Sigma Nutrition Radio #417: Austin Baraki, MD – What Do Nutrient Blood Tests Actually Tell Us?: Understanding Biomarkers
Dec 14, 2021
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Why Blood Calcium Misleads About Dietary Calcium
- Serum calcium rarely reflects dietary calcium because >99% of body calcium is in bone and only ~1% is in blood.
- Blood calcium is partly albumin-bound and ionized; hydration, pH, albumin and handling alter results, so interpretation is complex.
What Makes A Valid Nutritional Biomarker
- A good nutritional biomarker must be sensitive to intake, have a short half-life, and be unaffected by other diseases or physiologic states.
- Many commonly measured blood markers fail these criteria and shouldn't be used as direct nutritional status indicators.
Prefer Recovery Markers And Match Tissue To Timeframe
- Use recovery biomarkers (e.g., 24‑hour urinary sodium) to assess intake when possible because they directly reflect excretion of consumed nutrient.
- Choose tissue compartment by time integration: serum (days), RBC (≈3 months), adipose (months–years).