Disaccharides are a type of carbohydrate, commonly known as “double sugars,” that play a role in human nutrition. They are important energy sources found in a wide variety of foods.
Building Blocks of Disaccharides
Disaccharides form when two single sugar units, called monosaccharides, link together. Monosaccharides, such as glucose, fructose, and galactose, are the simplest form of sugar. These units connect through a chemical bond known as a glycosidic bond.
This bond forms when a water molecule is removed as two monosaccharides join. This linkage creates a larger sugar molecule, and the specific arrangement of these bonds gives each disaccharide unique characteristics.
Key Disaccharides in Our Diet
Three common disaccharides in the human diet are sucrose, lactose, and maltose. Each is composed of a distinct pair of monosaccharides.
Sucrose, or table sugar, forms from one glucose and one fructose molecule. It is present in many plants and extracted from sugarcane and sugar beets. Lactose, or milk sugar, consists of one glucose and one galactose molecule, found in the milk of all mammals. Maltose, or malt sugar, is made of two glucose molecules. It is less common naturally but forms during starch digestion.
How Our Bodies Process Disaccharides
The body cannot directly absorb disaccharides because they are too large. They must be broken down into individual monosaccharide units during digestion. This process, called hydrolysis, involves adding a water molecule to cleave the glycosidic bond.
Specific enzymes, called disaccharidases, perform this task in the small intestine. Lactase breaks down lactose into glucose and galactose. Sucrase digests sucrose into glucose and fructose, while maltase breaks maltose into two glucose molecules. Once broken down, these monosaccharides are absorbed into the bloodstream for energy or storage.
Common Dietary Sources
Disaccharides are present in many foods, either naturally or as added ingredients. Sucrose is found in fruits like bananas, mangoes, and oranges, and vegetables such as sweet potatoes and carrots. It is also the primary component of granulated sugar, maple syrup, and processed sweets like cakes and chocolates.
Lactose is found predominantly in dairy products, including milk, cheese, yogurt, and ice cream. Processed foods like cereals, baked goods, and some sauces can also contain lactose if they include dairy ingredients.
Maltose is present in grains like wheat, barley, and cornmeal. It is found in breads, breakfast cereals, molasses, and some malted beverages. Cooked sweet potatoes are another source of maltose.