Sunday, July 13, 2008

Fructose--Not as healthy as it appears to be

What if there was a food that could easily be converted to fat in your body? You would think that that food would be on the list of substances to avoid among those who are weight-conscious. You would be wrong.

Fructose is the sugar is found in most fruits. Like glucose, it is a simple sugar, but our bodies handle fructose in a special way. Look at the diagram below, which appears in Fructose, weight gain, and the insulin resistance syndrome by Sharon Elliot and coauthors.

The metabolic pathways for glucose are on the right side of the diagram. Note that there are many steps between glucose and the final product in this figure--acyl glycerols (triglycerides) which are packaged into VLDL (Very Low Density Lipoproteins) and sent out into the body for storage as fat. Depending on the body's needs, glucose can be used for energy via glycolysis and the citric acid cycle, and it can be stored as glycogen. If glucose is present in excess, it can be converted to triglycerides in the liver, but that is only one of many options.

For fructose, there are fewer choices. Fructose by itself does not stimulate insulin release. If insulin is low and glucagon is high, fructose can enter the gluconeogenesis pathway and be turned into glucose. But we seldom eat pure fructose. If we eat fructose with other carbohydrates, or if we eat it in the form of table sugar, the more likely situation is that insulin will be high and glucagon will be low. This will direct the fructose to be converted into the intermediates for fatty acid synthesis, and then into triglycerides. The result will be a phenomenon called fructose-induced lipogenesis.

Photo of apples:

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