由于血红素铁非常有利于人体吸收，而素食中的铁不利于人体吸收。因此，当人体戒断血红素铁后——吃素后，需要有一个适应期。
很多人刚吃素后会感到浑身没有劲等其他缺铁的症状，因而产生种种疑惑。但其实这是人体对戒断血红素铁(肉食中的铁)的正常反应。由于血红素铁非常有利于人体吸收，而素食中的铁不利于人体吸收。因此，当人体戒断血红素铁后——吃素后，需要有一个适应期。
首先，我们需要知道，过量的铁对人体有很大的毒性，一些研究显示，血红素铁显著增加心血管死亡风险，及2型糖尿病和某些癌症风险。因此人体对铁吸收的管理非常严格，当人体监测到体内铁过量时可在几小时内做出反应，通过肝脏产生的肽激素 hepcidin 来迅速抑制铁的吸收。但是，当人体缺铁时，通常需要3-5天才做出反应，以提高铁的吸收。这是人体的一种保护机制，需要确认人体在持续缺铁时，才做出反应。显然，人体宁愿冒缺铁的风险也不愿意冒铁过量的风险。
这提示我们，血红素铁只是肉食的营养优势，而并非健康优势，或者说是健康劣势。如果营养是为健康服务，而非为了营养而营养(显而易见)，那么，肉食中的血红素铁其实是肉食的一大缺陷。实际上，我们更应该对铁过量感到恐惧，而不是对缺铁感到恐惧
此外，人体对铁吸收的调整能力很强。例如，当人体铁的储存较低时，通过降低肽激素 hepcidin 可以使铁的吸收增加10-20倍[21]。因此，我们对缺铁也不必过度担忧，除非你的调节能力有问题。
人体除了通过肽激素 hepcidin 来系统性地调整铁的吸收以外，还需要调整许多其他生物机制来使铁的吸收最终适应，包括肠道铁转运蛋白、肠道环境等。当人体缺铁时，例如，刚刚放弃肉食转为素食者，视不同的机制可能需要较长的适应期，从几天(如肽激素 hepcidin)到几周[11]，十周[33](吸收率初步提升)，到六个月或更长[3](最终稳定优化)。因此，在上述适应期内，可能会有相当多的人出现缺铁的症状，需要积极调整饮食结构来应对，部分人可能需要在医生指导下服用铁补充剂。
但是，即使在适应期内出现缺铁症状，依然不建议盲目服用铁补充剂。因为铁补充剂本身会抑制身体对铁的吸收(原理同戒断肉食类似)。最好的方法是积极调整饮食结构，让身体顺利度过适应期。除非有很高的贫血风险的，或高强度的运动员等，可以在医生指导下服用，必要时可以采用间隔服用(如每周2-3次)的策略。
参考资料(由 Grok 4 整理)：
[1] ROSE S D. Ensuring Adequate Iron Status in Vegetarians and Vegans[J/OL]. Advanced Research in Gastroenterology & Hepatology, 2019, 13(4)[2025-07-20]. https://juniperpublishers.com/argh/ARGH.MS.ID.555867.php. DOI:10.19080/argh.2019.13.555867.
[2] NEBL J, SCHUCHARDT J P, WASSERFURTH P, 等. Characterization, dietary habits and nutritional intake of omnivorous, lacto-ovo vegetarian and vegan runners – a pilot study[J/OL]. BMC Nutrition, 2019, 5(1)[2025-07-20]. https://bmcnutr.biomedcentral.com/articles/10.1186/s40795-019-0313-8. DOI:10.1186/s40795-019-0313-8.
[3] LÓPEZ‐MORENO M, VIÑA I, MARRERO‐FERNÁNDEZ P, 等. Dietary Adaptation of Non‐Heme Iron Absorption in Vegans: A Controlled Trial[J/OL]. Molecular Nutrition & Food Research, 2025, 69(12)[2025-07-20]. https://onlinelibrary.wiley.com/doi/10.1002/mnfr.70096. DOI:10.1002/mnfr.70096.
[4] VAN WONDEREN D, MELSE-BOONSTRA A, GERDESSEN J C. Iron Bioavailability Should be Considered when Modeling Omnivorous, Vegetarian, and Vegan Diets[J/OL]. The Journal of Nutrition, 2023, 153(7): 2125-2132. DOI:10.1016/j.tjnut.2023.05.011.
