Lactose intolerance is a common digestive condition where individuals experience symptoms such as diarrhea, gas, abdominal pain, and bloating after consuming milk or milk-based products. These symptoms occur because the person has a deficiency in lactase, the enzyme required to break down lactose, the sugar found in milk. When lactose remains undigested in the intestine, it ferments under bacterial action, causing discomfort.

The Cause of Lactose Intolerance Symptoms

Lactose intolerance arises primarily due to a deficiency of the enzyme lactase located in the small intestine. Lactase breaks down lactose into simpler sugars, glucose and galactose, which can be easily absorbed. Without sufficient lactase:

• Lactose passes undigested into the colon.

• Colonic bacteria ferment lactose, producing gas (hydrogen, methane, carbon dioxide).

• The fermentation process increases water retention in the intestines, leading to diarrhea.

• The gas and increased intestinal contents cause abdominal pain, bloating, and flatulence.

Why Symptoms Disappear with Curd Consumption

Curd (yogurt) differs from milk because it contains live bacteria such as Lactobacillus species that produce the enzyme lactase. These bacteria help pre-digest lactose in curd before it reaches the intestine. Consequently:

• The lactose content in curd is partially broken down.

• The bacterial lactase helps digest lactose within the gut.

• This reduces lactose fermentation in the colon.

• Symptoms like diarrhea, gas, and pain mostly disappear.

Explanation of the Statements

• Statement A: Deficiency of intestinal sucrase-maltase is unrelated to milk intolerance because these enzymes digest other sugars (sucrose and maltose).

• Statement B: Correct that curd is not deficient in sucrose and maltose, but this doesn’t explain milk intolerance symptoms.

• Statement C: Correct as lactose intolerance is caused by a deficiency of intestinal lactase.

• Statement D: Correct because bacteria in curd contain lactase, aiding lactose digestion.

Conclusion

The symptoms after milk consumption are caused by lactose intolerance due to lactase deficiency (Statement C). The improvement on consuming curd is because bacteria in curd provide lactase (Statement D) that helps digest lactose. Therefore, the correct explanation is (4) C and D.