Fructose is mostly known as the sugar inside the fruits, but it is not exactly true. The sugar inside the fruits is called levulose, which is a fructose, bounded by different minerals, vitamin, fibre and other different stuff. The fructose sugar is just one part of it.
The fructose, that is normal added to the products, is refined, going through numerous chemical processes, to become the single molecule on the end. I would rank it about the same as margarine in terms of how processed it is.
We, as the normal consumers, do not really know, what is happening with the food during all the processing stuff. What do they add? What chemicals do they mix in? What temperature do the use? How long does it take?
On the other hand, the levulose is made by plants, that use the sun and the minerals in the ground to create the piece of fruit. It needs days, sometimes months, for the process to finish, and after that, the only thing left to do is to eat it. Do does not like the sweet taste of the fruit?
But there are also differences inside our bodies, once the two ingredients enter our digestion system.
The levulose is digested in the bowel track, with most of the other natural food. On the other side, fructose is digested in the liver.
That can have one positive effect. Since it is digested in the liver, it does not cause the spike in the blood sugar, like most of the other sugary substances, making them safer for diabetics. Or at least that is what they are trying to tell you.
But being digested inside the liver means, that it gets transformed into the body storage almost immediately. First there are sugar reserves inside the liver, but if they are full, the remainder is going to be transformed into a body fat.
Also, the fructose inhibits the feeling of fullness. By stopping the normal functioning of the enzyme named leptin, you could continue to eat and eat, but the feeling of fullness would not come. Some studies indicate it could have a reverse effect. The more it is consumed, the more the body gives signals for more food.
There are also some indications, that consuming fructose on the long run can hurt liver, mineral balance,...
Our bodies are more complex, than just one substance could have an effect on the body. But give it in too much quantities, or consume some other similar acting substances, and the end result could be obesity, or even something worse.