Fructose has gotten a bad rap, as far as sugars go. We know, as a general rule, that sugar isn't the best thing we could be putting into our body, but is fructose really as bad as it's been made out to be?
The body really works with two types of sugars: glucose and fructose. Glucose triggers the pancreas to pump insulin into the blood, storing it in the muscles and liver. It also helps suppress our hunger, with a little hormonal help from leptin. Fructose, on the other hand, does not bring out an insulin response and increases the blood levels of grehlin, a hormone that makes us hungry. This can cause overeating and weight gain.
When we eat too much fructose, we tend to produce more fat, and therefore more triglycerides hanging out in the blood. High triglycerides are the major risk factors and market for heart disease.
The liver converts fructose into energy. In fact, most of the fructose metabolism in our body rests on the liver's metaphorical shoulders. Therefore, eating a whole bunch of fructose, as is prominent in the Standard American Diet, is incredibly stressful on the liver. It's so worn out from taking care of all of the fructose that it doesn't have the energy to take care of its other detoxification function. A tired liver can cause gout, kidney stones, and high blood pressure, due to the production of uric acid.
Fructose is a double whammy on the liver, because excess consumption is linked to a fatty one. A fatty liver as well as increased levels of uric acid may contribute to insulin resistance, or the inability to regulate glucose levels. Obesity and type 2 diabetes go hand in hand with insulin resistance.
When fed a high-fructose diet, rats were less physically active, contributing to their weight gain.
However, we have to watch the amounts and types of fructose. Many of these studies use a primarily fructose (up to 300 grams) per day, while the average consumption of sugar is about 150 grams per day, often unaccompanied by glucose. Therefore, these studies may have unrealistic conclusions about the effect that fructose really has on the body.
Or... they may not be too far off. Let's look as where we're getting fructose. Fruit, for example, is packed with fructose, but it is structured to slow digestion and break down fructose before it even reaches the liver. On the other hand, a Coke will annihilate our liver with intact fructose. Three hundred grams of fructose is about eight cans of coke. I definitely know some people who can consume eight cans of Coke in one day.