How are IgG Unverträglichkeitstest and fatigue related?

IgG food intolerance tests (e.g., measuring IgG4 against foods) are often marketed as a way to identify foods that cause fatigue, but the scientific evidence for a causal link is weak. These tests detect normal immune responses to foods, not true intolerances. Most studies show that IgG-based elimination diets produce only subjective improvements, largely due to placebo effects. Major allergy and immunology societies (e.g., EAACI, DGAKI) recommend against using IgG tests for diagnosing food intolerances. Fatigue is a multifactorial symptom that can stem from iron deficiency, sleep disorders, thyroid issues, stress, or other medical conditions. Relying on an IgG test may delay proper diagnosis. If you are experiencing persistent fatigue, consult a healthcare provider for a thorough evaluation. The evidence for IgG testing in this context is 'mixed/unclear', with strong marketing but weak clinical support.