How are LCT and blood sugar related?

The relationship between the LCT gene and blood sugar is indirect, primarily mediated through lactose digestion. The LCT gene encodes lactase, the enzyme that breaks down lactose (milk sugar) into glucose and galactose. In individuals with lactase persistence (genetic variants that maintain lactase production into adulthood), consuming dairy leads to a moderate blood sugar rise from the released glucose. In lactose intolerance (lactase deficiency), undigested lactose reaches the colon and is fermented by bacteria – causing symptoms like bloating but no direct blood sugar increase. Some studies suggest that a low-lactose diet in intolerant individuals may improve glycemic control by removing this sugar source. However, evidence for a direct causal effect of LCT variants on fasting glucose or diabetes risk is weak. GWAS have linked LCT to lactose tolerance, not to blood sugar regulation. The clinical relevance for blood sugar is therefore low. Caveat: A genetic test for LCT does not predict current blood sugar levels or diabetes risk. For blood sugar issues, established markers like HbA1c and fasting glucose are more informative.