The Mediterranean diet is considered a gold standard eating pattern thanks to the numerous health benefits associated with it. The diet, which emphasizes whole plant foods and extra virgin olive oil, has been tied to a lower risk of Type 2 diabetes, heart disease, stroke, depression and breast cancer.
Many studies have also suggested that a Mediterranean-style diet helps guard against cognitive decline and dementia.
Now, new study findings cast doubts about the diet’s potential cognitive benefits. The research, published Oct. 12 online in the journal Neurology, suggests that following a Mediterranean diet in midlife doesn’t reduce the future risk of dementia.
The latest findings
The study, which spanned 20 years, examined whether adherence to conventional dietary guidelines or to a Mediterranean diet lowered the future risk of dementia, including Alzheimer’s dementia and vascular dementia, the two most common types.
At study’s outset, researchers collected dietary, lifestyle, health and demographic data from 28,025 participants, average age 58, who were enrolled in a continuing health study in Sweden, the Malmo Diet and Cancer Study.
Participants filled out seven-day food diaries and a detailed food frequency questionnaire. They also completed a 45- to 60-minute interview to provide additional diet details.
The researchers then scored how well each participant’s diet matched conventional dietary guidelines and a modified Mediterranean diet.
By the end of the 20-year study, 6.9 per cent of participants (1,943) had developed dementia.
Compared to people who had poor adherence to conventional dietary guidelines, individuals with best adherence did not have a lower risk of developing all-cause dementia, Alzheimer’s dementia or vascular dementia.
High adherence to a modified Mediterranean diet was also not associated with a lower risk of dementia, including Alzheimer’s and vascular dementia.
The researchers accounted for age, sex, education, physical activity, smoking, alcohol use, daily calorie intake and body mass index, other factors that could influence dementia risk.
Strengths, limitations
The study can be credited for its large sample size, long follow-up period and use of multiple methods to collect dietary data.
One limitation, however, is that dietary data was collected only at the beginning of the study. It’s not known if participants’ food habits changed during the study.
Dietary information may also have been misreported owing to difficulty remembering food intake from the past.
As well, the diagnosis of dementia was not based on specific cognitive testing. Instead it was obtained from a national patient registry, which could possibly underestimate dementia cases.
Comparison to previous studies
A review of 64 studies, published in 2017, concluded that adhering to a Mediterranean diet may slow cognitive decline and lower the risk of developing dementia.
The researchers of the current Swedish study, however, noted several weaknesses in many of these previous studies. These included relying exclusively on recall of diet from years ago, short follow-up periods and including participants older than 70, with possible cognitive impairment that had already affected their diet.
A 2019 study that followed 10,308 participants for 25 years found no link between dementia risk and the quality of midlife diet or a Mediterranean diet.
An Australian study, also published in 2019, found that MIND (Mediterranean-DASH Intervention for Neurological Delay) diet, but not the Mediterranean diet, was associated with a lower risk of cognitive impairment over 12 years.
The MIND diet, which is the most evidence-based brain health diet, is a hybrid of the Mediterranean and DASH (Dietary Approaches to Stop Hypertension) diets. It also provides daily and weekly recommendations for specific foods thought to protect the brain from inflammation and oxidative stress (e.g., berries, leafy greens, fish, beans and lentils, nuts, whole grains, extra virgin olive oil).
As well, the MIND diet gives limits for foods that can harm brain health such as red and processed meats, cheese, butter and hard margarine, fried foods and sweets and pastries.
Diet not a singular factor
Despite conflicting findings for the Mediterranean diet and dementia risk, diet still matters when it comes to protecting against cognitive decline.
According to an editorial that accompanied the latest study, diet in isolation may not have a strong enough effect on cognition. It is more likely, however, “to be considered as one factor embedded with various others, the sum of which may influence the course of cognitive function”.
In other words, a brain-healthy diet must be combined with other measures – e.g., getting regular exercise, not smoking, drinking alcohol in moderation, protecting cardiovascular health, being socially active – to have substantial benefits.
Leslie Beck, a Toronto-based private practice dietitian, is director of food and nutrition at Medcan. Follow her on Twitter @LeslieBeckRD.
Leslie Beck