Gut bacteria and brain aging compared between African and Western populations

Recent studies reveal both shared and disease-specific gut microbial alterations across Parkinson’s disease (PD) and Alzheimer’s disease (AD), suggesting common pathways that may be influenced by microbiota-based interventions (Table 1). Verrucomicrobia consistently emerges as a recurrent signature, with increased abundance reported in PD and AD (Heravi et al., 2023; Koutsokostas et al., 2024; Nishiwaki et al., 2022; Rob et al., 2025). This increase is primarily driven by its genus, Akkermansia, which has been linked to gut barrier modulation and pro-inflammatory signaling, lipopolysaccharide (LPS) production and modulation of immune signaling pathways, including upregulation of CASP1, TRAF5, and STAT5B (Derrien et al., 2011; Zhang and Wang, 2023) While Akkermansia is generally recognized for its beneficial effects on gut health and barrier modulation in non-disease states (Chiantera et al., 2024; Gao et al., 2025), its sustained elevation specifically in neurodegenerative contexts has been associated with barrier dysfunction, systemic inflammation, and reduced levels of metabolites, suggesting a shift in its functional implications during disease progression (Jian et al., 2023).

Firmicutes, encompassing key SCFA producers such as Faecalibacteriaceae and Lachnospiraceae, have been consistently reduced across several studies on brain aging (Koutsokostas et al., 2024; Sun et al., 2019). In contrast, Proteobacteria and Actinobacteria were elevated, reflecting a pro-inflammatory microbial environment (Koutsokostas et al., 2024). At the genus level, reported increases in Methanobrevibacter and Megasphaera in PD suggest alterations in methane production and lactate metabolism, potentially affecting gut motility and immune regulation (Cabral and Weimer, 2024; Ghoshal et al., 2016). Similarly, multiple studies have reported higher levels of Collinsella and Subdoligranulum in PD (Zeng et al., 2024) and AD (Borrego-Ruiz and Borrego, 2025; Rob et al., 2025), linking these taxa to oxidative stress, dopaminergic neuron damage, and anxiety-related phenotypes (Dias et al., 2013; Mendez, 2021). Comparative analysis reveals a mix of overlapping and distinct microbial patterns across the different NDs. PD and AD share alterations in Lactobacillus (Chui et al., 2024), Collinsella (Rob et al., 2025), Prevotella (Chui et al., 2024), and Akkermansia (Heravi et al., 2023), pointing to overlapping mechanisms involving neuroinflammation, protein misfolding, and neurotransmitter dysregulation. Conversely, emerging literature reported a decrease in Blautia abundance in PD, therefore, presenting a significant limitation for drawing overarching conclusions. These microbial shifts reflect disrupted gut-brain communication characterized by systemic and CNS inflammation, impaired blood-brain barrier integrity, and altered metabolite production.

Collectively, many of these ND-associated microbial signatures mirror those observed in healthy aging populations, including reduced Firmicutes, enrichment of Proteobacteria and Verrucomicrobia, and loss of SCFA-producing taxa (Koutsokostas et al., 2024). These shared alterations suggest that age-related dysbiosis may lay the foundation for neuropathological changes, with disease states representing more advanced conditions.

Gut microbiota-derived metabolites have been associated with neuronal function, influencing neuroinflammation, neurotransmission, and disease pathophysiology (Rob et al., 2025; Table 2).

