What is Fructose Malabsorption?
Fructose is a sugar found naturally in many foods, in several forms: as a free sugar; as a constituent of the disaccharide sucrose; or as fructans, a polymer of fructose present in some fruits, vegetables and grains. Normally fructose is absorbed in the small intestine, via two mechanisms. Firstly, free fructose is facilitated by a low capacity transporter, GLUT-5, that is present throughout the small intestine. Secondly, when glucose is present with fructose, it is taken up more effectively, a response believed to be related to the GLUT-2 transporter.
Most people can absorb fructose, however one in three adults with symptoms of IBS malabsorb fructose. In fructose malabsorption the absorption of free fructose (in excess of glucose) is impaired. Failure to completely absorb free fructose leads to its delivery in the colon. Colonic bacteria rapidly ferment this free fructose to hydrogen, carbon dioxide and short-chain fatty acids. This can cause symptoms of IBS such as bloating, excessive flatulence, borborygymi, abdominal pain, loose bowels motions and/or constipation.
Fructose malabsorption can be diagnosed using hydrogen/methane breath testing, which recognises unabsorbed fructose, and dietary strategies can assist with minimising symptoms of Fructose Malabsorption.