Medscape... JAMA Intern Med. Published online May 11, 2015. Abstract Adding nuts and olive oil to a Mediterranean diet could protect cognitive function in older adults, new research suggests.
The study showed that adding nuts to the Mediterranean diet boosted measures of memory, while supplementing the diet with extra-virgin olive oil improved global and frontal cognition.
The results suggest that nutritional interventions to protect brain function should be started "at the preclinical stage, before any impairment," even in older adults, said study author Emilio Ros, MD, PhD, consultant, Endocrinology Department, Hospital Clinic, Barcelona, Spain. Dr Emilio Ros
"Our participants were cognitively healthy to start with. We believe that if they had been cognitively impaired, we wouldn't have seen any effect."
The study was published online May 11 in JAMA Internal Medicine.
PREDIMED Study
The analysis was conducted on a subcohort of the Prevención con Dieta Mediterránea (PREDIMED), a 5-year randomized clinical trial of nutrition intervention, the main analysis of which was previously published in the New England Journal of Medicine. PREDIMED compared the cardiovascular effect of the Mediterranean diet with added mixed nuts or olive oil, and a control diet that encouraged reduced dietary fat, in older adults at high cardiovascular risk.
The study participants had type 2 diabetes or at least three of five cardiovascular risk factors: smoking, hypertension, dyslipidemia, overweight or obesity, and family history of early-onset coronary heart disease.
The current analysis looked at the effect of the diets on cognition. It included 127 participants in a receiving a Mediterranean diet plus olive oil, 112 in a group receiving a Mediterranean diet plus nuts, and 95 in a control group. The mean age of participants was 66.8 years, and 50.9% were women.
Those in the olive oil group received 1 L of olive oil per week. Those in the nuts group got 30 g of mixed nuts per day (walnuts, hazelnuts, and almonds). The control group was given advice to reduce their dietary fat.
The study participants were seen quarterly. (The control group was seen annually for the first 3 years of the trial, but the protocol was changed to annual visits because the more infrequent visits could be considered a limitation of the trial
Adding nuts and olive oil to a Mediterranean diet could protect cognitive function in older adults, new research suggests.
The study showed that adding nuts to the Mediterranean diet boosted measures of memory, while supplementing the diet with extra-virgin olive oil improved global and frontal cognition.
The results suggest that nutritional interventions to protect brain function should be started "at the preclinical stage, before any impairment," even in older adults, said study author Emilio Ros, MD, PhD, consultant, Endocrinology Department, Hospital Clinic, Barcelona, Spain. Dr Emilio Ros
"Our participants were cognitively healthy to start with. We believe that if they had been cognitively impaired, we wouldn't have seen any effect."
The study was published online May 11 in JAMA Internal Medicine.
PREDIMED Study
The analysis was conducted on a subcohort of the Prevención con Dieta Mediterránea (PREDIMED), a 5-year randomized clinical trial of nutrition intervention, the main analysis of which was previously published in the New England Journal of Medicine. PREDIMED compared the cardiovascular effect of the Mediterranean diet with added mixed nuts or olive oil, and a control diet that encouraged reduced dietary fat, in older adults at high cardiovascular risk.
The study participants had type 2 diabetes or at least three of five cardiovascular risk factors: smoking, hypertension, dyslipidemia, overweight or obesity, and family history of early-onset coronary heart disease.
The current analysis looked at the effect of the diets on cognition. It included 127 participants in a receiving a Mediterranean diet plus olive oil, 112 in a group receiving a Mediterranean diet plus nuts, and 95 in a control group. The mean age of participants was 66.8 years, and 50.9% were women.
Those in the olive oil group received 1 L of olive oil per week. Those in the nuts group got 30 g of mixed nuts per day (walnuts, hazelnuts, and almonds). The control group was given advice to reduce their dietary fat.
The study participants were seen quarterly. (The control group was seen annually for the first 3 years of the trial, but the protocol was changed to annual visits because the more infrequent visits could be considered a limitation of the trial).
"We didn't dare put too much fat in a study arm," he said. "We also worried there wouldn't be as much compliance if participants were asked to add both nuts and olive oil."
"Modest" Results
Asked to comment, David Knopman MD, professor of neurology at the Mayo Clinic College of Medicine in Rochester, Minnesota, doing research in late-life cognitive disorders, noted some of the study's strengths, including the "good but not great" sample sizes, the duration of follow-up, and the fact that it appears to be the only such randomized, controlled trial of the Mediterranean diet aside from the parent PREDIMED study.
However, said Dr Knopman, the results were "very, very modest." On nine test scores, there were three changes that "barely met the P less than .05 criteria, apparently mainly due to the Mediterranean diet plus olive oil treatment," he said.
Dr Knopman also noted other "real weaknesses" of the trial. For example, the dropout rate was high (although the higher rate in the untreated group would seem to favor the Mediterranean diet groups) and it was of necessity unblinded.
But his greatest concern is not knowing the proportion of participants who actually adhered to the diet. "The authors provide only group means in the article, which is not adequate. What if only 50% of participants actually used the olive oil or nuts?"
Dr Knopman said that he recognizes the challenges in conducting this type of analysis. For example, in starting with cognitively healthy people, the study was almost certainly underpowered to see an effect on cognition.
The study should be viewed with "great caution," stressed Dr Knopman. Although it's much better than purely observational studies, it is far from providing definitive evidence, he said.
"Personally, I believe that the scientific community has compromised its reputation with the lay public with the conflicting dietary claims and counterclaims that have hit the mainstream media. A prudent approach would be to say that the definitive studies have yet to be done."
Combining fundamentally weak empiric data with scientifically sounding claims such as "antioxidant," "cerebrovascular blood flow," and "modulation of neuronal signaling" is not good science but "a lot of smoke and mirrors," added Dr Knopman.
"The common-sense notions of a healthy diet that lacks gimmicks ought to be the default until strong evidence to the contrary emerges."
Dr Ros reports receiving research funding and is a nonpaid member of the scientific advisory committee of the California Walnut Commission. Dr Knopman has disclosed no relevant financial relationships.