Fructose

Fructose (or levulose) is a simple sugar(monosaccharide) found in many foods and one of the three most important blood sugarsalong with glucoseand galactose. Honey; tree fruits; berries; melons; and some root vegetables, such as beets, sweet potatoes, parsnips and onions, contain fructose, usually in combination with sucroseand glucose. Fructose is also derived from the digestion of sucrose, a disaccharide consisting of glucose and fructose that is broken down by enzymesduring digestion.

Fructose is often recommended for, and consumed by, people with diabetes mellitusor hypoglycemia, because it has a very low Glycemic Index (GI32) relative to cane sugar(sucrose). However, this benefit is tempered by concern that fructose may have an adverse effect on plasma lipids. 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 effectsand glycationfor further informations.

Structure

Fructose, or levulose, is a levorotatorymonosaccharidewith the same empirical formula as glucose(C₆H₁₂O₆) but with a different structure. Pure fructose has a sweet taste similar to cane sugar, but with a "fruity" aroma. Although fructose is a hexose (6 carbon sugar), it generally exists as a 5-member hemiketal ring (a furanose).

The first -OH points the opposite way from the second and third -OH.

Isomerism

D-Fructose has the same configuration at its penultimate carbon as D-glyceraldehyde. Fructose is sweeter than glucose due to its stereomerism structure

alpha-D-Fructose

beta-D-Fructose

alpha-L-Fructose

beta-L-Fructose

Health effects

Fructose depends on glucose to carry it into the blood stream via GLUT-5 and then GLUT-2 (Buchs et al 1998). 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 diarrheadepending on the amounts eaten and other factors.

Fructose has by some been hypothesized to cause obesity(Elliott et al 2002), elevated LDL cholesteroland triglycerides, leading to metabolic syndrome. However, supplementation with fructose in the diet in human subjects has not led to increased obesity.

Fructose also chelatesminerals 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. However, it is considered approximately ten times more active (McPherson et al 1988) in the formation of glycationsthan glucose, so consumption should be limited in order to limit the consequent glycation-related damage to cellular and molecular function. This may be an important contribution to senescenceand many age-related chronic diseases (Levi & Werman 1998).

See also

• High fructose corn syrup
• Fructose intolerance
• Fructose malabsorption

References

• Buchs AE, Sasson S, Joost HG, Cerasi E. Characterization of GLUT5 domains responsible for fructose transport. Endocrinology 1998;139:827-31. Fulltext. PMID 9492009.
• Elliott SS, Keim NL, Stern JS, Teff K, Havel PJ. Fructose, weight gain, and the insulin resistance syndrome. Am J Clin Nutr 2002;76:911-22. Fulltext. PMID 12399260.
• Levi B, Werman MJ. Long-term fructose consumption accelerates glycation and several age-related variables in male rats. J Nutr 1998;128:1442-9. Fulltext. PMID 9732303.
• McPherson JD, Shilton BH, Walton DJ. Role of fructose in glycation and cross-linking of proteins. Biochemistry 1988;27:1901-7. PMID 3132203.
• Higdon, J., Linus Pauling Institute, Oregon State U. Chromium 2003th:???????

ca:Fructosa da:Fruktose de:Fruchtzucker et:Fruktoos es:Fructosa eo:Fruktozo fr:Fructose it:Fruttosio he:??????? lt:Fruktoz? lb:Fruktos nl:Fructose ja:?????? pl:Fruktoza pt:Frutose sv:Fruktos uk:???????? zh:??

See whole new Fructose problem [1]

For more details about fructose metabolism see: * Horn, R., [2]

This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Fructose Wikipedia article Fructose.