Lactose

Lactose is the main sugar in milk, made of one glucose and one galactose unit. It is the main carbohydrate in breast milk and infant formula. Many adults, including most people of East and Southeast Asian descent, make less of the enzyme that digests it, which can cause gas, bloating and loose stools.

What is it?

Lactose is a disaccharide, also called milk sugar. Cow's milk has about 4.7 g per 100 ml and human milk about 7 g per 100 ml. The enzyme lactase, on the lining of the small intestine, splits it into glucose and galactose for absorption.

Most people worldwide make less lactase after childhood (lactase non-persistence), including a majority of adults in East and Southeast Asia. This is normal, not a disease. Lactose intolerance is when low lactase causes symptoms; a milk allergy is a different condition, caused by the immune system reacting to milk protein.

What it does

1. Provides energy at about 4 kilocalories per gram
2. Is the main carbohydrate for infants and young children
3. May help absorption of calcium and support gut bacteria such as Bifidobacteria
4. Has a low glycaemic index (about 45), as digestion and absorption of the glucose and galactose are slower

Food sources

Milk (fresh, evaporated, powdered), yoghurt, soft cheese, ice cream, cream and many processed foods that contain milk solids or whey, including some bread, sauces and medicines. Hard, aged cheeses (Cheddar, Parmesan) and butter contain very little, and yoghurt is often better tolerated than milk because bacteria in it help digest lactose.

Singapore food examples

1. Milk, evaporated and condensed milk in kopi, teh and desserts
2. Yoghurt and lassi (often better tolerated than milk)
3. Ice cream, milk-based desserts and milk tea
4. Hard cheeses with very little lactose
5. Lactose-free milk, soy milk and other fortified plant milks
6. Check labels for milk, whey and milk powder in processed foods

How much do I need?

There is no recommended intake for lactose, and Singapore's RDA table does not list it. Dairy is a key source of calcium, which Singapore's RDA does list — 800 mg a day for adults 19 to 50 and 1,000 mg after — see Singapore's age- and sex-specific Recommended Dietary Allowances (HealthHub). If you avoid lactose, get calcium from other foods.

Low intake and deficiency

There is no deficiency of lactose. If you avoid dairy because of lactose intolerance, make sure you get enough calcium, vitamin D, protein and vitamin B12 from other foods, such as calcium-set tofu, fortified soy milk, small fish eaten with bones, kai lan and fortified products.

Too much and safety

Lactose intolerance causes bloating, cramps, gas, loud stomach noises and diarrhoea, usually 30 minutes to 2 hours after dairy. The amount that causes symptoms varies: many people tolerate up to about 12 g (roughly one cup of milk) in a day, especially with meals. It is not harmful, and the condition is not an allergy.

Try smaller portions of dairy with food, choose yoghurt, hard cheese or lactose-free milk, and use lactase enzyme drops or tablets. See a doctor if you have severe symptoms, blood in the stool, weight loss or symptoms in infants.

Absorption and bioavailability

Lactose must be split by lactase before it can be absorbed. Undigested lactose passes to the colon, where bacteria ferment it to gas and short-chain fatty acids, and draw water into the bowel. Lactose-free milk has lactase added, and is as nutritious as regular milk.

Connection to daily life

1. Bone health: if you cut dairy, get calcium and vitamin D from other sources — see Calcium and Vitamin D
2. Digestive comfort: small portions, yoghurt and lactose-free options let many people keep dairy
3. Infants: lactose is a normal part of breast milk and formula
4. Related: see Galactose and Glucose

Sources: 1. HealthHub Singapore — Dietary guidelines for adults: https://www.healthhub.sg/well-being-and-lifestyle/food-diet-and-nutrition/dietary_guidelines_adults 2. HealthHub Singapore — Recommended Dietary Allowances: https://www.healthhub.sg/well-being-and-lifestyle/food-diet-and-nutrition/recommended_dietary_allowances 3. Health Promotion Board — Singapore Food Insights Database (SG FoodID): https://www.hpb.gov.sg/healthy-living/food-and-beverage/sgfoodid/ 4. FAO/INFOODS — Food composition tables and databases: https://www.fao.org/food-composition/tables-and-databases/en/ 5. National Academies of Sciences, Engineering, and Medicine — Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (2005)