Which carbohydrate is the primary sugar in milk?

• A. Glucose
• B. Lactose
• C. Maltose
• D. Sucrose

Answer: (B)

Milk’s primary carbohydrate is lactose, a disaccharide formed from glucose and galactose. It’s produced in the mammary gland and released into milk as the dominant sugar, present at about 4–5 grams per 100 milliliters in cow’s milk (the exact amount varies by species and diet). That makes lactose the main carbohydrate that dairy science and nutrition refer to when talking about milk sugar.

Glucose is a simple sugar that you’ll encounter in many foods, but in milk it mostly appears as part of lactose rather than as free glucose. Maltose is another disaccharide, but it comes from starch breakdown and is not a typical component of milk. Sucrose, the common table sugar, is a plant-derived disaccharide and is not produced in significant amounts in milk. Hence, lactose stands out as the primary carbohydrate in milk, and that’s why it’s the term you’ll see when discussing milk sugar. Lactose intolerance and lactase enzyme activity are related concepts because they affect the digestion of this specific milk sugar.