Sugar Substitutes & Sweeteners - Fructose

Fructose (or levulose) is a simple sugar (monosaccharide) found in many foods and one of the three most important blood sugars along with glucose and galactose. Honey; tree fruits; berries; melons; and some root vegetables, such as beets, sweet potatoes, parsnips and onions, contain fructose, usually in combination with sucrose and glucose. Fructose is also derived from the digestion of sucrose, a disaccharide consisting of glucose and fructose that is broken down by enzymes during digestion. Fructose is the sweetest naturally occurring sugar, estimated to be twice as sweet as sucrose.

Fructose is often recommended for, and consumed by, people with diabetes mellitus or hypoglycemia, because it has a very low Glycemic Index (GI 23) relative to cane sugar (sucrose). However, this benefit is tempered by concern that fructose may have an adverse effect on plasma lipid and uric acid levels, and the resulting higher blood levels of fructose can be damaging to proteins (see below). The low GI is due to the unique and lengthy metabolic pathway of fructose, which involves phosphorylation and a multi-step enzymatic process in the liver. See health effects and glycation for further information.

Health Effects
Fructose depends on glucose to carry it into the blood stream via GLUT-5 and then GLUT-2. Absorption of fructose without glucose present is very poor, and excess fructose is carried into the lower intestine where it provides nutrients for the existing flora, which produce gas. It may also cause water retention in the intestine. These effects may lead to bloating, excessive flatulence, loose stools, and even diarrhea depending on the amounts eaten and other factors.

Fructose has been hypothesized to cause obesity, elevated LDL cholesterol and triglycerides, leading to metabolic syndrome. Unlike animal experiments, some human experiments have failed to show a correlation between fructose consumption and obesity. Short term tests, lack of dietary control, and lack of a non-fructose consuming control group are all confounding factors in human experiments. However, there are now a number of reports showing correlation of fructose consumption to obesity, especially central obesity which is generally regarded as the most dangerous type. (Wylie-Rosett, 2004)(Havel, 2005)(Bray, 2004) (Dennison, 1997)

Fructose also chelates minerals in the blood. This effect is especially important with micronutrients such as copper, chromium and zinc. Since these solutes are normally present in small quantities, chelation of small numbers of ions may lead to deficiency diseases, immune system impairment and even insulin resistance, a component of type II diabetes (Higdon).

Fructose is a reducing sugar, as are all monosaccharides. The spontaneous addition of single sugar molecules to proteins, known as glycation, is a significant cause of damage in diabetics. Fructose appears to be as dangerous as glucose in this regard and so does not seem to be the answer for diabetes (McPherson et al, 1988) This may be an important contribution to senescence and many age-related chronic diseases (Levi & Werman 1998).

Fructose is used as a substitute for sucrose (common sugar) because it is less expensive and has little effect on measured blood glucose levels. While most carbohydrates have around the same amount of calories, fructose is sweeter, so manufacturers may use less fructose to get the same sweetness. It is lower cost and may have lower added calories, so it is being seen as a profitable sweetener. The free fructose present in fruits, their juice, and honey is responsible for the greater sweetness per amount of these natural sugar sources.

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