Diet, Gut Microbiota, and Metabolic Syndrome Across the Urban-Rural Divide in Sub-Saharan Africa

Abstract

The prevalence of Metabolic Syndrome (MetS) continues to rise globally, driven by multiple factors including lifestyle, dietary changes, and genetic predispositions. Recently, the role of gut microbiota in metabolic health and disease has received increasing scientific attention because of its critical involvement in the regulation of metabolism, immunity, and energy balance. Alterations in the composition and diversity of the gut microbiota have been linked to several metabolic disorders including MetS. Compared to high income countries, the role of gut microbiota in the burden of MetS are relatively under-researched in many low-and-middle-income countries including sub-Saharan Africa. Therefore, this thesis compared dietary patterns, gut microbiota, and the burden of MetS and its components in parallel between two rural and urban districts in Tanzania. The thesis offers several key findings that complement existing evidence on the associations between diet, gut microbiota, and MetS and its components. Part 1 compares the dietary habits of the selected rural and urban districts of Tanzania and assesses its relationship with MetS and its components. In chapter 2 we show evidence that suggests the convergence of dietary patterns between rural and urban although dietary diversity, macronutrients, and energy intake are significantly higher in the urban population. Chapter 3 presents evidence for both dietary patterns and clusters. MetS/MetS components were found to be associated with MetS, dyslipidemia, and central obesity. Contrary to the hypothesis of this thesis and existing evidence, the prevalence of MetS and Hypertension was equally high in both rural and urban populations signifying shared risk factors between the two sites. In Part 2 - Chapter 4, a review of studies on urbanization, diet, and gut microbiota conducted between 2000 and 2022 in SSA, found gut microbiota diversity and richness to be consistently higher in rural and traditional communities compared to urban populations. These findings align with existing global evidence where rural dwellers - as seen in chapter 5 of this thesis - are more likely to adhere to plant-based diets rich in fiber associated with a higher exposure to environmental microbes which support a more diverse gut microbiota. However, across SSA no uniform distribution of specific taxa relative abundance/prevalence was observed along the urbanization gradient. In the same chapter, we examined the differences in the gut microbial functional capacity between the two sites and found contrasting relationships. Whereas the gut microbiota diversity was greater in rural samples the functional enrichment was lower and vice versa. In chapter 6, we assessed the relationship between gut microbiota and the disease outcomes – MetS and its components considering diet and other relevant lifestyle variables. Gut microbiota diversity, richness or functional capacity did not differ significantly based on disease status possibly showing greater effects are explained by geography and other covariates rather than diseases in this population.