Currently, there is an increasing number of people with mild cognitive (MCI) impairment and dementia (D). In the present work we studied the role of tau protein, β-amyloid, LPS (lipopolysaccharide), and curli protein of elderly adults with MCI or D and the contribution of gut microbiota. Four groups were studied: young subjects, healthy adults older than 60 years (A), elderly adults with MCI (MCI), and elderly adults with dementia (D). A preclinical study was conducted in old male Wistar rats to evaluate the impact of gut microbiota on curli protein abundance in feces and brain. The results showed that with increasing age, tau protein, β-amyloid, and LPS significantly increased in serum during MCI and D, and this was associated with an increase in the abundance of E. coli that synthesize the amyloid protein curli, that may promote the aggregation of amyloid proteins. Rats showed a clear increase in the abundance of curli protein in the brain during aging. Thus, cognitive impairment and dementia are in part due to an alteration in the gut microbiota–brain axis via increase in curli protein and LPS leading to an increase in tau and β-amyloid protein.

Background/Objectives: Diet–microbiota interactions shape ageing; however, their sex-specific dimensions remain poorly defined. Human studies rarely stratify analyses by sex, while most evidence of sex-dependent microbial and metabolic responses comes from preclinical models. This review synthesizes current findings on the sex-specific pathways linking diet, microbiota, and healthy ageing. Methods: A narrative review was conducted by integrating human observational studies, randomized controlled trials, and mechanistic animal research. Evidence was organized into four domains: (1) age-related changes in gut microbial composition; (2) microbiota-derived metabolites; (3) dietary patterns and functional nutrients; and (4) sex-specific endocrine and immunometabolism interactions influenced by the gut microbiota. Results: Ageing is characterized by dysbiosis, loss of short-chain fatty acid (SCFA)-producing taxa, expansion of Proteobacteria, and reduced production of key metabolites including butyrate, indoles, and polyamines. Dietary fiber, polyphenols, omega-3 fatty acids, and plant-based proteins help restore these pathways and mitigate inflammaging. Sex differences persist into later life: women show reduced estrobolome activity and SCFA decline after menopause, whereas men display higher levels of pro-atherogenic metabolites such as trimethylamine N-oxide (TMAO). Nutritional interventions, probiotics, and microbial metabolites exhibit sex-dependent responses in both human and animal studies. Conclusions: Diet–microbiota interactions shape ageing outcomes through sex-specific metabolic, hormonal, and immunological pathways. Incorporating sex as a biological variable is essential for developing personalized, nutrition-based strategies to support healthy ageing.

Background/Objectives: The purpose of this study was to evaluate the nutrient compo-sition of selected arthropods (insects and crustaceans) and lentil, and to investigate their effects as dietary protein sources on gut microbiota, host metabolism, and associated metabolites. Methods: A total of 63 male Wistar rats were randomly assigned to eight experimental groups and fed diets adjusted to 20% protein from different sources: control (C), cricket (CR), acocil (AC), chinicuil (CHI), beef (B), picanha (P), egg (E), and lentil (L). Diets were administered for 45 days. At the end of the intervention, serum was collected to assess biochemical parameters and microbiota-derived metabolites, liver samples were obtained for histological analysis, and feces were collected for intestinal microbiota pro-filing. Results: Nutritional analysis revealed that L, CR, AC, and CHI contained signif-icantly lower concentrations of choline, carnitine, and phosphatidylcholine—precursors of trimethylamine-N-oxide—than animal-derived sources (E, B, P). CHI was enriched in oleic acid, CR in linolenic acid, and L in linoleic acid, while L also displayed significantly lower cholesterol levels than E. CR, AC, and CHI had the highest chitin contents, followed by L. Consumption of CR or L significantly reduced fat mass, improved glucose sensi-tivity, and lowered hepatic cholesterol and triglycerides compared with E. CHI enhanced hepatic fatty acid β-oxidation. Gut microbiota analysis showed comparable α-diversity after CR, AC, L, and B diets, while high-fat sources (CHI, P, E) reduced diversity. CR increased Faecalibacterium prausnitzii, associated with antioxidant activity, whereas L promoted Bifidobacterium bifidum, inversely related to liver lipids. Both CR and L reduced circulating LPS and glucose AUC. Conclusions: These findings suggest that CR and L represent sustainable and health-promoting protein sources.