- George Wang, MD, PhD
Does diet influence the risk of developing Alzheimer’s disease?
The short answer is, “Yes,” according to a study published in the Journal of Alzheimer’s Disease that pooled results from five prior research studies (1). In this systemic review (a study of studies), people who most closely followed a Mediterranean diet had a one-third lower risk of developing mild cognitive impairment and Alzheimer’s disease, compared to people whose diet least resembled the Mediterranean diet. (Mild cognitive impairment can be roughly considered an intermediate state between healthy aging and early dementia.)
In people who were cognitively healthy, following a Mediterranean diet more closely was associated with a 27% lower risk of developing mild cognitive impairment, and a 36% lower risk of developing Alzheimer’s disease.
The caveat in interpreting these results is that they come from epidemiologic studies rather than randomized controlled trials. To say this more simply, because of the design of the research study, it’s possible that some other factors than the diet could have influenced the results, though not likely. The design that would answer the question more definitively (randomized controlled trials) is much costlier and more challenging to implement.
Results from one of the first of such randomized controlled trials looking at the effect of diet on brain health became available in April, 2018. This study, conducted in five European centers (France, Italy, the Netherlands, Poland, and the United Kingdom), randomly assigned almost 1,300 people aged 65 – 79 years who were free of dementia to two groups. One group received individually tailored advice on Mediterranean-like diets (“intervention” group). The other group followed their habitual diet (“control” group).
This trial showed that although there was no significant difference in cognitive changes between the two groups after one year, study participants who adhered closely to Mediterranean-like diets had improvements in global cognitive function and episodic memory (memory of specific events), compared to participants who did not adhere well to dietary recommendations.
So what exactly is a Mediterranean diet? It is commonly described as the diets traditionally found across the Mediterranean Sea countries. However, because such diets vary from region to region, I find that the most practical and useful way to think about the Mediterranean diet, which also happens to capture the essence of what a healthy diet should look like, is this:
Eat 1) mostly whole foods, rather than processed foods, and 2) mostly plants, rather than animal foods. (Plants include whole grains, legumes, vegetables, fruits, nuts, and seeds.)
By following these two simple principles, we automatically address other potential concerns, such as carbs (simple carbs vs. complex carbs) and unhealthy fats. Not all carbs are bad, but this is a topic for another day. When it comes to changing our eating habits, I find that simplifying the plan into easy-to-remember guidelines will make the plan much more sustainable. (Whenever you decide to make a drastic change to your dietary habits, it’s always a good idea to consult a qualified nutritionist or a clinician who is well-versed in nutrition.)
These research results are particularly important in informing a multimodal approach (a holistic approach incorporating several strategies) to the prevention and treatment of Alzheimer’s disease. Because the currently available medications for treating Alzheimer’s do not address the underlying cause of the disease, it is not surprising that these medications do not prevent or reverse the progression of dementia. Research evidence is still scarce but accumulating for an integrative medicine approach to preventing and treating Alzheimer’s disease that addresses different risk factors and lifestyle choices.
When following a healthy diet such as above (as part of a “food as medicine” approach to optimizing our cognitive health) is also associated with lower risks of many other chronic diseases, including diabetes, heart disease, and cancer, the decision to do so is almost a no-brainer.
1. Singh, B., et al., Association of mediterranean diet with mild cognitive impairment and Alzheimer's disease: a systematic review and meta-analysis. J Alzheimers Dis, 2014. 39(2): p. 271-82.