Communities are categorized based on their degree of urbanization, dietary patterns and living habit (de Lanerolle-Dias et al., 2015; Zhao et al., 2023). For instance, rural communities are generally small cities compared to urban habitats with a more complex network. In terms of dietary habits, urban populations tend to eat more ultra-processed foods than those living in rural areas, who generally consume traditional staple grains and minimally processed plant-based foods (Li and Lu, 2021). Several cross-sectional studies have characterized the gut microbiota of rural African populations consuming traditional diets rich in unprocessed plant foods, resistant starches, and fibers. Across different countries, including South Africa, Malawi, Tanzania, Cameroon, Liberia, Zimbabwe, Burkina Faso, Nigeria, and Uganda, rural communities exhibit microbial profiles dominated by Prevotella, Bifidobacterium, Faecalibacterium, Ruminococcus, and other fiber-degrading taxa (Allali et al., 2018; Ayeni et al., 2018; De Filippo et al., 2010; Lokmer et al., 2020; Morton et al., 2015; Oduaran et al., 2020; Ordiz et al., 2015, 2020; Osakunor et al., 2020; Rosa et al., 2018; Rubel et al., 2020; Schnorr et al., 2014). These taxa are often accompanied by a higher prevalence of Lachnospiraceae and Ruminococcaceae, reflecting the fermentation of complex polysaccharides (Flint et al., 2012). Many of these communities exhibit greater overall microbial richness and diversity compared to urban or Western populations, with a taxonomic structure adapted to fiber fermentation and SCFA production (de la Cuesta-Zuluaga et al., 2018). These taxa may also be associated with frequent contact with the natural environment, such as soil and vegetation, which is postulated to enrich the gut microbiota composition (Frame et al., 2019). High interaction with the natural environment has remained a major characteristic of rural communities, giving rise to the term “rural microbiome” (Du et al., 2021). Various research demonstrates that the rural microbiome can enhance health and protect against chronic illnesses (Blaser, 2017; Zuo et al., 2018). In contrast, studies conducted in urban African settings have revealed more variable gut microbiota compositions, often characterized by a relative increase in Clostridium and Bacteroides taxa, along with a decline in the Prevotella genus (Ayeni et al., 2018; Rocafort et al., 2019; Samb-Ba et al., 2014; Smith et al., 2013). African cohorts with nutrient-deficient, metabolic, or infectious conditions (Allali et al., 2018; Doumatey et al., 2020; Fassatoui et al., 2019; Lokmer et al., 2020; Oduaran et al., 2020; Ordiz et al., 2015, 2020; Osakunor et al., 2020; Parbie et al., 2021; Rubel et al., 2020; Salah et al., 2019; Smith et al., 2013; Tang et al., 2017) also reported a decline in Prevotella taxa, indicating that urbanization, westernized diets, and disease burden may contribute to a microbiota transition toward less fiber-fermenting and more proteolytic bacterial taxa. This shift aligns with a pattern of reduced microbial diversity and potential pro-inflammatory signatures, commonly associated with metabolic disorders and compromised gut integrity (Severino et al., 2024). These findings highlight the emerging differences between the traditional, Prevotella-enriched “rural microbiome” and the increasingly heterogeneous, Clostridium/Bacteroides-dominated “urban microbiome,” shaped by modernization and changing nutritional environments. Therefore, longitudinal studies of cognitive function in rural African cohorts, in relation to microbiota profiles to quantify neuroprotective performance associated with their traditional diets, are necessary.

Urbanization is associated with rapid dietary and lifestyle shifts, including increased consumption of refined carbohydrates, animal products, and processed foods (Casari et al., 2022). Comparative studies within Africa reveal clear microbial stratification between rural and urban populations. Rural residents typically maintain high Prevotella-to-Bacteroides ratios and harbor fiber-adapted communities. In contrast, urban populations show declining Prevotella abundance and a gradual shift toward microbiota configurations resembling Western profiles. Urban cohorts often present reduced diversity, lower abundance of SCFA producers, and increased representation of opportunistic or potentially inflammatory species of Bacteroides and Enterobacteriaceae (Abjani et al., 2023; Ecklu-Mensah et al., 2023; Huang et al., 2023). These trends mirror the ongoing nutrition transition and may reflect the impact of reduced dietary fiber and increased fat and sugar intake on microbial ecology.

