Fructose, also known as levorose, is a naturally occurring simple sugar found in fruits and honey. It is twice as sweet as table sugar and has a low glycemic index, making it a natural alternative to table sugar for people who want to cut calories or maintain healthy blood sugar levels. For these reasons, it is sometimes used to make cakes, cookies and other sweets. However, care must be taken when using fruit sugar in home cooking as it has different physical and chemical properties from table sugar and cannot always be replaced in the same quantities in standard recipes.
Monosaccharides are the simplest form of sugar, each made up of a single sugar molecule. There are many monosaccharides, both synthetic and natural, but the only monosaccharides found in foods are fructose, glucose, and galactose. Monosaccharides are usually bonded in pairs, in which case they become disaccharides -- such as sucrose, maltose, and lactose. Sugar molecules can also bind to long chains called polysaccharides or complex carbohydrates. From a nutritional point of view, complex carbohydrates can be considered the most important form of sugar in the diet because they take longer to break down in the digestive system and produce more stable blood sugar levels than rapidly processed simple sugars.
The chemical formula of monosaccharides generally includes some multiples of CH2O. In a typical monosaccharide, the carbon atoms form a chain in which each carbon atom but one is attached to a hydroxyl group. The unbonded carbon forms a double bond with the oxygen molecule to form a carbonyl group. The position of the carbonyl group subdivides monosaccharides into ketoses and aldoses. A laboratory test called the Seliwanoff test chemically determines whether a particular sugar is a ketose (if sugar) or an aldose (such as glucose or galactose).
While fruit sugar and honey are generally considered safe, excessive consumption can lead to hyperuricemia, a condition in which uric acid levels rise in the blood. There are also digestive disorders associated with difficulty digesting or absorbing fruit sugars from the diet. Fructose malabsorption is a lack of the ability of the small intestine to absorb this particular sugar, resulting in a high concentration of sugar in the digestive system. The symptoms and detection of this condition are similar to lactose intolerance, and treatment usually involves removing the food that triggers lactose intolerance from the diet.
A more serious condition is hereditary fructose intolerance (HFI), a genetic disorder that involves a deficiency of liver enzymes needed for fructose digestion. Symptoms usually include severe gastrointestinal discomfort, dehydration, convulsions and sweating. If left untreated, HFI can cause permanent liver and kidney damage and even death. Although HFI is much more serious than fructose malabsorption, treatment is similar and care is usually taken to avoid any food containing fruit fructose or its derivatives.
