meaningful difference over time,” he says.
Bermel encourages healthy lifestyle habits for his patients with MS as well, though he cautions that it’s still unclear how much impact that has on the disease. “That’s why we view wellness strategies as an essential part of MS treatment, but not a substitute for taking a disease-modifying therapy,” says Bermel.
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