Iron and Zinc Biofortified Foods, Gut Microbiota in Gallus

Clinical Overview

This systematic review synthesizes five in vivo studies in Gallus gallus examining iron- and zinc-biofortified beans and wheat as dietary sources of Fe and Zn and their impact on intestinal microbiota and gut morphology. Across doses delivering approximately 26.9–48.7 µg Fe/g diet and 46.5 µg Zn/g diet, biofortified foods consistently increased short-chain fatty acid (SCFA)–associated taxa (including Lactobacillus, Bifidobacterium, Ruminococcus, Faecalibacterium) and reduced potentially pathogenic genera such as Escherichia, Enterobacter and Streptococcus, while improving villus architecture and goblet cell indices in several trials.

What was reviewed and who was studied

The review included five experimental studies conducted in the United States using Cornish Cross broiler chickens or chicken embryos (Gallus gallus) as models of human gut physiology and mineral absorption. All studies compared Fe- or Zn-biofortified beans (Phaseolus vulgaris L.) or wheat (Triticum aestivum L.) to their conventional counterparts, using either intra-amniotic soluble extracts (50 mg/mL) or post-hatch diets in which biofortified material comprised roughly 34.6–80% of the feed, over up to 6 weeks of feeding, with gut microbiota profiled primarily by 16S rRNA gene sequencing or targeted 16S rDNA PCR.

Major findings

The included studies collectively demonstrate that Fe and Zn biofortified staple crops can remodel the intestinal microbial community toward SCFA-producing and phenolic-metabolizing taxa, while limiting specific pathobionts, without evidence of dysbiosis or adverse microbial shifts at the tested doses.

Aspect	Finding
Biofortified matrices and mineral levels	Fe-biofortified carioca beans at 34.6–42% of diet provided 47.0–48.7 µg Fe/g vs 33.7–40.5 µg Fe/g in controls; Fe-biofortified wheat at 80% of diet provided 28.9 vs 25.9 µg Fe/g; Zn-biofortified wheat at 75% of diet provided 46.5 vs 32.8 µg Zn/g. Speciation was largely food-matrix bound Fe or Zn, with additional comparisons to Fe-EDTA and Fe–nicotianamine in one study.
Community-level changes	Three studies using 16S rRNA sequencing reported significant differences in β-diversity between biofortified and control diets; α-diversity effects were mixed, with some studies reporting no changes and one reporting increased diversity with Fe-biofortified wheat.
Phylum-level shifts	Zn-biofortified wheat increased Bacteroidetes and maintained Firmicutes and Proteobacteria; Fe-biofortified beans increased Firmicutes in some studies; Fe-biofortified wheat increased Actinobacteria while reducing Firmicutes and Proteobacteria.
SCFA-associated genera	Biofortified diets increased lactic acid bacteria (including Lactobacillus reuteri) and butyrate-associated taxa such as Ruminococcus, Coprococcus, Lachnospiraceae, and other SCFA-producing Firmicutes; acetic, propionic and valeric acid production increased in several trials.
Phenolic-catabolizing bacteria	Fe-biofortified beans enriched Eggerthella lenta, Faecalibacterium prausnitzii, Barnesiella spp., and other Coriobacteriaceae and Dehalobacteriaceae members linked to phenolic catabolism, consistent with higher phenolic content in biofortified beans.
Reduction of potential pathogens	Fe-biofortified wheat reduced Proteobacteria and Escherichia and Streptococcus genera up to 2-fold; intra-amniotic Fe-biofortified bean extracts lowered Escherichia coli in some bean types. Enterobacter was also reduced in biofortified wheat–fed birds.
Gut morphology and barrier features	Zn- and Fe-biofortified diets increased goblet cell density or number in some studies, and Fe-biofortified beans increased villus height and diameter, suggesting improved mucosal barrier and absorptive surface.
Microbial functional prediction	One Fe-biofortified bean study reported depletion of bacterial transcription and mineral absorption pathways (KEGG) in biofortified versus control diets, interpreted as luminal Fe being less utilized by bacteria and more available to the host.

Implications for Microbial Metallomics

The reviewed work links Fe and Zn enrichment in staple crops to shifts in the gut metallome–microbiome interface, favoring SCFA-producing and phenolic-metabolizing taxa while constraining specific Proteobacteria and streptococcal lineages in Gallus gallus.

