Background: The gut microbiota in healthy older individuals typically show a decrease in beneficial bacteria like Bifidobacterium and Lactobacillus, alongside an increase in pro-inflammatory microbes such as Enterobacteriaceae and Clostridia. These changes contrast with younger and middle-aged individuals and appear to correlate with cognitive status. Although there is extensive research on gut microbiota and cognitive functions in cognitively impaired elderly individuals, its impact on cognitively healthy elderly populations has not been extensively studied. Method: A comprehensive literature search was conducted across PubMed, EBSCO, Web of Science, and Scopus databases to identify studies exploring the relationship between gut microbiota composition and cognitive functioning in healthy older adults. During the literature screening process, each record was initially assessed by its title, abstract, and keywords to exclude articles that did not align with the scope of this review. Three authors independently screened and retrieved the records. The inclusion criteria included: (1) publication in peer-reviewed journals; (2) studies involving neurologically, cognitively, and medically healthy populations; (3) participants identified as older adults, defined for this review as individuals aged 45 years and older due to the limited number of records; (4) analysis of gut microbiota; and (5) assessment of cognitive function. Subsequently, full texts were analyzed to determine eligibility. The exclusion criteria encompassed: (1) incorrect publication type; (2) inappropriate sample population; (3) unsuitable study design; (4) absence of one or more inclusion criteria; and (5) studies based on animal research. A risk of bias assessment was performed for each included study using the Joanna Briggs Institute (JBI) checklist, ensuring all selected studies met established quality standards. Results: A total of 6 eligible research articles from a possible 1752 published until March 2024 were identified and included. We categorized the included studies into two groups based on their focus: the taxonomic composition of gut microbiota and the alpha diversity, which is the variety of organisms within a sample. Additionally, two methods were identified for assessing cognition: neuropsychological tests and physiological measurements, notably electroencephalography (EEG). The studies show varying results regarding the abundance of specific bacterial taxa and their cognitive associations. Notably, the relationship between certain bacteria and cognition may vary when analyzed at different taxonomic levels, such as phylum versus family. Conclusions: Changes in gut microbiota composition in the elderly, even without a cognitive impairment diagnosis, could potentially serve as early biological markers for Alzheimer’s disease or other dementias before mild cognitive impairment appears.

Background: Mood disturbances, often accompanied by cognitive deficits, represent a major public health challenge. Diet is increasingly recognized as a modifiable factor in mental health, with specific nutrients such as omega-3 polyunsaturated fatty acids (PUFAs) showing therapeutic potential. This study investigated whether dietary omega-3 intake moderates variations in cognitive performance associated with psychological symptoms in non-clinical samples. Method: A total of 313 healthy adults completed a food frequency questionnaire (FFQ) to assess dietary intake. Psychological symptoms were measured using the depression screening questionnaire (PHQ-9) and the stress assessment instrument (PSS-10), while cognitive performance, including short-term and episodic memory, was evaluated using Sternberg and Old/New recognition tests. A subgroup of 52 older adults completed a detailed in-person FFQ to enable the precise quantification of EPA, DHA, and alpha-linolenic acid (ALA) intake. Results: Diets rich in omega 3, particularly nuts, seeds, fish and seafood, were associated with lower depression and stress scores. EPA and DHA, but not ALA, were specifically linked to those mood benefits. However, dietary omega-3 intake was not significantly associated with cognitive performance and did not moderate the relationship between mood and memory. Self-reported omega-3 supplementation was linked to fewer depressive symptoms and better episodic memory. Conclusions: While dietary omega-3 is associated with improved well-being, its role in cognition in healthy adults is not well-established and warrants further investigation.