How are LCT and Darmgesundheit related?

The relationship between LCT (lactase gene) and gut health is well-established. LCT encodes the lactase enzyme, which breaks down lactose (milk sugar) in the small intestine. Variants such as rs4988235 (LCT-13910 C/T) determine whether lactase production persists into adulthood (lactase persistence) or declines (lactase non-persistence). In lactase non-persistence, undigested lactose reaches the colon, where it is fermented by gut bacteria, producing gas and short-chain fatty acids. This can cause bloating, diarrhea, abdominal pain, and alter the gut microbiota composition (e.g., increase in gas-producing bacteria). Over time, a high-lactose diet in intolerant individuals may stress the gut barrier and mimic or exacerbate irritable bowel syndrome (IBS) symptoms. The evidence is human-strong: numerous clinical studies and guidelines (e.g., AGA, DGVS) confirm this link. However, lactose intolerance is a genetic trait, not a disease. Genetic testing for LCT can guide dietary adjustments but does not replace medical evaluation for persistent GI issues. Effect sizes are moderate to large, but individual tolerance varies.