How Precision Diets, Through Gut Bacteria, Affect Anemia in Nepalese Adolescent

1. INTRODUCTION Anemia represents one of the most significant global public health challenges, affecting an estimated 1.74 billion people worldwide, with disproportionately higher prevalence among adolescent girls and women of reproductive age.Adolescence constitutes a critical developmental window characterized by rapid growth velocity, increased iron requirements, and heightened physiological susceptibility, particularly among females due to the onset of menstruation. Iron deficiency anemia (IDA) during this developmental period has been associated with impaired cognitive function, reduced physical work capacity, compromised immune competence, and adverse reproductive health outcomes in later life .

While iron deficiency remains the predominant etiological factor for anemia globally, emerging evidence demonstrates that anemia represents a complex, multifaceted disorder influenced by nutritional quality, inflammatory status, infectious disease burden, and biological variables including gut microbiota composition.The gut microbiome has emerged as a critical regulator of systemic iron homeostasis through multiple mechanistic pathways: (1) direct competition with the host for luminal iron; (2) modulation of intestinal inflammation and barrier function; (3) production of short-chain fatty acids (SCFAs), particularly butyrate, which influence hepcidin expression and iron absorption; and (4) immune-mediated regulation of iron absorption.

We hypothesize that dietary patterns, particularly vegetarian diets prevalent in South Asian populations, alter gut microbiota composition toward phyla producing higher levels of butyrate and propionate, which may down-regulate hepcidin expression and enhance intestinal iron absorption. Conversely, dysbiosis of microbiota profiles characterized by pathogenic overgrowth may promote intestinal inflammation, up-regulate hepcidin, and impair iron bioavailability despite adequate dietary intake.

South Asia bears one of the highest burdens of adolescent anemia globally, with over 50% of adolescent girls affected according to UNICEF and WHO estimates . This elevated prevalence results from the convergence of multiple risk factors: monotonous cereal-based diets with low bioavailable iron content, gender-based nutritional inequities, inadequate sanitation infrastructure, high prevalence of soil-transmitted helminth infections, and limited dietary diversity. Although Weekly Iron-Folic Acid Supplementation (WIFAS) programs have been implemented throughout the region, their efficacy in reducing anemia prevalence has demonstrated limited success, suggesting that traditional supplementation approaches may be insufficient to address the biological complexity and underlying determinants of anemia in this population.

Recent advances in nutritional science have highlighted the bidirectional relationship between iron supplementation and gut microbiota composition. Oral iron supplementation has been demonstrated to alter intestinal microbial ecology, potentially promoting pathogenic bacterial proliferation and intestinal inflammation, which may paradoxically impair iron absorption and increase gastrointestinal side effects. These findings underscore the critical importance of understanding diet-microbiome interactions when developing contextually appropriate anemia interventions.

Nepal exemplifies the challenges of addressing adolescent anemia in resource-limited settings. According to the Nepal Demographic and Health Survey (NDHS) 2022, anemia affects 39.4% of adolescent females aged 15-19 years, with higher prevalence observed among individuals from lower socioeconomic strata and specific ecological regions.Despite sustained national nutrition programs emphasizing iron supplementation and dietary diversity promotion, anemia prevalence has demonstrated only modest decline over the past decade16. Iron deficiency and inflammation are further exacerbated by recurrent gastrointestinal infections, poor sanitation, and high dietary-phytate content from plant-based staples, which inhibit non-heme iron absorption17,18.

Research on the molecular mechanisms underlying anemia in Nepal remains substantially under-explored, particularly regarding the relationship between dietary patterns, gut microbiota composition, and iron metabolism in adolescent populations. Existing studies have primarily focused on prevalence quantification, dietary intake assessment, and program evaluation, leaving critical knowledge gaps regarding the biological pathways connecting nutrition, microbiome function, and anemia status . Closing this evidence gap is essential for developing precision nutrition interventions that are context-specific, physiologically informed, and demonstrably more effective than conventional blanket supplementation approaches. 2. STATEMENT OF THE PROBLEM Despite the extensive implementation of iron-folic acid supplementation programs and school-based nutrition initiatives, anemia among adolescent girls remains highly prevalent in Nepal, representing a persistent public health priority .Previous research on anemia in Nepal has predominantly employed a population-level epidemiological approach, focusing on prevalence quantification, identification of dietary and socioeconomic risk factors, and assessment of supplementation program compliance. While these studies provide valuable public health insights, they fail to account for inter-individual biological variation in anemia etiology and response to interventions.

A critical gap in Nepalese anemia research is the paucity of studies examining the role of gut microbiota in iron absorption and anemia outcomes. International evidence demonstrates that gut microbiota composition significantly influences iron bioavailability, inflammatory pathways, and host response to iron interventions .However, no studies in Nepal have examined how gut microbial profiles interact with dietary patterns to influence anemia status in adolescent girls. Given the high prevalence of enteric infections, subclinical inflammation, dietary iron absorption inhibitors, and soil-transmitted helminth infections in Nepal, this represents a substantial knowledge gap with direct implications for intervention design.Furthermore, Nepal's ongoing nutritional transition, characterized by the coexistence of traditional diets with increasing processed food consumption, may be altering gut microbiota composition and nutritional status in ways that affect anemia risk22. The interaction between helminth infections, gut microbiota, and iron status remains particularly understudied, despite evidence that hookworm and Ascaris infections profoundly affect both intestinal microbial ecology and host iron metabolism.

