I’ve written numerous articles about various diets and their links to a reduced risk of cognitive decline and dementia. A new study reviews six diets that may be linked to a reduced risk of cognitive decline and dementia.

These diets share several foods: fruits and vegetables, whole grains, fish, poultry, legumes, and nuts. The classic Mediterranean diet has all of these features.

This post will examine the six diets included in the study, as well as the study itself.

The diets and dietary indices included in the study

Dietary Approaches to Stop Hypertension (DASH) — Physicians sometimes prescribe this diet to patients with high blood pressure (hypertension). DASH is based on the following foods: fruits, vegetables, low-fat milk, whole grains, fish, poultry, beans, and nuts. It recommends reducing sodium, foods and beverages with added sugars, and red meat. The diet is heart-friendly as it limits saturated and trans fat, while increasing the intake of potassium, magnesium, calcium, protein, and fiber, nutrients believed to help control blood pressure.

Healthful Plant-Based Diet Index — this index measures diets rich in healthy plant foods while limiting less healthy plant foods and animal products.

Reversed Empirical Dietary Indices for Hyperinsulinemia — this index measures diets and the associated risk of hyperinsulinemia.

Planetary Health Diet Index — this index connects dietary practices with environmental sustainability and human health, promoting a balanced diet that benefits both people and the planet.

Alternate Healthy Eating Index 2010 (AHEI-2010) — this index measures foods and nutrients associated with a lower risk of chronic diseases such as cardiovascular disease, type 2 diabetes, and certain cancers.

Reversed Empirical Dietary Indices for Inflammatory Pattern — this index is designed to assess the inflammatory potential of diet in the US population.

Diets linked to reduced risk of cognitive decline and dementia

In a study published on 23 February 2026 in JAMA Neurology, Kjetil Bjornevik, MD, PhD, Harvard T.H. Chan School of Public Health, Boston, and co-authors followed professionals in three ongoing cohorts: the Nurses’ Health Study (NHS), the Health Professionals Follow-Up Study (HPFS), and the NHSII.

The study followed nearly 160,000 health professionals with a mean age of 44. Those who followed these six dietary patterns had a lower relative risk (RR) of subjective cognitive decline when comparing the top and bottom 10% of diet adherence.

Here are the key results:

• The group that had the highest adherence to the Dietary Approaches to Stop Hypertension (DASH) diet had a 41% lower risk of cognitive decline.
• The group that had the highest adherence to the Healthful Plant-Based Diet Index had a 24% lower risk.
• Those who adhered to the Reversed Empirical Dietary Indices for Hyperinsulinemia also had a 24% lower risk.
• Those who adhered to the Planetary Health Diet Index had a 20% lower risk.
• Those who adhered to the Alternate Healthy Eating Index 2010 (AHEI-2010) had a 16% lower risk.
• Those who adhered to the Reversed Empirical Dietary Indices for Inflammatory Pattern had an 11% lower risk.
• The DASH diet had not only the lowest subjective cognitive decline risk, but the strongest relationship with higher objectively measured global cognition, with a mean z-score difference of 0.05.

Summary

I want to caution the reader that this study shows a correlation between the various diets and a lower risk of cognitive decline and dementia. This does not mean that there is a causal link.

For example, individuals who follow these diets may engage in other behaviors, like exercise and lower caloric intake, that are also linked to a lower risk of cognitive decline. They also could have received the shingles vaccine, which is also linked to a lower risk of dementia.

Identifying the various behaviors and activities that lead to a lower risk of dementia is going to be difficult without a clinical trial to show a causal relationship. Moreover, nutritional studies can be notoriously difficult to interpret — the most important factor is that diet logs rely upon the accuracy and the memory of the patient.

The takeaway is that these diets can be an additional behavioral choice that may reduce the risk of cognitive decline. It’s not a sure thing — if you choose these diets, there is no guarantee that you will not develop cognitive declines as you age.

However, the evidence is becoming more powerful with each study. These diets may have a positive impact on the quality of aging, and it may be worth it. And if you’re going to choose a diet, DASH seems to be the way to go!

Citations

• Bui LP, Pham TT, Wang F, Chai B, Sun Q, Hu FB, Lee KH, Guasch-Ferre M, Willett WC. Planetary Health Diet Index and risk of total and cause-specific mortality in three prospective cohorts. Am J Clin Nutr. 2024 Jul;120(1):80-91. doi: 10.1016/j.ajcnut.2024.03.019. Epub 2024 Jun 10. PMID: 38960579; PMCID: PMC11251201.
• Chen H, Cortese M, Flores-Torres MH, Tessier AJ, Wang DD, Kang JH, Eliassen AH, Stampfer M, Ascherio A, Willett W, Yuan C, Bjornevik K. Dietary Patterns and Indicators of Cognitive Function. JAMA Neurol. 2026 Feb 23:e260062. doi: 10.1001/jamaneurol.2026.0062. Epub ahead of print. PMID: 41729538; PMCID: PMC12931470.
• Reyneke GL, Lambert K, Beck EJ. Food-based indexes and their association with dietary inflammation. Adv Nutr. 2025 Apr;16(4):100400. doi: 10.1016/j.advnut.2025.100400. Epub 2025 Mar 4. PMID: 40043850; PMCID: PMC11992388.
• Shivappa N, Hebert JR, Kivimaki M, Akbaraly T. Alternative Healthy Eating Index 2010, Dietary inflammatory index and risk of mortality: Results from the Whitehall II cohort study and meta-analysis of previous DII and mortality studies – CORRIGENDUM. Br J Nutr. 2017 Oct;118(8):639. doi: 10.1017/S0007114517002719. Erratum for: Br J Nutr. 2017 Aug;118(3):210-221. doi: 10.1017/S0007114517001908. PMID: 29056107.

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