Fructose is a naturally occurring sugar found in many foods, mostly fruit. Fructose can also be found in processed foods and beverages as a sweetener. When multiple fructose molecules are linked in a chain (ending with a single glucose molecule) this chain is called a "fructan". Fructans are found in many vegetables and grains, such as onions and wheat.
Fructose Malabsorption Disorder is the inability to absorb fructose and fructans. This condition is NOT characterized by the inability to "tolerate" fructose/fructans. Sufferers of Fructose Malabsorption (or "FructMal" as it is commonly known amongst many sufferers) have no difficulty tolerating fructose/fructans once they have been absorbed. However, inducing absorption is difficult or impossible for FructMal sufferers. The symptoms of the disease are the result of having unabsorbed fructose/fructans in the lower intestine.
Fructose Malabsorption Disorder was formerly known as Dietary Fructose Intolerance. This term is being abandoned due to medical inaccuracy and potential confusion. Inaccuracy because, as mentioned above, FructMal is not a difficulty with "tolerance". Confusion because there is another condition, Hereditary Fructose Intolerance, which is a tolerance condition and is a serious genetic malady which can result in liver damage and even death. Fructose Malabsorption Disorder and Hereditary Fructose Intolerance should not be confused with one another. They are very different conditions with very different treatments.
The symptoms of FructMal are two-fold. The initial symptoms are gastro-intestinal and usually manifest within a few hours of ingestion and can last up to several days. When a FructMal sufferer consumes a food containing fructose or fructans, the unabsorbed fructose travels down to the lower intestine. The intestinal bacteria then voraciously metabolise the fructose, creating hydrogen gas (some individuals have intestinal bacteria which produce methane, or a combination of hydrogen and methane). This results in cramps, bloating, gas, and osmotic diarrhea. ***NOTE: in some people, FructMal causes constipation rather than diarrhea. This is rarely mentioned in literature, but if you suffer from constipation, don't assume you're not FructMal if the rest of the pieces fit.
The secondary symptoms manifest within a few days of ingestion and also last for several days. Fructose in the lower intestine will bond with any tryptophan present, making it impossible for the sufferer's body to absorb this essential amino acid. As tryptophan is utilised by the body to create both melotonin (to aid in sleep) and serotonin (to aid in positive mood), the reduction of tryptophan absorption inevitably leads to low levels of these neurotransmitters in the blood. Low levels of these neurotransmitters are associated with depression, anxiety, anger, lack of focus and inconsistant sleep patterns.
You cannot be sure you have Fructose Malabsorption Disorder until you have been formally diagnosed by a medical professional. This is done with a Breath Test. Usually a Hydrogen Breath Test will detect it, but as some individuals have intestinal bacteria that generate methane, a Methane Breath Test should be done if the Hydrogen Breath Test is negative.
The Absorption Process:
This is a great article on how different sugars (including fructose) are actually absorbed into the blood stream. Of particular interest is the bottom segment, "The Transport Mechanism"
created by A. Thompson 2008