Important Notice: Fructose malabsorption (formerly called dietary fructose intolerance) is not to be confused with hereditary fructose intolerance (HFI). They are very different conditions. Hereditary fructose intolerance (HFI), or fructose poisoning is a potentially fatal condition of the liver. It is a hereditary condition caused by a deficiency of liver enzymes that metabolize fructose. Consuming fructose can lead to all kinds of complications including jaundice, kidney failure and even death in those who are HFI.

Fructose malabsorbtion (FM), formerly known as "dietary fructose intolerance," is a digestive disorder of the small intestine. Fructose malabsorption is a digestive disorder in which deficient fructose carriers in the small intestine's enterocytes impair absorption of fructose. This leads to an excessive concentration of fructose in the intestines causing abdominal bloating, diarrhea and/or constipation. When an individual has FM there intestines cannot absorb even small amounts of fructose. When fructose is not absorbed properly in the small intestine, the unabsorbed fructose is osmotically reduced and normal colonic bacteria to short chain fatty acids and gases hydrogen, carbon dioxide and methane in the large intestine metabolize the absorption of water. This causes osmotic diarrhea, flatulence and bloating. The osmotic load itself might also have a laxative effect similar to that utilized by the commonly used disaccharide laxative lactulose. Osmotic diarrhea occurs when too much water is drawn into the bowels.

Unabsorbed fructose becomes a food for the bacteria living in intestines. The unpleasant symptoms of Fructose malabsorption often appear very similar to IBS or lactose intolerance. This condition is very common in patients experiencing symptoms of irritable bowel syndrome. Some experts believe that fifty percent of those with Irritable bowel syndrome (IBS) have fructose malabsorption. The symptoms present in fructose malabsorption are nausea, abdominal distention, vomiting, vitamin deficiencies, abdominal bloating, flatulence (sometimes excessive), diarrhea, constipation, fatigue, mental fog and stomach cramping and pain. It is fairly unknown among the medical community or even in mainstream literature. Fructose malabsorption is hard to find in health and medical books. Most doctors have no knowledge of its existence. It is estimated that thirty to forty percent of the population of Central Europe are fructmals. Individuals with fructose malabsorption are known as fructmals. Fructose is found widely in the diet as a free hexose, as the disaccharide, sucrose and in a polymerized form (fructans). Free fructose has limited absorption in the small intestine, with up to one half of the population unable to completely absorb a load of 25 g. Fructose is present in many of the foods we eat, usually in combination with glucose.