Archive for Sucrose

Fructose metabolism

Posted in Food, Health, Nature with tags , , , , , , , , , on 2012/06/12 by rmolby
High Fructose Corn Syrup

High Fructose Corn Syrup (Photo credit: Food Thinkers)

This post is part of my health research on my own weight and health problems. Part of fixing my health issues is learning how the human body processes or digests food and food-like substances; there is a single word describing this process: metabolism.

Anyway, in relation to the previous post, the first thing I was interested in is how the human metabolism deals with simple carbohydrates, like high fructose corn syrup (HFCS), honey, and sugar, etc/.

So the way I understand it, when we digest plain sugars, such as sucrose (white table sugar) or honey, they pass through the stomach almost unchanged and go into the small intestine where the enzyme sucrase splits the sugar into its glucose and fructose component.

HFCS on the other hand, being a man-made product, doesn’t have strong bonds between the glucose and fructose molecules, and can be broken down easily in the small intestine.

The now available glucose is absorbed by the intestine, and transported directly to the blood as energy source, and all excess glucose is sent to the liver to be processed into glycogen. At the same time that glucose level rise, so do insulin levels, when a certain threshold of glucose is reached the hormone ghrelin drops off, signaling to the brain to stop consuming carbohydrates.

Fructose on the other hand is also absorbed by the small intestine, but to a lesser extend and using a slightly different process, and very few tissues in the human body are able to utilize fructose. What fructose is not absorbed by the small intestine is sent on to the large intestine to be fermented there into hydrogen and carbon dioxide.

What fructose is absorbed by the small intestine is transported directly to the liver to be processed by fructokinase, using phosphate, and is further metabolized into different compounds.

The metabolism of fructose at this point can lead to glycogen synthesis as well as fatty acid and triglyceride synthesis. Glycogen is the first compound that is produced, once the liver has a sufficient level of glycogen, it will begin to produce triglycerides, and finally, fatty acids.

Hence, when we consume anything that contains fructose, whether it be honey, sugar or HFCS, our triglyceride and fatty acid levels rise.

The triglycerides are then incorporated into very low density lipoproteins (VLDL, the “bad” cholesterol), which are released from the liver for storage in both fat and muscle cells.

During the entire process of metabolizing fructose, the hormone ghrelin never goes down in level or intensity, so the brain does not get any indication to stop consuming carbohydrates, causing us to continue to consume carbs, which gives us more fructose, which causes more triglyceride and fatty acid, still not dropping ghrelin, and cycle continues.

So there we go, fructose makes us fat, and it doesn’t matter if it comes from HFCS, honey or sugar. So the generalization we hear, sugar is sugar appears to be reasonable after all. The only difference is that HFCS absorbs into the intestine faster than sugar or honey, because it does not have to be broken down into glucose and fructose by the enzymatic process.

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