Lactose and sucrose are two closely related sugars that your body can use to provide cells with energy. While they have many chemical similarities -- they even share the same chemical formula -- they're digested differently by the body. One major difference between the two is that while lactose intolerance is relatively common, sucrose intolerance is quite rare.
Lactose
Lactose, also called milk sugar, is a kind of chemical known as a disaccharide. This means it's a carbohydrate made up of two small sugar units, called glucose and galactose. All carbohydrates consist of small sugar units; those consisting of only one or two, like lactose, are called sugars and have a sweet taste, explain Drs. Mary Campbell and Shawn Farrell in their book "Biochemistry." Common sources of lactose include milk and dairy products.
Sucrose
Like lactose, sucrose is a disaccharide and a sugar. It's made up of two smaller sugars, called glucose and fructose. Sucrose tastes much sweeter than lactose because it binds more tightly to sweetness receptors on the human tongue. Despite its sweeter taste, sucrose contains the same number of calories as lactose. Sucrose is more commonly called table sugar, and common sources include fruits and foods that have had sugar added to them.
Digestion
Whether you consume lactose or sucrose, you need to break the disaccharides down into their smaller sugar components before you can absorb them. Your body accomplishes this using enzymes, which help chemical reactions take place more rapidly than they otherwise would, explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry." Once you've digested and absorbed the constituents of sucrose and lactose, your cells process the sugar units nearly identically and can either use them for energy or store them as fat.
Intolerance
It's not uncommon to be lactose intolerant, which means you can't digest lactose. This results from underproduction of lactase, the enzyme responsible for lactose digestion. It's most common in people of non-European descent and occurs more frequently in older people. Sucrase deficiencies, on the other hand, are quite rare. Sucrase is the enzyme that you use to digest sucrose. The Genetics Home Reference, a website maintained by the National Institutes of Health, estimates sucrase deficiency as occurring in one out of every 5,000 people.
References
- "Biochemistry"; Mary Campbell, Ph.D. and Shawn Farrell, Ph.D.; 2005
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
- Genetics Home Reference: Sucrase Deficiency
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