Western populations have reported microbial communities that are less diverse and skewed toward taxa adapted to simple carbohydrates and animal-based substrates (Beam et al., 2021; Clemente-Suárez et al., 2023a; Makki et al., 2018). These microbiota profiles are characterized by higher Bacteroides prevalence, lower Prevotella, and reduced SCFA production capacity. Several studies have also shown a decrease in mucin-degrading capacity and thinning of the intestinal mucus layer, resulting in increased gut permeability and inflammation in Western populations (Desai et al., 2016; Makki et al., 2018; Suriano et al., 2022). Comparative analyses between African rural communities and Western cohorts consistently show marked differences in microbial structure and function, with African groups exhibiting higher levels of saccharolytic fermentation and enriched pathways for the degradation of complex carbohydrates (Brewster et al., 2019; De Filippo et al., 2010). These differences highlight observed disparities in inflammatory profiles and may contribute to differential trajectories of brain aging across populations (Shi et al., 2021; Zhang F. et al., 2022). In a comparative study using Malawian and Finnish children fed the same diets, but under different environmental conditions, significant changes in the microbiome and specific taxa distribution were observed. Bifidobacteria were dominant in all infants, with a greater proportion in Malawian (70.8%) than in Finnish infants (46.8%). Additional distinctions among bacterial genera were observed, with species like Bifidobacterium adolescentis, Clostridium perfringens, and Staphylococcus aureus being absent in Malawian but detected in Finnish infants (Grześkowiak et al., 2012). These differences suggest that African microbiota profiles may have greater protection against neuroinflammation through sustained SCFA production and mucosal integrity, but rapid urbanization threatens these benefits. In contrast, the Westernized gut microbiota, marked by lower microbial diversity (D’Aloisio et al., 2025) and reduced SCFA-producing taxa (Agus et al., 2016), reflects dietary shifts toward refined carbohydrates and animal-based fats. This profile is associated with heightened intestinal permeability (Severino et al., 2024), systemic inflammation (Christ et al., 2019), and decreased neuroprotective signaling (Kanoski and Davidson, 2011), all of which are risk factors for accelerated cognitive decline and neurodegenerative disease (Noble et al., 2017; Solch-Ottaiano et al., 2023).

It is a common oversimplification to refer to a single “African diet.” The continent is home to immense ecological and cultural diversity, resulting in a wide array of dietary patterns. However, many traditional, rural African diets share core characteristics that distinguish them from the typical Western diet, which is high in fat, sugar, and low in fiber (Statovci et al., 2017). Predominantly, these diets are plant-based and exceptionally rich in dietary fiber, derived from a variety of sources, including whole grains, legumes, tubers, fruits, and vegetables, all of which are rich in resistant starches and complex carbohydrates crucial for gut microbial diversity and function (Aworh, 2023). Those found in staples vary by region, but may include minimally processed cereals such as sorghum, millet, and teff, and starchy tubers like cassava and yams (Ghosh et al., 2023). Complex carbohydrates or resistant starches are high in these staples and cannot be digested in the upper portion of the gastrointestinal tract but are fermented in the colon. In rural South Africa, for example, many diets focus on maize meal porridge and legumes, and fiber consumption regularly exceeds 50 g per day, almost 3 times the daily intake in most Western nations, which typically range from 15 to 20 g per day (O’Keefe et al., 2015; Papier et al., 2025; Quagliani and Felt-Gunderson, 2017). In Burkina Faso, traditional diets consist of large amounts of sorghum, millet, and vegetables, hence, an abundance of fiber-degrading bacteria in their gut microbiome (De Filippo et al., 2010).

A typical characteristic of most traditional African food practices is heavy reliance on the fermentation process as a means of food preparation and preservation. This practice extends the shelf-life of foods and also introduces live microorganisms (probiotics) and their beneficial metabolites (postbiotics) (Marco et al., 2021). Natural fermented foods (for example, fufu, a fermented cassava meal in West African countries; ogi, a sour maize porridge in Nigeria; injera, a sourdough flatbread in Ethiopia made with teff; and mahewu, a non- alcoholic fermented maize beverage in Southern Africa) are part of the daily diet (Siddiqui et al., 2023). These foods are known sources of SCFA-producing bacteria, such as Lactobacillus and Bifidobacterium species (Malongane and Berejena, 2024; Mgbodile and Nwagu, 2023). This habitual use of fermented foods contrasts with the Western diet, where fermented products are less prevalent and the intake of microbes is restricted by sterilization and food processing.

