Disaccharides

Disaccharides are sugars made of two sugar units joined together. The three common ones are sucrose (table sugar), lactose (milk sugar) and maltose (malt sugar). Enzymes in the small intestine split each one into single sugars before it is absorbed.

What is it?

"Di" means two. Sucrose is glucose plus fructose, lactose is glucose plus galactose, and maltose is two glucose units. Each is split by its own enzyme at the surface of the small intestine: sucrase, lactase and maltase. If an enzyme is missing or low, the sugar passes to the large intestine where bacteria ferment it, causing gas, bloating and loose stools — as in lactose intolerance.

See Sucrose, Lactose and Maltose, and the single sugars in Monosaccharides.

What it does

1. Provide energy once split into glucose, fructose or galactose, at about 4 kilocalories per gram
2. Make food taste sweet
3. Lactose in milk is the main carbohydrate for infants
4. Maltose forms when starch is digested, and when grains are malted

Food sources

Sucrose: table sugar, sweets, desserts and sweet drinks. Lactose: milk, yoghurt and soft cheese. Maltose: malted drinks, malt extract, maltose syrup, sprouted grains and beer. Fruit and vegetables contain some sucrose.

Singapore food examples

1. Sucrose in sweet drinks, kueh, gula melaka and kaya
2. Lactose in milk, yoghurt, ice cream and creamy desserts
3. Maltose in malted drinks, maltose candy and barley-based foods
4. Order "kosong" (no sugar) or "siew dai" (less sugar) for kopi and teh
5. Check the Nutri-Grade label on drinks

How much do I need?

There is no recommended intake for this sugar on its own, and Singapore's RDA table does not list it. Singapore's dietary guidelines advise that added sugar provide no more than 10 percent of daily energy — about 10 teaspoons (around 50 g) on a 2,000-kilocalorie diet, with about 5 teaspoons (25 g) even better — see Singapore's dietary guidelines for adults (HealthHub).

Low intake and deficiency

There is no deficiency; the body does not need disaccharides specifically. Being unable to digest one of them (most often lactose) causes symptoms but is not a nutrient deficiency, though avoiding dairy altogether can lower calcium intake.

Too much and safety

Large amounts of free sucrose, mostly from sweet drinks, are linked to weight gain, tooth decay, fatty liver and type 2 diabetes. Disaccharide intolerance, especially lactose intolerance, causes bloating, cramps, gas and diarrhoea after eating the sugar; adjust portions or use lactose-free products.

Absorption and bioavailability

Disaccharides cannot be absorbed whole. Sucrase, lactase and maltase on the lining of the small intestine split them into monosaccharides, which are then absorbed. Lactase falls after childhood in most people worldwide, including most adults in East and Southeast Asia, while sucrase and maltase stay active.

Connection to daily life

1. Dental health: sucrose is the sugar most linked to tooth decay; limit how often you have sweet things
2. Digestive comfort: if dairy upsets your stomach, try smaller portions, yoghurt, hard cheese or lactose-free milk
3. Weight and blood sugar: cutting sweet drinks is one of the simplest changes with a large effect
4. Related: see Carbohydrates and Sugars

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)