What is fructose?

Now, some facts about fructose, what it is and how the human body (usually) absorbs it.

Fructose is a naturally occurring sugar, a so-called monosaccharide or a single sugar. It belongs to the poorly absorbable short-chain carbohydrates, also known as FODMAPs (Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols). Lactose, fructans, sorbitol, and mannitol are further examples of FODMAPs.

You can find fructose in most fruits, honey, some vegetables and in table sugar (sucrose). As it is sweeter than glucose, it is unfortunately used in many processed foods and beverages, although it is no essential nutrient for a human.

There are two ways of absorbing fructose:

The first way is slow but specific for fructose. Fructose is normally absorbed along the entire small intestine with the aid of a specific protein called GLUT5. The second is fast but occurs only together with glucose, which acts as a “piggyback” transport. A rule of thumb states that one molecule of glucose enables the absorption of one molecule of fructose.

This means, that fructose in excess of glucose is potentially malabsorbed if the GLUT5 fructose transporter is not efficient enough or the transit of fructose along the small bowel is too fast.



