Case Studies
Prebiotic Iron-fortified Cereal in Kenyan Infants: Randomized Control Trial
Clinical Overview
This randomized controlled trial in rural Kenyan infants (6–11 months, mostly anemic and iron deficient) tested wheat-based cereal containing 3.6 mg iron as ferrous fumarate with or without galacto-/fructo-oligosaccharide prebiotics. Prebiotics increased fractional iron absorption from 16.3% to 20.5% at baseline and up to 26.0% after 3 weeks, while lowering Enterobacteriaceae, fecal pH, and calprotectin, indicating improved gut microbiome profile and reduced intestinal inflammation.
Study Setting
The study was conducted in Kwale County, south Kenya, in a community setting. Infants aged 6–11 months without severe undernutrition, major illness, or recent antibiotics or iron supplements were enrolled; three-quarters were anemic and about 80% iron deficient at baseline in the absorption subset. Iron exposure was via twice-daily oral wheat-based instant cereal delivering 3.6 mg iron as ferrous fumarate plus ascorbic acid for 3 weeks, with randomized addition of either 7.5 g or 3 g short-chain GOS/long-chain FOS (9:1) or no prebiotic.
Study Design and Methods
| Aspect | Details |
|---|---|
| Design | Three-arm randomized controlled intervention (iron-only vs iron + 3 g GOS/FOS vs iron + 7.5 g GOS/FOS) with mechanistic iron stable-isotope substudy; 3-week follow-up. |
| Iron speciation & dosing | Cereal fortified with 3.6 mg iron as ferrous fumarate (FeFum) plus ascorbic acid at 4:1 molar ratio (ascorbic acid:iron), given twice daily. |
| Stable isotope metallomics | Subset received 57Fe- and 58Fe-enriched FeFum-labeled test meals (with and without prebiotic) before and after intervention; erythrocyte incorporation measured 14 days later by multi-collector ICP-MS to derive fractional iron absorption. |
| Microbiome characterization | Fecal samples analyzed by qPCR for total bacteria, Bifidobacterium spp., Lactobacillus/Pediococcus/Leuconostoc spp., Enterobacteriaceae and selected pathogens; 16S rRNA gene sequencing on all participants; shotgun metagenomics with toxin-gene prediction (PathoFact) on the isotope subset plus iron-only comparators. |
| Clinical / biochemical endpoints | Primary endpoint: fractional iron absorption from cereal meals with and without prebiotics, pre- and post-intervention. Secondary endpoints: fecal pH and calprotectin; plasma ferritin (with inflammation adjustment), soluble transferrin receptor, hepcidin, CRP, α1-acid glycoprotein; anthropometry. |
| Sample size | 191 infants randomized (61 iron-only, 60 iron + 3 g, 53 iron + 7.5 g completers); 66 infants in isotope absorption substudy (25 in 7.5 g and 28 in 3 g groups with complete FIA data). |
Major Findings
The trial links iron speciation (ferrous fumarate, 57Fe/58Fe labels) and prebiotic-conditioned gut ecology to markedly higher iron bioavailability and a less pro-inflammatory microbiome in iron-deficient Kenyan infants.
Across test meals, adding GOS/FOS acutely increased fractional iron absorption by 26% at baseline. After three weeks of daily prebiotic + iron cereal, FIA from a meal without prebiotic was 41% higher than the baseline iron-only meal, and FIA from a meal with prebiotic was 60% higher, indicating both acute and conditioning effects. In parallel, boxplots on page 8 show that the 7.5 g prebiotic arm had lower fecal pH and a ~20% reduction in calprotectin while the iron-only arm showed a modest increase, and qPCR plus sequencing data demonstrate higher Lactobacillus abundance and lower Enterobacteriaceae and summed pathogen genes in prebiotic recipients.
