Extruded blue corn and tepary beans-based tortillas’ impact on obesity and gut microbiota in vivo

Technical Summary: Extruded Blue Corn and Tepary Beans-Based Tortillas' Impact on Obesity and Gut Microbiota In Vivo

Problem Statement
Obesity is a complex chronic disease influenced by macroscopic, biochemical, and gut microbiota factors. While tortillas are a staple food in Mexico and Latin America, representing up to 20% of daily caloric intake, their specific impact on obesity parameters remains controversial. Epidemiological data presents conflicting views: some studies suggest rural dietary patterns including tortillas are not associated with excess weight, while others indicate a direct correlation between high tortilla consumption and obesity. Furthermore, traditional nixtamalized corn tortillas often lack sufficient lysine, tryptophan, and certain vitamins. There is a need to evaluate whether technological modifications, such as extrusion and the fortification with nutrient-dense legumes like tepary beans (Phaseolus acutifolius), can enhance the nutritional profile of tortillas and mitigate obesity-associated metabolic dysregulation and gut microbiota alterations.

Methodology
The study employed an in vivo model using 48 male Wistar rats (n=8 per group) over an 18-week period. The animals were divided into five groups:

1. Standard Diet (SD): Control group.
2. High-Fat and High-Fructose Diet (HFFD): Obese control group.
3. HFFD + Nixtamalized White Corn (NWC): HFFD supplemented with traditional tortillas.
4. HFFD + Extruded Blue Corn (EBC): HFFD supplemented with extruded blue corn tortillas.
5. HFFD + Extruded Blue Corn and Tepary Beans (EBCB): HFFD supplemented with tortillas made from a 70:30 mixture of extruded blue corn and tepary beans.

The tortillas were manufactured using a single-screw extruder. The EBCB formulation utilized a 70:30 ratio of corn to beans, reflecting rural Mexican consumption patterns. The study assessed:

• Tortilla Composition: Proximate analysis (protein, lipids, starch, fiber) and characterization of polyphenols (total phenolic compounds, flavonoids, anthocyanins, and specific phenolic acids via UHPLC-DAD-ESI-QqQ MS/MS).
• Macroscopic and Biochemical Parameters: Body weight evolution, fasting glucose, insulin, HOMA-IR, total cholesterol, HDL, triglycerides, and caloric/fiber intake.
• Histopathology: Adipocyte area in subcutaneous adipose tissue.
• Gut Microbiota: 16S rRNA gene sequencing (V3-V4 regions) to analyze alpha and beta diversity, phyla abundance, and specific bacterial genera.
• Statistical Analysis: Data were analyzed using ANOVA, Kruskal-Wallis, Dunn's post-hoc tests, Principal Component Analysis (PCA), and Spearman's correlations.

Key Contributions and Results

• Nutritional and Phytochemical Profile: The EBCB tortillas demonstrated a 36–37% higher protein content compared to NWC and EBC tortillas. They contained lower lipid and digestible starch levels. While total phenolic content was similar across tortilla types, EBC and EBCB exhibited a greater diversity of phenolic compounds. Specifically, EBCB had the highest shikimic acid (41% higher than EBC) and quinic acid content. NWC retained the highest ferulic acid concentration, whereas EBCB was the only group to detect catechin.
• Metabolic and Body Weight Impact: The study found that tortilla consumption did not significantly alter body weight gain or fasting glucose levels among the HFFD groups. However, the EBCB group showed the lowest triglyceride levels among HFFD groups (though not statistically different from SD) and the lowest kilocalorie consumption. The EBC group exhibited the highest fiber consumption, exceeding even the standard diet group. No significant differences were observed in HOMA-IR or adipocyte area between the HFFD groups, suggesting that the tortilla supplementation did not exacerbate or significantly reverse insulin resistance or adipocyte hypertrophy induced by the HFFD.
• Gut Microbiota Modulation: The most significant findings related to gut microbiota diversity. The HFFD diet altered microbiota composition, characterized by increased Methanobacteriota and Actinomycetota and decreased Bacteroidota.
  • Diversity Restoration: The EBC and EBCB groups restored the Shannon index, Observed Species, and Chao1 values to levels similar to the Standard Diet group, whereas the NWC group failed to restore these diversity metrics.
  • Phyla and Genera: EBC and EBCB partially restored Bacteroidota levels to those of the SD group. The consumption of tortillas promoted bacterial genera linked to carbohydrate and polyphenol metabolism, including Ruminococcus, Allobaculum, Parasutterella, and Turicibacter. Notably, EBCB was the only group to partially restore a genus from the Gastranaerophilales order.
  • Correlations: PCA and correlation analyses indicated that phytochemicals such as extractable proanthocyanidins, total flavonoids, and specific acids (quinic, shikimic) were positively associated with increased bacterial diversity and the presence of beneficial genera.

Significance and Claims
The paper concludes that while the consumption of extruded blue corn and tepary bean-based tortillas (EBCB) did not significantly reduce body weight gain or fully reverse metabolic dyslipidemia in this specific in vivo model, it successfully modulated the gut microbiota. The EBCB formulation, rich in protein, fiber, and diverse polyphenols, restored gut microbial diversity (Shannon index, Observed Species) and promoted bacterial populations associated with the metabolism of fiber and polyphenols.

The authors assert that tortilla consumption, particularly when fortified with legumes and processed via extrusion, does not adversely affect dyslipidemia and offers a potential strategy to improve gut microbiota populations in the context of an obesogenic diet. The study highlights that the beneficial effects on the microbiome were not necessarily coupled with immediate macroscopic metabolic improvements in this specific timeframe and model, suggesting that the health benefits of these tortillas may be mediated through gut ecology rather than direct weight loss mechanisms. The research supports the potential of extruded, legume-fortified tortillas as a functional food that preserves or restores gut microbial balance without exacerbating obesity-related parameters.