What role does FUT2 play in fatigue?

The role of the FUT2 gene (secretor status) in fatigue is not clearly established. FUT2 determines whether you express ABO antigens on mucosal surfaces and in body fluids (secretor vs. non-secretor). Non-secretors have altered gut microbiota composition and a higher risk of vitamin B12 deficiency, which could indirectly contribute to fatigue. Some observational studies have linked FUT2 variants to chronic fatigue, but no robust interventional trials exist. The effect size is small, and clinical relevance remains uncertain. A single genetic test cannot explain fatigue – other factors (iron, sleep, stress, thyroid) are far more important. Evidence: unclear. Caveat: consumer tests often overstate single-gene effects.