Concept	Implication
Increased Fe and Zn in staple crops	Biofortification at roughly 50% of diet alters microbial ecology without promoting overgrowth of Fe- or Zn-dependent pathogens, suggesting that mineral-enriched plant matrices can support host mineral status and intestinal homeostasis simultaneously.
Enrichment of SCFA-producing Firmicutes	Expansion of Lactobacillus, Ruminococcus, Lachnospiraceae and related taxa implies that Fe/Zn-enriched diets can indirectly enhance SCFA-driven epithelial energy supply, mucus production, and mineral absorption efficiency.
Expansion of phenolic-catabolizing Actinobacteria and Coriobacteriaceae	Fe-biofortified beans appear to co-deliver phenolics that select for Eggerthella and Faecalibacterium, suggesting a coupled metal–phytochemical modulation of microbial metabolism relevant to redox and barrier regulation.
Reduction of Proteobacteria and Escherichia	Lower Proteobacteria and Escherichia with Fe-biofortified wheat argue that plant-based iron enrichment can differ fundamentally from pharmacologic iron supplementation, potentially avoiding pro-inflammatory dysbiosis.
Goblet cell and villus adaptations	Increased goblet cell density and villus dimensions under biofortified diets suggest that metallome shifts translate into structural remodeling of the mucosa, with downstream consequences for microbial niches and mineral flux.
Inferred reduction in bacterial Fe utilization	Depletion of bacterial mineral-absorption pathways in Fe-biofortified bean diets hints that binding of Fe within plant matrices and concurrent SCFA production may channel Fe toward host transporters rather than bacterial sequestration.

Limitations

The review is based on only five in vivo studies, all using Gallus gallus, limiting generalizability to humans and other animal models. Random sequence generation, outcome randomization, and blinding were frequently unclear in risk-of-bias assessment. Microbial outcomes relied mainly on 16S rRNA profiling without direct metagenomic or metabolomic characterization, and SCFA measures and clinical phenotypes were not consistently reported across studies.

Future perspectives

Next-step work should extend these Fe- and Zn-biofortified bean and wheat interventions into other mammalian models and human cohorts, with harmonized doses approximating 50% dietary contribution, to validate microbiota and SCFA changes. Parallel metagenomic, metatranscriptomic, and targeted metabolomic analyses could more precisely map metal-responsive pathways, phenolic metabolism, and SCFA production. Studies should explicitly quantify luminal and mucosal Fe and Zn speciation, including chelation states such as nicotianamine-bound Fe, and relate these to bacterial metal transporters, host brush-border metal transport gene expression, and intestinal histomorphometry under controlled, blinded experimental designs.

Key takeaways for Researchers and Clinicians

This systematic review evaluates Fe- and Zn-biofortified common beans and wheat in Gallus gallus models, at dietary levels delivering approximately 27–49 µg Fe/g and 47 µg Zn/g feed. The key metals are iron and zinc in plant-bound and chelated forms (including Fe–nicotianamine and Fe–EDTA), with no explicit oxidation state reported. Biofortified diets consistently associate with increased SCFA-related Firmicutes and Actinobacteria and decreased Proteobacteria, Escherichia, Streptococcus and Enterobacter, with several studies reporting fold-changes in the 1.2–2.0 range for specific genera.

Methodologically, the work demonstrates that Gallus gallus, coupled with 16S rRNA sequencing and intra-amniotic or dietary exposure designs, can sensitively detect microbiome responses to modest changes in plant-borne Fe and Zn content. Clinically, these data suggest that Fe/Zn biofortification of staple foods may avoid the dysbiotic patterns reported with some conventional iron fortification, instead supporting SCFA-producing, phenolic-metabolizing communities and healthier mucosal architecture. The translational hook for microbial metallomics is that manipulating the metal content and speciation of staple crops appears to offer a dual lever on host mineral status and gut microbial ecology, potentially informing future diagnostic and dietary interventions for iron and zinc deficiency.

Citation

Juste Contin Gomes M, Stampini Duarte Martino H, Tako E. Effects of Iron and Zinc Biofortified Foods on Gut Microbiota In Vivo (Gallus gallus): A Systematic Review. Nutrients. 2021;13(1):189. doi:10.3390/nu13010189