What role does IgG play in fatigue?

The role of IgG in fatigue is not clearly established. IgG antibodies are part of the adaptive immune system and indicate a long-term immune response, such as in chronic infections or autoimmune diseases. Elevated IgG levels can be observed in conditions like chronic fatigue syndrome (ME/CFS) or post-COVID syndrome, but causality remains uncertain. IgG testing for food sensitivities is not recommended by major medical organizations because it often yields false positives and lacks proven clinical benefit. The evidence for a direct link between IgG and fatigue is weak and mostly mechanistic. Routine IgG screening for fatigue is not indicated. Instead, other causes such as iron deficiency, thyroid dysfunction, or sleep disorders should be evaluated by a physician. MyBody-X tests measuring IgG are lifestyle products without medical approval. Caveat: IgG levels alone are not a reliable marker for fatigue.