What about Fructose?
Glad you asked. Fructose, found mostly in fruits and some root vegetables, is processed differently than glucose. Instead of entering your bloodstream and triggering an insulin response, fructose heads directly to your liver for processing. This is why carbohydrates with a higher percentage of its sugars in the form of fructose will naturally have a lower glycemic value. Simply put, your blood glucose levels cannot be increased if you are consuming fructose instead. This is one of many reasons why the glycemic index is of very little value.
As the liver processes fructose, multiple elements of heart disease become elevated. That is, triglyceride levels are increased and LDL particles are oxidized. The sad thing is, cholesterol gets blamed as being at fault when it is the fructose consumption that is turning the cholesterol into something harmful.
The elevated level of triglycerides also impairs the transport of leptin into your brain. Fructose is unable to enter the cells of your brain (think wrong key/lock combination). If leptin does not reach your brain, your brain will not send out the signal to stop eating. This means that fructose does not have the same satiety effect compared to that of glucose.
At the same time, the amount of leptin secreted has already been decreased because of the smaller insulin response produced by your consumption of fructose. It is the secretion of insulin which triggers leptin secretion in the first place.
Leptin is not the only hormone responsible for hunger. Ghrelin, produced in the stomach, signals hunger. Contrary to leptin, ghrelin increases before meals and decreases after meals. Fructose however does not suppress ghrelin levels as much as glucose does.
As if obesity and heart disease weren’t bad enough, fructose consumption also increases uric acid levels in the body, which in turn results in gout. Again, fructose somehow escapes all blame though and gout sufferers are instead told to refrain from red meat.
Your liver itself isn’t safe either. Having to process excessive amounts of fructose can actually lead to fatty liver disease. That’s right, your liver will look identical to that of an alcoholic if you eat enough fructose.
Not all of the fructose makes its way to your liver though. This is a problem because it is significantly more reactive in the bloodstream than glucose. In fact, fructose is 10 times more effective than glucose at inducing the cross-linking of proteins that leads to advanced glycation end-products (AGEs). AGEs are toxic and contribute to such things as atherosclerosis, asthma, arthritis, myocardial infarction, nephropathy, retinopathy, and neuropathy. These AGEs are also more resistant to the body’s disposal mechanisms than those created by glucose.
Stay tuned for part 4 where we will discuss sucrose and high-fructose corn syrup.