Evidence check: Leaky Gut Test in the context of fatigue

So-called 'leaky gut' tests (e.g., zonulin, LPS, IgG against gut bacteria) are often marketed as a cause of fatigue. However, the scientific evidence is weak: zonulin in stool or serum is not a validated clinical marker for increased intestinal permeability, and a causal link to fatigue has not been established. Fatigue has many causes (sleep deprivation, iron deficiency, thyroid function, psychological factors) that should be evaluated before gut diagnostics. These tests are primarily based on marketing rather than robust human studies. Similar to IgG food intolerance tests (see context), they often lead to unnecessary dietary restrictions without proven benefit. Caveat: self-interpretation can lead to malnutrition or delay of a proper diagnosis. Evidence: marketing.