[5] SLYWITCH E, SAVALLI C, DUARTE A C G, 等. Iron Deficiency in Vegetarian and Omnivorous Individuals: Analysis of 1340 Individuals[J/OL]. Nutrients, 2021, 13(9): 2964. DOI:10.3390/nu13092964.
[6] FAIRWEATHER-TAIT S. The role of meat in iron nutrition of vulnerable groups of the UK population[J/OL]. Frontiers in Animal Science, 2023, 4[2025-07-20]. https://www.frontiersin.org/articles/10.3389/fanim.2023.1142252/full. DOI:10.3389/fanim.2023.1142252.
[7] HAIDER L M, SCHWINGSHACKL L, HOFFMANN G, 等. The effect of vegetarian diets on iron status in adults: A systematic review and meta-analysis[J/OL]. Critical Reviews in Food Science and Nutrition, 2018, 58(8): 1359-1374. DOI:10.1080/10408398.2016.1259210.
[8] ŚLIWIŃSKA A, LUTY J, ALEKSANDROWICZ-WRONA E, 等. Iron status and dietary iron intake in vegetarians[J/OL]. Advances in Clinical and Experimental Medicine, 2018, 27(10): 1383-1389. DOI:10.17219/acem/70527.
[9] HUNT J R, ROUGHEAD Z K. Nonheme-iron absorption, fecal ferritin excretion, and blood indexes of iron status in women consuming controlled lactoovovegetarian diets for 8 wk[J/OL]. The American Journal of Clinical Nutrition, 1999, 69(5): 944-952. DOI:10.1093/ajcn/69.5.944.
[10] SAUNDERS A V, CRAIG W J, BAINES S K, 等. Iron and vegetarian diets[J/OL]. Medical Journal of Australia, 2013, 199(S4)[2025-07-20]. https://onlinelibrary.wiley.com/doi/abs/10.5694/mja11.11494. DOI:10.5694/mja11.11494.
[11] HUNT J R. Bioavailability of iron, zinc, and other trace minerals from vegetarian diets[J/OL]. The American Journal of Clinical Nutrition, 2003, 78(3): 633S-639S. DOI:10.1093/ajcn/78.3.633s.
[12] LÓPEZ-MORENO M, CASTILLO-GARCÍA A, ROLDÁN-RUIZ A, 等. Plant-Based Diet and Risk of Iron-deficiency Anemia. A Review of the Current Evidence and Implications for Preventive Strategies[J/OL]. Current Nutrition Reports, 2025, 14(1)[2025-07-20]. https://link.springer.com/10.1007/s13668-025-00671-y. DOI:10.1007/s13668-025-00671-y.
[13] NEMETH E, GANZ T. Hepcidin and Iron in Health and Disease[J/OL]. Annual Review of Medicine, 2023, 74(1): 261-277. DOI:10.1146/annurev-med-043021-032816.
[14] CORRENTI M, GAMMELLA E, CAIRO G, 等. Iron Absorption: Molecular and Pathophysiological Aspects[J/OL]. Metabolites, 2024, 14(4): 228. DOI:10.3390/metabo14040228.
[15] GANZ T, NEMETH E. Hepcidin and iron homeostasis[J/OL]. Biochimica et Biophysica Acta (BBA) - Molecular Cell Research, 2012, 1823(9): 1434-1443. DOI:10.1016/j.bbamcr.2012.01.014.
[16] GANZ T, NEMETH E. Regulation of iron acquisition and iron distribution in mammals[J/OL]. Biochimica et Biophysica Acta (BBA) - Molecular Cell Research, 2006, 1763(7): 690-699. DOI:10.1016/j.bbamcr.2006.03.014.
[17] CAMASCHELLA C, NAI A, SILVESTRI L. Iron metabolism and iron disorders revisited in the hepcidin era[J/OL]. Haematologica, 2020, 105(2): 260-272. DOI:10.3324/haematol.2019.232124.
[18] QIU L, FRAZER D M, HU M, 等. Mechanism and regulation of iron absorption throughout the life cycle[J/OL]. Journal of Advanced Research, 2025[2025-07-20]. https://linkinghub.elsevier.com/retrieve/pii/S2090123225000025. DOI:10.1016/j.jare.2025.01.002.
