LCT and Diarrhea: If lactase deficiency or activity is reduced, it can lead to the symptoms of diarrhea, gastrointestinal distention, and abdominal pain.10 Studies have shown that various diarrheal diseases are closely related to lactase activity, including diarrhea-predominant irritable bowel syndrome, persistent diarrhea, and antibiotics-associated diarrhea (AAD).11-14 Meanwhile, lactase has been linked to digestive disorders.