The distinct composition of traditional African diets directly fosters a unique gut microbial ecosystem. The high availability of diverse, non-digestible carbohydrates is the primary driver behind the enrichment of specific bacterial taxa that are less abundant in populations consuming a Western diet. The most widely reported marker of a high-fiber diet of non-Western origin is a high proportion of the genus Prevotella (Gorvitovskaia et al., 2016). In addition to Prevotella, fiber-rich diets promote the growth of butyrate-producing bacteria, which are important for gut and systemic health. Abundances of Faecalibacterium, Roseburia, and Ruminococcus have been reported to be potent fermenters of resistant starch and dietary fiber, resulting in the formation of short-chain fatty acids (SCFAs), specifically butyrate (Koh et al., 2016). Butyrate is the primary energy source for colonocytes, thereby enhancing the integrity of the gut barrier. Additionally, traditional Africans’ diets are low in processed foods and artificial sweeteners, and high in saturated fats (Oniang’o et al., 2025). This usual intake is hypothesized to promote overall health by supporting the diversity of the gut microbiota (De Filippo et al., 2010), enhancing immune response (Temba et al., 2025), and influencing hormone secretion through microbial metabolites (Samami et al., 2025).

Although some of the most effective correlational studies are based on cross-sectional research in African populations, dietary intervention studies, usually conducted in Western cohorts, provide causal evidence of the rapid and drastic effect of diet on the microbiome (Wilson et al., 2020). One of the most compelling pieces of evidence comes from the dietary swap study by O’Keefe et al. (2015). In this pioneering research, rural Africans were placed on a low-fiber, high-fat Western diet, while African Americans consumed a high-fiber, low-fat traditional African diet. Participants who switched to the African-style diet showed a marked increase in saccharolytic fermentation and butyrate production, accompanied by reductions in colonic mucosal markers of inflammation and proliferation, both of which are considered biomarkers of colorectal cancer risk. In contrast, those on the Western-style diet exhibited changes associated with a higher risk of disease. Furthermore, treatments that administer certain types of fiber have also reported measurable shifts in the bowel microbiome. Supplementation with inulin-type fructans, galactooligosaccharides (GOS), and inulin has been shown to specifically increase the abundance of Bifidobacterium species (Carlson et al., 2018). This evidence suggests that a diet dominated by complex plant polysaccharides is a consistent choice that can support a healthy and metabolically resilient microbiome. The eating habits of traditional rural African societies, marked by increased consumption of fiber and fermented foods, are essential for maintaining a healthy gut, thereby promoting healthy brain aging.

Longitudinal studies linking gut microbiota profiles to brain aging and neurodegenerative disease outcomes in African populations are limited. However, epidemiological and nutritional evidence support the biological mechanisms discussed in this review. According to the Institute of Health Metrics and Evaluation (IHME), African regions have an Alzheimer’s disease and other dementia prevalence of 0.2% as of 2021, while South America, North America, Europe, and Eastern Asia and Pacific had a reported prevalence of 0.7%, 1.5%, 1.6%, and 1.1%, respectively (IHME and Global Burden of Disease, 2024). Limited surveillance infrastructure in Africa has contributed to uncertainty in these estimates. However, recent studies indicate a rapid rise in age-related neurodegenerative disorders as populations age and urbanization accelerates across the continent (Olajide et al., 2025).

This emerging epidemiological transition coexists with heightened dietary shifts. Traditional African diets are increasingly being replaced in urban and peri-urban settings by Westernized dietary patterns (Ameye et al., 2025). These dietary changes align with alterations in gut microbiota composition observed in urban African populations (Figure 2). Additionally, the microbial composition enriched in traditional rural African diets aligns closely with mechanisms that support brain health (Isibor et al., 2021). High SCFA production, enhanced gut barrier integrity, and reduced systemic inflammation have been associated with neurogenesis, reduced microglial activation, improved mitochondrial health, and attenuation of neuroinflammatory signaling (Jabbari Shiadeh et al., 2025). In contrast, microbiota alterations associated with Westernized diets are consistently linked to increased gut permeability, chronic low-grade inflammation, and impaired neuroprotective signaling pathways. All of which are recognized contributors to accelerated brain aging and neurodegeneration (Wiêckowska-Gacek et al., 2021). These population-level and mechanistic observations support a biological framework that the traditional African diet may influence brain aging through microbiota-mediated pathways.