| Findings | Details |
|---|---|
| Acute prebiotic effect on iron absorption | Median FIA at baseline increased from 16.3% (8.0–27.6%) without prebiotic to 20.5% (10.4–33.4%) with prebiotic (Cohen’s d = 0.53; P < 0.001). |
| Conditioning effect after 3 weeks | FIA from a meal without prebiotic rose to 22.9% (8.5–32.4%), 41% higher than the baseline meal without prebiotic (P = 0.002). |
| Combined acute + conditioning effect | FIA from a meal with prebiotic after 3 weeks reached 26.0% (12.2–36.1%), 60% above the baseline iron-only meal (P = 0.007); no significant dose difference between 3 g and 7.5 g. |
| Gut microbiome shifts | Lactobacillus abundance increased in both prebiotic arms; Enterobacteriaceae and summed pathogens decreased in the 7.5 g arm versus iron-only; Bacteroides (3 g) and Prevotella (7.5 g) increased by 16S analysis. |
| Inflammation and microbial toxins | Fecal pH and calprotectin were lower in the 7.5 g group than iron-only; CRP was lower in the 3 g group; toxin-encoding genes, including a zinc-dependent phospholipase C, were reduced in the 3 g group by metagenomics. |
Mechanistic Interpretation & Microbial Metallomics
Above mentioned findings suggest that prebiotic modulation of gut ecology can simultaneously enhance iron bioavailability from ferrous fumarate and dampen iron-associated dysbiosis and inflammation.
| Concept | Implication |
|---|---|
| Acute prebiotic co-administration with FeFum | GOS/FOS in the same meal enhances FIA, plausibly via effects on iron solubility or luminal kinetics, allowing better utilization of low-dose iron. |
| Conditioning of gut by 3 weeks of prebiotics | Prior prebiotic exposure increases FIA even when the test meal lacks prebiotic, indicating durable metallomic changes in the absorptive environment. |
| Expansion of Lactobacillus spp. | Increased Lactobacillus in both prebiotic groups, alongside higher FIA, supports a role for lactic acid–producing commensals in promoting systemic iron uptake. |
| Reduction of Enterobacteriaceae and summed pathogens | Lower pathogen-associated Enterobacteriaceae and toxin gene abundance, especially with 7.5 g and 3 g prebiotics respectively, suggests that enhancing FIA need not come at the cost of pathogen overgrowth. |
| Lower fecal pH and calprotectin | Acidification and reduced gut inflammation in the 7.5 g arm indicate that prebiotic-conditioned microbiota can partially counter pro-inflammatory effects of luminal iron. |
| Stable microbiome trajectories | Lower Bray–Curtis dissimilarity to baseline in prebiotic arms suggests a more resilient microbial community despite ongoing iron exposure. |
Limitations
The intervention lasted only 3 weeks, limiting inference on longer-term iron status, growth, or clinical outcomes such as diarrhea. Fractional iron absorption was not measured in the iron-only group, so unmeasured factors might contribute to observed conditioning effects. Home-based cereal feeding and stool collection introduce adherence and sampling variability, and isotope substudy attrition reached ~18–20%.
Future perspectives
Future work should extend follow-up to several months to determine whether prebiotic-enhanced FIA translates into higher hemoglobin and ferritin without excess infection. Parallel arms with and without iron but identical prebiotic exposure would help disentangle prebiotic-driven from iron-driven microbiome changes. More granular metagenomic and metabolomic profiling could map specific metabolic pathways, including lactic acid and short-chain fatty acid production, to iron uptake and toxin gene dynamics. Dose-ranging studies around 3–7.5 g GOS/FOS may refine the minimal effective prebiotic dose compatible with locally acceptable cereal formulations.
Key takeaways for Researchers and Clinicians
This Kenyan infant trial shows that adding 3–7.5 g GOS/FOS to a low-dose ferrous fumarate cereal both increases fractional iron absorption (up to 60% versus baseline iron-only meal) and shifts gut ecology toward higher Lactobacillus, lower Enterobacteriaceae and pathogen gene burden, and reduced fecal pH and calprotectin. Effects were similar across prebiotic doses for FIA, while 7.5 g more clearly improved pH and calprotectin, and 3 g reduced toxin-encoding genes.
Methodologically, erythrocyte incorporation of 57Fe/58Fe-labelled FeFum meals combined with multi-omic fecal profiling provides a robust metallomic framework to link iron handling to microbiome structure and function. Clinically, iron fortification strategies in high-burden settings may be safer and more efficient when paired with specific prebiotics rather than simply escalating iron dose. Translationally, this work positions prebiotic–iron combinations as a promising lever to “shape” the infant metallome–microbiome axis for both efficacy and safety.
Citation
Mikulic N, Uyoga MA, Stoffel NU, et al. Prebiotics increase iron absorption and reduce the adverse effects of iron on the gut microbiome and inflammation: a randomized controlled trial using iron stable isotopes in Kenyan infants. Am J Clin Nutr. 2024;119(2):456–469. doi:10.1016/j.ajcnut.2023.11.018