The FeMicrobiome study will evaluate gut microbiome features and their relationships with dietary iron absorption in healthy adults. The investigators hypothesize that (1) the gut microbiota can be shaped by the heme and non-heme Fe content of the diet and that (2) this will influence individual variation in dietary Fe absorption.

Iron is an essential micronutrient ingested as either heme iron (from animal products) or non-heme iron (from both plant and animal sources). Humans have no regulatable means of eliminating absorbed iron, necessitating tight control of dietary iron absorption. Likewise, native microbes have evolved efficient iron sensing and utilization pathways to scavenge iron from the gastrointestinal environment, resulting in a competition for iron between the host and their microbiota. As growing numbers of Americans adopt plant-based diets, heme iron intakes are markedly reduced. This may shift the gut microbiome as some gut microbiota cannot independently synthesize heme and require host dietary heme sources to support their heme-dependent functions. Animal data have recently discovered that other gut microbiota respond to a low iron. To date, significant knowledge gaps exist on the interplay between dietary iron sources, native gut microbes, and iron utilization in humans. In the FeMicrobiome study, study investigators will recruit 120 adults who habitually ingest plant-based diets or habitually ingest diets containing animal protein (e.g., beef, pork, chicken, fish, and seafood). Iron absorption will be measured by using an in vivo, functional approach based on stable iron isotopes (i.e., 57Fe). Study participants will consume 57Fe (as ferrous sulfate) in the fasted state followed by two standardized meals. Two weeks after iron dosing, a blood sample will be collected from each participant and the amount of 57Fe incorporated into red blood cells will be measured using magnetic sector thermal ionization mass spectrometry. A stool sample will be collected near the time of 57Fe consumption. DNA will be extracted from this stool sample and sequenced using a high-depth shotgun metagenomic approach.

Inclusion Criteria:

• Healthy adults
• Age between 18- 40y
• Non-smoking
• Not currently taking vitamin, mineral, prebiotic, and probiotic supplements.
• Females: premenopausal and not pregnant or lactating
• No preexisting medical complications (such as eating disorders, hemoglobinopathies, malabsorption diseases, steroid use, substance abuse history, or taking medications known to influence iron homeostasis)
• Body mass index (BMI) between 18 - 27 kg/m2.

Exclusion Criteria:

• BMI <18 or > 27 kg/m2,
• Age <18 y or > 40y,
• Smoking
• Pregnancy, lactating
• Have gastrointestinal disorders/malabsorption diseases/hemoglobinopathies/dietary restrictions/steroid use/ medication use of medications known to impact iron status, iron utilization or inflammatory status
• Currently take vitamin, mineral, prebiotic, and probiotic supplements.
• Recently received antibiotic treatment

120 healthy adults who habitually consume plant-based diets or habitually consume diets containing animal protein