A large Harvard-led study comparing six popular dietary patterns has found that the DASH diet may offer the strongest protection for brain health with aging. The findings challenge the widespread assumption that Mediterranean-style diets are always the best option for preserving cognitive function.
DASH, short for Dietary Approaches to Stop Hypertension, was developed in the 1990s to lower blood pressure and is endorsed by leading cardiovascular health organizations. The diet emphasizes fruits, vegetables, whole grains, nuts, legumes, and low-fat dairy products while limiting sodium, red and processed meats, added sugars, and alcohol.
How the Brain Diet Study Was Conducted
Researchers followed 159,347 adults for up to 30 years, repeatedly assessing their dietary habits and how closely they adhered to six well-established dietary patterns. Participants also reported changes in memory and thinking over time, while a subgroup completed objective cognitive assessments later in life.
Each participant received adherence scores for several dietary patterns, including DASH, a Mediterranean-style diet index, a healthy plant-based diet index, and a planetary health diet. The researchers then compared these scores with the likelihood of subjective cognitive decline and performance on standardized cognitive tests.
DASH Shows the Strongest Association
All six dietary patterns were associated with better cognitive outcomes, but DASH demonstrated the strongest relationship. Participants in the highest 10% of DASH adherence had a 41% lower likelihood of subjective cognitive decline than those in the lowest 10%, even when dietary habits had been assessed decades earlier.
Individuals with the highest adherence to DASH also performed better on objective cognitive testing, demonstrating global cognitive function equivalent to being approximately 0.76 years younger and working memory equivalent to being 1.37 years younger. The association was particularly strong among participants who followed the diet during midlife, between the ages of 45 and 54 years.
How Other Diets Compared
Two additional dietary patterns—a healthy plant-based diet index and a low-hyperinsulinemia dietary index—were each associated with a 24% lower risk of subjective cognitive decline. A planetary health diet, which places greater restrictions on red meat consumption, was associated with a 20% lower risk.
A Mediterranean-style dietary pattern known as the Alternative Healthy Eating Index 2010 (AHEI-2010), which is frequently promoted for brain health, was associated with a 16% lower risk among participants with the highest adherence. Although this association remained beneficial, it was weaker than that observed for the DASH diet in this study population.
What This Means for Dementia Risk
The study, published in JAMA Neurology, was observational and therefore cannot establish a direct causal relationship between diet and dementia prevention. Nevertheless, it adds to a growing body of evidence suggesting that dietary habits influence brain aging and may affect the risk of Alzheimer’s disease and related dementias.
Previous studies of hybrid dietary approaches, such as the MIND diet—which combines key elements of both the DASH and Mediterranean diets—have demonstrated fewer dementia-related pathological brain changes at autopsy among individuals with high dietary adherence. In contrast, processed red meat and diets high in added sugars have consistently been associated with poorer cognitive outcomes.
Practical Takeaways for Healthy Eating
Experts emphasize that the key message is not that a single dietary pattern is universally superior but rather that eating patterns rich in vegetables, fruits, whole grains, legumes, nuts, and fish, while limiting processed meats, fried foods, and sugar-sweetened beverages, appear to support healthy brain aging. Many of the same dietary choices that benefit cardiovascular health also appear to protect cognitive function.
Lead author Kjetil Bjornevik notes that gradual, sustainable dietary changes are most likely to be maintained over time. Practical examples include reducing sodium intake, choosing whole grains instead of refined grains, and replacing processed meats with fish or plant-based protein sources. Over many years, these relatively small adjustments may contribute to measurable improvements in long-term brain health.
Randomized clinical trials and studies involving larger and more diverse populations will be necessary to determine whether DASH or similar dietary patterns can directly reduce the incidence of dementia. For now, the findings reinforce current recommendations that dietary habits supporting cardiovascular health may also represent one of the most effective strategies for preserving cognitive health throughout aging.
