Researchers studied over 200,000 people in the UK to understand how the types of carbohydrates we eat might affect our chances of developing dementia. They found that eating foods with a lower glycemic index (foods that don’t spike blood sugar as quickly) may help protect your brain, while eating large amounts of carbohydrates that raise blood sugar quickly might increase dementia risk. This is one of the largest studies to look at this connection, and it suggests that paying attention to not just what carbs you eat, but how they affect your blood sugar, could be important for brain health as you age.

The Quick Take

  • What they studied: Whether the type and amount of carbohydrates people eat affects their risk of developing dementia, including Alzheimer’s disease
  • Who participated: Over 202,000 people in the UK who didn’t have dementia at the start of the study, tracked for several years to see who developed dementia
  • Key finding: People who ate foods with a high glycemic index (foods that quickly raise blood sugar) had about 14% higher risk of dementia. Foods with lower glycemic index appeared to offer protection against brain decline
  • What it means for you: Choosing carbohydrates that don’t spike your blood sugar—like whole grains, vegetables, and legumes instead of refined sugars and white bread—may help protect your brain health. However, this is one study and more research is needed before making major diet changes

The Research Details

This was a prospective cohort study, which means researchers followed the same group of people over time to see what happened to them. They started with 202,302 people from the UK Biobank (a large health database) who didn’t have dementia when they joined. Researchers asked people about their diet using an online questionnaire and calculated two measurements: glycemic index (GI), which measures how quickly different foods raise blood sugar, and glycemic load (GL), which measures both the quality and quantity of carbs eaten. Then they tracked these people for several years to see who developed dementia and compared their diets to their health outcomes.

The researchers used advanced statistical methods to look for patterns in the data, including checking whether the relationship between diet and dementia risk was straight or curved (meaning it might change at certain points). They also adjusted their results to account for other factors that might affect dementia risk, like age, exercise, smoking, and overall diet quality.

This type of study is valuable because it follows real people in their everyday lives rather than testing them in a lab, making the results more applicable to how people actually live.

Understanding which dietary factors affect dementia risk is important because dementia is a growing health problem worldwide, and there’s no cure yet. If certain foods or eating patterns can help prevent or delay dementia, this could help millions of people maintain their brain health. This study is particularly valuable because it looked at a very large group of people and examined different types of dementia, not just one kind

This study has several strengths: it included over 200,000 people (a very large sample), followed them for years, and was published in a respected scientific journal. However, the study relied on people remembering what they ate, which can be inaccurate. Also, people who participate in health studies like this tend to be healthier than average, so results might not apply equally to everyone. The study shows association (connection) but not necessarily that diet directly causes changes in dementia risk

What the Results Show

The main finding was that the relationship between glycemic index and dementia risk followed an unusual pattern—protection at lower levels, then increased risk at higher levels. When people’s glycemic index was very high (above 49.3), they had about 14.5% higher risk of developing dementia compared to people with lower glycemic index values. This pattern held true for Alzheimer’s disease and vascular dementia (a type caused by blood vessel problems in the brain).

For glycemic load (the total amount of carbs that affect blood sugar), the pattern was similar: very high loads (above 111) were associated with increased dementia risk. This suggests that both eating foods that quickly raise blood sugar AND eating large amounts of carbohydrates that do this are problematic for brain health.

The researchers found that about 0.89 cases of dementia occurred per 1,000 people per year in their study group. While this might sound small, across a large population it represents many cases that might potentially be prevented with dietary changes.

The protective effect of lower glycemic index diets appeared consistent across different types of dementia studied, suggesting this isn’t just about one specific brain disease but about overall brain health.

The study found similar patterns for both Alzheimer’s disease (the most common type of dementia) and vascular dementia (caused by blood vessel problems). This suggests that how carbohydrates affect blood sugar might influence brain health through multiple different pathways. The researchers also noted that the relationship wasn’t simply ’lower is always better’—there was a sweet spot where risk was lowest, and both very low and very high glycemic index values showed increased risk, though the high end showed the strongest effect

Previous research has suggested that blood sugar control and insulin resistance (when the body doesn’t respond well to insulin) are linked to dementia risk. This study builds on that work by specifically examining glycemic index and load, which are practical measures of how foods affect blood sugar. Some earlier studies looked at type 2 diabetes and dementia, but this is one of the largest studies to specifically examine glycemic index and load in relation to different dementia types

The study has several important limitations. First, it relied on people reporting what they ate, which can be inaccurate—people might forget foods or misremember portion sizes. Second, the study participants were volunteers from the UK Biobank, who tend to be healthier and more health-conscious than the general population, so results might not apply equally to everyone. Third, while the study found an association between diet and dementia risk, it cannot prove that diet directly causes dementia—other unmeasured factors could be involved. Finally, the study was observational, meaning researchers watched what happened naturally rather than randomly assigning people to different diets, which is the gold standard for proving cause and effect

The Bottom Line

Based on this research, consider choosing carbohydrates that have a lower glycemic index: whole grains instead of white bread, beans and legumes instead of refined carbs, and plenty of vegetables. This recommendation has moderate confidence because while this study is large and well-designed, it shows association rather than definitive proof. It’s also consistent with general healthy eating guidelines. Talk to your doctor before making major diet changes, especially if you have diabetes or other health conditions

This research is most relevant for people concerned about brain health and dementia prevention, particularly those with family history of dementia, people with diabetes or prediabetes, and anyone over 50. It’s also relevant for people trying to make dietary choices that support overall health. However, this study doesn’t mean people need to eliminate carbohydrates—it’s about choosing better quality carbs. People with certain medical conditions should consult their doctor before changing their diet

Brain health changes happen slowly over years and decades. You wouldn’t expect to notice changes in memory or thinking in days or weeks. However, blood sugar control can improve within days to weeks of dietary changes, which is one way diet might eventually protect the brain. Any benefits for dementia prevention would likely take years to become apparent

Want to Apply This Research?

  • Track your daily glycemic load by logging carbohydrate foods and noting their glycemic index values. Aim to keep daily GL below 111 (the threshold identified in this study). Use the app to calculate GL based on portion sizes and food types
  • Replace three high-glycemic foods you eat regularly with lower-glycemic alternatives: swap white bread for whole grain, sugary cereals for oatmeal, or white rice for brown rice. Track these swaps in the app to see your GL decrease
  • Weekly review of average glycemic load trends. Set a goal to keep GL below 111 daily. Monitor energy levels and mental clarity as secondary indicators. If you have access to blood sugar testing, track fasting glucose monthly to see if dietary changes improve blood sugar control

This research shows an association between glycemic index, glycemic load, and dementia risk, but does not prove that diet directly causes dementia. This study cannot replace personalized medical advice. If you have concerns about dementia risk, diabetes, or are considering significant dietary changes, please consult with your healthcare provider or a registered dietitian. This information is for educational purposes and should not be used as a substitute for professional medical diagnosis or treatment. Individual results may vary based on genetics, overall lifestyle, and other health factors not measured in this study.