The continued application of generalized, non-targeted interventions without mechanistic understanding risks perpetuating suboptimal outcomes and inefficient allocation of limited public health resources. Therefore, there is an urgent need for mechanism-based, precision nutrition approaches to address anemia in Nepalese adolescent girls. This research aims to generate novel, context-specific evidence that can guide more targeted and effective anemia interventions by investigating the relationships between dietary patterns, gut microbiota composition, and anemia status. 3. OBJECTIVES 3.1 General Objective To determine the prevalence and determinants of anemia in adolescent girls and to study the diet-microbiome interactions in the sub-sample to provide precision nutrition interventions in Kathmandu, Nepal.

3.2 Specific Objectives

1. To determine the prevalence and typology of anemia among adolescent girls in selected schools of the Kathmandu through comprehensive hematological assessment. 2. To distinguish gut microbiota among anemic and non-anemic adolescent girls. 3. To evaluate the efficacy of goat liver supplementation over traditional supplementation in improving anemia-related biomarkers over a 12-week period. 4. To assess changes in gut microbiota composition following interventions and identify microbial species associated with improved anemia outcomes.

4\. RESEARCH QUESTIONS

1\. What is the prevalence and distribution of anemia types (iron deficiency and megaloblastic) among adolescent girls in the Kathmandu? 2. How does gut microbiota differ in anemic and non-anemic adolescent girls? 2. Does gut microbiota composition change following precision intervention, and are specific microbial taxa associated with treatment response? 3. What is the effectiveness of nutrition interventions, including animal-source food supplementation, among adolescent girls? 5. SIGNIFICANCE OF THE STUDY This research addresses a critical health priority for Nepal and directly contributes to Sustainable Development Goal 3 (Good Health and Well-being). By generating empirical evidence on diet-microbiota-anemia relationships, this study will fill a significant knowledge gap with direct policy relevance for national nutrition programs.

Understanding how dietary patterns, particularly vegetarian diets, interact with gut microbiota to influence anemia status can inform the development of contextually appropriate nutrition education and dietary guidelines. The evaluation of goat liver as a culturally acceptable, food-based intervention represents a novel approach that could identify sustainable strategies to complement existing supplementation programs. Goat liver is particularly suitable for the Nepalese context due to its high bioavailable iron content (approximately 3.3 mg per 100g), abundant vitamin B12, widespread availability, and relatively low cost compared to other animal-source foods.

This study will be among the first in South Asia to integrate microbiome analysis with nutritional and hematological assessments in an adolescent population, contributing valuable evidence on the feasibility and potential benefits of food based supplement approach in resource-limited settings. The findings will have direct applicability to national adolescent health policy, school feeding programs, and anemia control strategies in Nepal and similar contexts throughout the region.

Furthermore, this research will build local capacity in microbiome and nutrition epidemiology research through collaboration with Nepali institutions, contributing to the development of sustainable research infrastructure for addressing priority public health questions.

6\. METHODOLOGY 6.1 Research Design This study employs a mixed-methods design consisting of two sequential phases that integrate quantitative epidemiological assessment with experimental intervention methodology. The design progression moves from descriptive cross-sectional analysis to randomized controlled intervention, enabling both prevalence characterization and causal inference regarding precision nutrition interventions.

Phase 1: Cross-sectional survey Phase 2: Randomized controlled trial (RCT) of precision interventions Phase 1: Cross-Sectional Survey (Baseline Assessment)

Design Characteristics:

Type: Descriptive, observational cross-sectional study Purpose: Establish anemia prevalence, typology distribution, and baseline population characteristics Duration: 3-4 months for data collection and preliminary analysis Analytical Approach: In Phase 1, descriptive statistics will be employed to estimate the prevalence of anemia and its typology within the study population. Following this, exploratory factor analysis will be conducted to identify distinct dietary patterns from the food frequency questionnaire data. Additionally, logistic regression analysis will be performed to assess the association between potential risk factors and anemia status, thereby identifying key determinants of anemia among adolescent girls in the Kathmandu Valley.

Primary Functions of Phase 1:

Prevalence Quantification: Generate representative estimates of anemia types (iron deficiency, megaloblastic, mixed) among adolescent girls

• Serum ferritin levels [Time frame: 12 weeks]
• Serum transferrin receptor (sTfR) [Time frame: 12 weeks]
• Serum folate concentration [Time frame: 12 weeks]
• Gut microbiota composition [Time frame: 12 weeks]
• Improved Diet [Time frame: 12 weeks]
• Vitamin B12 Status [Time frame: 12 weeks]