By Joseph E. Scherger, MD, MPH
Vice President, Primary Care, Eisenhower Medical Center; Clinical Professor, Keck School of Medicine, University of Southern California
Dr. Scherger reports no financial relationships relevant to this field of study.
SYNOPSIS: A controlled trial of adults 55-80 years of age showed that intake of a Mediterranean diet plus 1 liter of extra virgin olive oil each week improved or maintained cognitive function compared with controls on a low-fat diet who showed cognitive decline.
SOURCE: Valls-Pedret C, et al. Mediterranean diet and age-related cognitive decline: A randomized clinical trial. JAMA Intern Med 2015;175:1094-1103.
This is a post-hoc analysis of a study in Barcelona, Spain, examining antioxidant supplementation in a population of men 55-80 years of age and women 60-80 years of age followed between 2003 and 2009. The authors randomly assigned 447 cognitively healthy volunteers, roughly half men and women, to three groups: a Mediterranean diet plus 1 liter of extra virgin olive oil per week, a Mediterranean diet plus 30 g/week of mixed nuts (walnuts, hazelnuts, and almonds), and a low-fat diet as the control group. All of the volunteers were at high risk for cardiovascular disease, with 55% presenting with type 2 diabetes and the rest presenting with at least three of the following five risk factors: hypertension, dyslipidemia, overweight, obesity, and a family history of early onset coronary heart disease. None had active cardiovascular disease at the time of the trial.
An experienced neuropsychologist performed a battery of cognitive tests at the beginning of the study and again approximately 4 years later. The dropout rate was similar for all three groups, and 340 volunteers completed the two cognitive screenings.
The 127 volunteers who were on the Mediterranean diet plus extra virgin olive oil showed slight improvement in the cognitive tests, the 112 volunteers on the Mediterranean diet plus nuts showed no significant change, and the 97 on a low-fat diet showed some decline in their cognitive tests.
The authors concluded that in an older population, a Mediterranean diet supplemented with olive oil or nuts is associated with improved cognitive function compared with controls on a low-fat diet.
This study is small and inconclusive but does suggest two important things. First, eating healthy may preserve cognitive function. The authors did not clearly define the Mediterranean diet but we must assume it is rich in healthy vegetables, fruit, and seafood. What is not clear is the role of pasta. The amount of olive oil consumed in one group may not be practical, and it is not clear how much olive oil and nuts were part of the Mediterranean diet in either group.
The second suggestion is that low fat consumption may be associated with cognitive decline. David Perlmutter, in his well-referenced books Grain Brain and Brain Maker, underscores the importance of healthy fats in brain health. Our brain is made up of lots of cholesterol, so encourage patients to eat egg yolks.
There is much more work to be done to clarify the role of diet in improving cognitive function. The gut-brain axis is being scientifically illuminated in a way that requires medical professionals to start taking nutrition much more seriously.2,3 What is clear is that the low-fat diet recommendations of the 1970s, 1980s, and 1990s are obsolete. The Mediterranean diet appears to be one of the best candidates for a nutrition recommendation.
- Perlmutter D. Grain Brain. New York; Little, Brown and Co. 2013.
- Perlmutter D. Brain Maker. New York: Little, Brown and Co. 2015.
- Petra AI, et al. Gut-microbiota-brain axis and its effect on neuropsychiatric disorders with suspected immune dysfunction. Clin Ther 2015;37:984-995.