[19] YANG W, PENG M, WANG Y, 等. Deletion of hepcidin disrupts iron homeostasis and hematopoiesis in zebrafish embryogenesis[J/OL]. Development, 2025, 152(7)[2025-07-20]. https://journals.biologists.com/dev/article/152/7/dev204307/367595/Deletion-of-hepcidin-disrupts-iron-homeostasis-and. DOI:10.1242/dev.204307.
[20] FLORES S R L, NELSON S, WOLOSHUN R R, 等. Intestinal iron absorption is appropriately modulated to match physiological demand for iron in wild-type and iron-loaded Hamp (hepcidin) knockout rats during acute colitis[J/OL]. PLOS ONE, 2021, 16(6): e0252998. DOI:10.1371/journal.pone.0252998.
[21] PISKIN E, CIANCIOSI D, GULEC S, 等. Iron Absorption: Factors, Limitations, and Improvement Methods[J/OL]. ACS Omega, 2022, 7(24): 20441-20456. DOI:10.1021/acsomega.2c01833.
[22] DARSHAN D. Liver-gut axis in the regulation of iron homeostasis[J/OL]. World Journal of Gastroenterology, 2007, 13(35): 4737. DOI:10.3748/wjg.v13.i35.4737.
[23] ATANASIU V, MANOLESCU B, STOIAN I. Hepcidin – central regulator of iron metabolism[J/OL]. European Journal of Haematology, 2007, 78(1): 1-10. DOI:10.1111/j.1600-0609.2006.00772.x.
[24] COLLINS J F, WESSLING-RESNICK M, KNUTSON M D. Hepcidin Regulation of Iron Transport[J/OL]. The Journal of Nutrition, 2008, 138(11): 2284-2288. DOI:10.3945/jn.108.096347.
[25] GANZ T. Hepcidin and iron regulation, 10 years later[J/OL]. Blood, 2011, 117(17): 4425-4433. DOI:10.1182/blood-2011-01-258467.
[26] NICOLAS G, CHAUVET C, VIATTE L, 等. The gene encoding the iron regulatory peptide hepcidin is regulated by anemia, hypoxia, and inflammation[J/OL]. Journal of Clinical Investigation, 2002, 110(7): 1037-1044. DOI:10.1172/jci15686.
[27] GANZ T, NEMETH E. Iron imports. IV. Hepcidin and regulation of body iron metabolism[J/OL]. American Journal of Physiology-Gastrointestinal and Liver Physiology, 2006, 290(2): G199-G203. DOI:10.1152/ajpgi.00412.2005.
[28] FRAZER D M, WILKINS S J, BECKER E M, 等. Hepcidin expression inversely correlates with the expression of duodenal iron transporters and iron absorption in rats[J/OL]. Gastroenterology, 2002, 123(3): 835-844. DOI:10.1053/gast.2002.35353.
[29] KARCZEWSKI M, SIMIC S, SALEH L, 等. The magnitude of the plasma hepcidin response to oral iron supplements depends on the iron dosage[J/OL]. Swiss Medical Weekly, 2024, 154(2): 3635. DOI:10.57187/s.3635.
[30] SHARP P A. Intestinal Iron Absorption: Regulation by Dietary & Systemic Factors[J/OL]. International Journal for Vitamin and Nutrition Research, 2010, 80(45): 231-242. DOI:10.1024/0300-9831/a000029.
[31] MORETTI D, GOEDE J S, ZEDER C, 等. Oral iron supplements increase hepcidin and decrease iron absorption from daily or twice-daily doses in iron-depleted young women[J/OL]. Blood, 2015, 126(17): 1981-1989. DOI:10.1182/blood-2015-05-642223.
[32] FRAZER D M. Delayed hepcidin response explains the lag period in iron absorption following a stimulus to increase erythropoiesis[J/OL]. Gut, 2004, 53(10): 1509-1515. DOI:10.1136/gut.2003.037416.
[33] HUNT J R, ROUGHEAD Z K. Adaptation of iron absorption in men consuming diets with high or low iron bioavailability[J/OL]. The American Journal of Clinical Nutrition, 2000, 71(1): 94-102. DOI:10.1093/ajcn/71.1.94.
