The quality of carbohydrates in the diet may be linked to long-term brain health, according to a large observational study that followed more than 200,000 adults in the United Kingdom for over a decade.
In the study, published in the International Journal of Epidemiology, researchers found that diets with a lower glycemic index were associated with a lower risk of developing dementia, including Alzheimer’s disease. By contrast, higher-glycemic diets were associated with a modestly increased risk.
The analysis drew on data from the U.K. Biobank and included adults who did not have dementia at the start of the study. Participants completed detailed dietary questionnaires, which researchers used to estimate the glycemic index and glycemic load of their usual diets. The participants were then followed for an average of just over 13 years.
During that time, 2,362 people developed dementia. After accounting for factors such as age, sex, lifestyle and overall health, the researchers found that people whose diets fell into the low-to-moderate glycemic index range had a 16% lower risk of developing Alzheimer’s disease compared with those consuming higher-glycemic diets. Higher glycemic index values were associated with a roughly 14% higher risk.
The glycemic index reflects how quickly carbohydrate-containing foods raise blood glucose levels after eating. Foods with a higher glycemic index tend to produce sharper rises in blood sugar, while lower-glycemic foods lead to a slower, more gradual response.
In everyday diets, lower-glycemic carbohydrates are often found in foods such as whole grains, legumes and many fruits, while higher-glycemic carbohydrates are more common in refined grains and certain starchy foods.
“These results indicate that following a diet rich in low-glycemic-index foods, such as fruit, legumes or whole grains, could decrease the risk of cognitive decline, Alzheimer’s and other types of dementia,” said Mònica Bulló, the study’s senior author and a professor in the Department of Biochemistry and Biotechnology at Universitat Rovira i Virgili.
The researchers emphasized that the study does not prove that carbohydrate quality directly prevents dementia. Rather, it highlights an association between long-term dietary patterns and brain health. Glycemic index is also influenced by how foods are prepared, combined in meals and metabolized by individuals, meaning it should be interpreted as part of an overall eating pattern rather than a strict ranking of “good” and “bad” foods.
Still, the findings add to growing evidence linking metabolic health and cognitive aging. Diets that promote steadier blood glucose levels may support brain health over time, potentially through effects on insulin sensitivity, inflammation and vascular function.
The authors noted that carbohydrates make up a substantial share of total energy intake in most diets. Paying attention not only to the amount of carbohydrates consumed but also to their quality may therefore be an important consideration in strategies aimed at supporting healthy aging.
Funding information was not available.