Different foods affect the body in different ways and sugar is uniquely fattening. Sugar (sucrose) and high fructose corn syrup contain two molecules: glucose and fructose.
Glucose is absolutely vital to life and is an integral part of our metabolism. Our bodies produce it and we have a constant reservoir of it in the bloodstream. Every cell in the body can use glucose for energy. If we don’t get glucose from the diet, our bodies produce what we need out of proteins and fats.
Fructose, however, is very different. This molecule is not a natural part of metabolism and humans do not produce it. In fact, very few cells in the body can make use of it except liver cells. When we eat a lot of sugar, most of the fructose gets metabolized by the liver. There it gets turned into fat, which is then secreted into the blood.
Fructose Causes Insulin Resistance. Have you ever heard of the hormone Insulin? It is one of the key hormones that regulate human metabolism and energy use. Insulin is secreted by the pancreas, then travels in the blood to peripheral cells like muscle cells.
Insulin sends a signal to these cells that they should put transporters for glucose onto their surface, thereby allowing glucose to get into the cells where it can be used. When we eat a high carb meal, glucose levels go up. Excess glucose is toxic so insulin rapidly goes up in order to get the glucose out of the bloodstream and into the cells.
If we didn’t have insulin or it wasn’t functioning correctly, blood glucose would reach toxic levels. In healthy people, this mechanism works very well and enables us to eat meals that are high in carbohydrates without our blood glucose going out of whack.
However this mechanism tends to break. Cells become resistant to the effects of insulin, which makes the pancreas have to secrete even more to drive the glucose into the cells. Basically, when you become insulin resistant, you will have more insulin in your blood all the time (until the entire thing breaks and leads to type II diabetes… which can happen eventually). But insulin also has other functions. One of them is sending signals to our fat cells. Insulin tells the fat cells to pick up fat from the bloodstream, store it and to avoid burning the fat that they already carry.
When insulin levels are chronically elevated, much of the energy in our bloodstream gets selectively deposited in the fat cells and stored. Excess fructose consumption is a known cause of insulin resistance and elevated insulin levels in the blood. When this happens, the body has a hard time accessing the stored fat and the brain starts to think that it is hungry. Then we eat more.