Effects of the Mediterranean Diet, Ketogenic Diet, and Intermittent Fasting on Iron Metabolism and Iron Deficiency Risk in Adults with Obesity: A Systematic Literature Review

Background/Objectives: Obesity is paradoxically associated with iron deficiency despite adequate dietary intake, driven by chronic inflammation and elevated hepcidin. Different dietary patterns may differentially affect iron metabolism in obese individuals, yet comparative evidence remains limited. Methods: We conducted a systematic literature review following PRISMA 2020 guidelines. Four databases (SciSpace, Google Scholar, PubMed) were searched through 2025 using terms related to obesity, iron deficiency, and three dietary patterns: Mediterranean diet, ketogenic diet, and intermittent fasting. Studies were screened using seven predefined criteria (three inclusion, four exclusion) with thresholds of ≥4.0/5.0 for abstract screening and ≥4.5/5.0 for full-text screening. Results: From 396 identified records (SciSpace n = 325, Google Scholar n = 57, PubMed n = 14), 38 studies were included after removing 62 duplicates and screening 334 unique records. Studies without accessible full text were excluded.The Mediterranean diet appears most protective for iron status due to its anti-inflammatory profile (omega-3 fatty acids, polyphenols, vitamin C) and bioavailable iron sources. Ketogenic diets may impair duodenal iron absorption through hepcidin-independent mechanisms and restrict dietary iron diversity. Intermittent fasting shows complex effects, remodeling iron metabolism with increased transferrin and decreased ferritin within physiological ranges. Weight loss per se consistently improves iron status by reducing adipose-driven inflammation and lowering hepcidin. Conclusions: Among the three dietary patterns examined, the Mediterranean diet appears most protective for iron status in obese individuals. The ketogenic diet may pose the highest risk due to restricted dietary iron diversity and potential hepcidin-independent absorption impairment. Direct comparative randomized controlled trials are urgently needed. Clinicians should routinely monitor iron biomarkers, including hepcidin, in obese patients undertaking any dietary intervention. Quantitative biomarker data from the 38 included studies showed serum ferritin reductions of 8–28%, hemoglobin levels remaining within clinically stable ranges, and IL-6 decreases of 15–42% across dietary patterns.