Diet linked to cognitive function in older adults via gut microbiota

Greater adherence to dietary patterns that are beneficial to gut microbiota is associated with better cognitive function in older adults, according to data from the US National Health and Nutrition Examination Survey (NHANES). When these findings were validated in an independent Hong Kong osteoporosis cohort, higher dietary fibre intake significantly correlated with higher cognitive scores in older adults in Hong Kong.

The study, led by researchers from Hong Kong’s Microbiota I-Center (MagIC) and the Chinese University of Hong Kong (CUHK), examined the relationship between Dietary Index for Gut Microbiota (DI-GM), comprising beneficial (eg, fermented dairy, whole grains, fibre, green tea) and unfavourable (eg, red and processed meats, refined grains) components, and cognitive function in older adults (age ≥60 years) using NHANES data (final analytical sample, n=2,446). The findings were validated in an independent Hong Kong osteoporosis cohort of older adults (n=252; mean age, 87.1 years; female, 53.6 percent) with dietary records, cognitive assessments, and faecal metagenomic sequencing data, to assess microbiota’s mediating role in diet–cognition relationship. [J Prev Alzheimers Dis 2025;doi:10.1016/j.tjpad.2025.100319]

“The microbiota-targeted design [of DI-GM] provides a unique tool to investigate how diet influences cognition through the gut-microbiota–brain axis. Higher DI-GM scores, reflecting greater adherence to its microbiota-beneficial components, have been linked to reduced risk of brain diseases such as depression and stroke. However, its association with cognitive function remains unexplored,” wrote the researchers. [Eur Arch Psychiatry Clin Neurosci 2025;275:1037-1048; Food Funct 2025;16:1458-1468]

The Hong Kong osteoporosis cohort was divided into three groups: healthy controls (HC; n=125), participants with mild cognitive impairment (MCI; n=69), and participants with dementia (DEM; n=58). Participants in the DEM group were older (mean age, 89.6 years) and had a higher proportion of females (75.9 percent) compared with the HC (44.0 percent) and MCI (52.2 percent) groups. Dietary fibre intake was highest in HC (14.5 g) and lowest in the DEM group (11.1 g), while refined grains intake was highest in the MCI group (340.9 g) and lowest in the DEM group (269.6 g).

After further adjustment for age, sex, race, educational level, marital status, poverty income ratio, smoking status, drinking status, body mass index, hypertension, diabetes mellitus, and hyperlipidaemia, higher DI-GM was significantly associated with better performance on Digit Symbol Substitution Test (odds ratio, 0.90; 95 percent confidence Interval [CI], 0.82–0.99; p=0.033) in the NHANES participants.

Given the significant associations between dietary fibre and refined grains and cognitive function observed in the NHANES cohort, the researchers further validated their associations in the Hong Kong osteoporosis cohort using linear regression analysis. After adjusting for covariates, dietary fibre intake was significantly positively associated with overall score of the Hong Kong version of Montreal Cognitive Assessment (HK-MoCA) and four individual cognitive domains, namely, visuospatial/executive, language, memory, and orientation (all p<0.05), and increased abundance of fermenting bacteria. Among these species, Eubacterium siraeum and Eubacterium ventriosum were also significantly positively associated with cognitive function, including HK-MoCA and its individual language and delayed recall domains.

“Bayesian causal mediation analysis results indicated that dietary fibre was associated with a reduced risk of dementia, through both direct and indirect effects mediated by Eubacterium ventriosum, accounting for approximately 12.7 percent of the total effect,” reported the researchers.