Advances in Nutrition review finds the effect of whole-diet interventions on memory and cognitive function in healthy older adults is “modest and inconclusive.”
According to a United Nations Report, World Population Prospects 2024, “by the mid-2030s, those aged 80 and over will outnumber infants (one year of age or less).” Moreover, “by the late 2070s, the global population aged 65 and older is projected to reach 2.2 billion, exceeding the number of children under 18.” These global aging trends will be accompanied by increases in age-related memory loss and cognitive decline, including Alzheimer’s disease, which exert significant economic, societal, and personal burdens. It is therefore critical to identify lifestyle factors to prevent and reduce these disorders.
An increasing number of studies suggest that diet affects memory and cognition in healthy older adults; however, randomized, controlled trials investigating the effects of whole-diet interventions, such as the Mediterranean diet and the MIND diet, on memory and cognition in healthy older adults are rare, with conflicting results often reported.
In response, the authors of The Effect of Whole-Diet Interventions on Memory and Cognitive Function in Healthy Older Adults – A Systematic Review analyzed the findings from randomized controlled trials of whole-diet interventions, alone or in combination with other interventions, to determine “whether whole-diet interventions are a viable nonpharmacological strategy to improve or maintain cognitive function in older adults, with a specific focus on memory.” The authors believe that this review is the first to specifically focus on the effects of whole-diet interventions, as opposed to individual foods or nutrients, on memory in healthy older adults. The results of their review were published in Advances in Nutrition—An International Review Journal, a publication of the American Society for Nutrition.
To begin their research, the authors conducted a comprehensive search of the scientific literature to find randomized controlled trials that reported on whole-diet interventions among healthy adults aged 60 and older and their effect on memory and cognitive function. The dietary intervention could be given alone or as part of a multi-prong intervention, such as combinations of dietary advice and physical activity. The authors’ search led them to 23 studies based on 13 randomized controlled trials that met their criteria.
Among the results, three of the studies that investigated whole-diet interventions alone and two multiple intervention studies showed positive effects on memory function. In addition, one study that investigated whole-diet interventions and five multiple intervention studies showed positive effects on other cognitive outcomes.
Overall, however, the authors found that “the effect of randomized, controlled whole-diet interventions on memory and cognitive function in healthy older adults is modest and inconclusive.” Underlying this conclusion were several factors, including the heterogeneity of study designs under review. The studies, for example, employed a wide variety of cognitive tests, questionnaires and brain imaging measurements, which led to different findings. In addition, most of the studies under review were based on multiple interventions, thereby making it difficult to determine the particular contribution of diet to any observed effects.
The duration of the studies under review also varied greatly, ranging from four weeks to three years. Interestingly, the four-week study showed positive effects on episodic memory, whereas the three-year study showed no differences on memory between the intervention diet and the control diets: “therefore, a longer study duration does not necessarily lead to positive effects on memory and cognition.”
“To confirm the findings of cross-sectional studies and claims of popular science communications within the field of nutrition, cognition, and aging,” the authors argue that “sufficiently powered studies with memory as the primary outcome are necessary.” Moreover, “to separate the effects of different lifestyle interventions, the field needs studies isolating interventional approaches.”
