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A diet high in ultra-processed foods upped the risk of cognitive impairment or stroke, data from the prospective REGARDS study showed.

However, risk of either cognitive decline or stroke fell for people who had higher intake of unprocessed or minimally processed foods, reported W. Taylor Kimberly, MD, PhD, of Harvard Medical School in Boston, and co-authors.

A 10% increase in relative intake of ultra-processed foods raised the risk of cognitive impairment by 16% (HR 1.16, P=1.01 × 10⁻⁵) and stroke by 8% (HR 1.08, P=1.12 × 10⁻²), Kimberly and co-authors wrote in . A 10% increase in unprocessed or minimally processed foods reduced cognitive impairment risk by 12% (HR 0.88, P=1.83 × 10⁻⁴) and stroke risk by 9% (HR 0.91, P=2.13 × 10⁻⁴).

The effect of ultra-processed foods on stroke risk was greater among Black versus white participants (HR 1.15, P=1.50 × 10⁻²), the researchers found.

The two most common neurologic conditions that lead to impaired brain health are stroke and cognitive decline, Kimberly noted. "We knew from our prior studies, and studies published by other groups, that diet had an impact on both of these outcomes," he told MedPage Today.

But those studies focused on eating patterns like the Mediterranean, DASH, and MIND diets, Kimberly pointed out. "We reasoned that it's not only the type of food that matters, but also how it's processed," he said.

The study assessed four food categories based on the : NOVA1 (unprocessed or minimally processed foods), NOVA2 (processed culinary ingredients), NOVA3 (processed foods), and NOVA4 (ultra-processed foods).

Unprocessed or minimally processed foods included cut, chilled, or frozen vegetables and fruit; cuts of poultry, fish, or meat; dried or fresh pasta; grains; legumes; eggs; dried fruit; unsalted nuts and seeds; fresh or dried herbs and spices; milk or yogurt without added sugar; and coffee, tea, or water.

Ultra-processed foods were industrial formulations made from substances extracted from foods or food constituents, or synthesized in labs from food substrates or other organic sources. These included prepared meat, fish, vegetables, pizza, pasta dishes, burgers, hot dogs, energy drinks, chocolate milk, flavored yogurts, and packaged bread, cereals, cakes, cookies, and other snacks.

The researchers studied two groups from the study: 14,175 participants without evidence of cognitive impairment at baseline (cognitive impairment cohort), and 20,243 participants without a history of stroke (stroke cohort). REGARDS is a longitudinal study of stroke risk in U.S. Black and white adults; about 33% of the stroke cohort was Black.

Participants were ages 45 and older when they enrolled from 2003 to 2007. Incident stroke cases were adjudicated by medical records through September 2020, and incident cognitive impairment cases were adjudicated by follow-up cognitive testing through September 2021.

During the follow-up period, 1,108 people had strokes and 768 people were diagnosed with cognitive impairment. Associations between ultra-processed food intake and cognitive impairment or stroke were independent of adherence to the Mediterranean, DASH, and MIND diets, Kimberly and co-authors said.

The study highlights the "significant role of food processing levels and their relationship with adverse neurologic outcomes, independent of conventional dietary patterns," noted Peipei Gao, MS, of the Harvard T.H. Chan School of Public Health in Boston, and Zhendong Mei, PhD, of Harvard Medical School, in an .

"The mechanisms underlying the impact of ultra-processed foods on adverse neurologic outcomes can be attributed not only to their nutritional profiles -- poor nutrient composition and high glycemic load, which may cause metabolic dysregulation (e.g., obesity, hypertension, dyslipidemia, and type 2 diabetes), thus promoting vascular dysfunction -- but also to the presence of additives including emulsifiers, colorants, sweeteners, and nitrates/nitrites, which have been associated with disruptions in the gut microbial ecosystem and inflammation," the editorialists wrote.

The REGARDS cohort is enriched with participants from a region with high stroke prevalence, Gao and Mei observed. "Intriguingly, the study revealed the heterogeneity in the link between ultra-processed foods and stroke risk, with a stronger association observed among Black participants, which is an avenue for further study," they noted.

The research had several limitations: food intake was self-reported, and the study's observational nature precluded causal conclusions. Nonetheless, the study provides a reason to be mindful of the food we eat, Kimberly said.

"It's important to acknowledge that ultra-processed foods are convenient, tend to have a longer shelf life, and are designed to appeal to our sense of taste," he pointed out.

But incrementally lower consumption of ultra-processed foods was associated with a better brain health profile, Kimberly noted: "Because diet patterns and brain health are a long-term relationship, it may make sense to aim for small changes that are sustainable over time, rather than dramatic changes that can be hard to maintain."

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