Myths vs facts: SHBG and gut health

SHBG (sex hormone-binding globulin) is primarily produced in the liver and regulated by insulin, thyroid hormones, and estrogens. A link to gut health is hypothesized via the gut–liver axis: the microbiome produces short-chain fatty acids (e.g., butyrate) that improve insulin sensitivity, potentially lowering SHBG. Additionally, pro-inflammatory gut bacteria may impair liver function and reduce SHBG production. However, direct human evidence is weak – most data come from animal models or cross-sectional associations. Low SHBG is better understood as a marker of metabolic syndrome, insulin resistance, or fatty liver than as a specific indicator of gut health. Consumer DNA tests that claim SHBG reflects 'gut health' often overstate causal relationships. The fact is: SHBG is a versatile but non-specific biomarker. A fiber-rich diet can benefit both the microbiome and SHBG levels, but a proven causal chain from gut health to SHBG remains unestablished. Evidence is mechanistic and mixed.