(P30-034-25) Impact of Plant-Based vs. Omnivorous Diets: Iron absorption and Gut Microbiota Interactions

Objectives: Iron (Fe) is an essential micronutrient for both humans and microbes. The human body tightly regulates non-heme Fe absorption based on iron status, while heme Fe uptake from animal foods remains unaffected. Unabsorbed Fe in the gut creates competition for Fe between the host and microbes which may further alter composition of the gut microbiota. With increasing adoption of plant-based diets and recommendations to reduce animal food consumption, understanding how dietary Fe sources and unabsorbed Fe affect gut microbiota and Fe absorption is crucial. This study explores the interplay between heme and non-heme Fe intake, iron absorption, and gut microbiota composition in adults.

Methods: We are studying vegetarian and non-vegetarian males and premenopausal, non-pregnant, non-lactating females aged 18–40 years, who are non-smokers and free of intestinal or other chronic diseases. Iron absorption was determined based on erythrocyte ⁵⁷Fe incorporation 2-weeks post-dosing measured by magnetic sector thermal ionization mass spectrometry. Iron status biomarkers, including serum ferritin (SF), were measured and habitual diet was evaluated using a 24-hour recall and food frequency questionnaire.

Results: Male non-vegetarians (n = 29) exhibited significantly higher SF concentrations compared to male vegetarians (n=9) (107.7 [81.9, 188.0] ng/mL vs. 51.2 [36.8, 71.2] ng/mL; p < 0.01), while SF concentrations in females were similar between dietary groups. Male vegetarians showed slightly higher Fe absorption rates (8.6 [4.7, 20.4] %) than non-vegetarians (8.0 [1.9, 16.8] %). No significant differences in Fe absorption were observed in females, despite vegetarians (n=15) consuming more dietary Fe than non-vegetarians (n=29) (17.2 [11.3, 21.1] mg/day vs. 11.6 [6.6, 13.9] mg/day; p < 0.05). As expected, SF was inversely correlated with Fe absorption in the group as a whole (p < 0.001, R²=0.35), and for non-vegetarians (R²=0.38) and vegetarians (R²=0.42).

Conclusions: Our preliminary findings indicate plant-based diets are associated with lower body Fe stores, particularly in males, with adaptative increases in Fe absorption efficiency. These changes may lead to variability in the load and composition of unabsorbed Fe in the gut, warranting further studies to evaluate the impact of these differences on the gut microbiota.

Funding Sources: USDA 2023-67017-39059