Fructose, like table sugar, is an energy-containing compound that has a sweet taste. Your cells can burn fructose to provide immediate energy, or store it for later use in the form of either glycogen, a carbohydrate stored in the liver and muscles, or fat. If you're looking for a substitute for fructose in your food, there are several options available to you -- some of them contain calories, and others do not.
While table sugar isn't a substitute for fructose, it actually contains fructose, you can use pure glucose to substitute for fructose. Unfortunately, both fructose and glucose contain identical numbers of calories per unit mass, but fructose is sweeter than glucose. This means, in general, you need to eat more calories worth of glucose to get the same sweetness you would from fewer calories worth of fructose. However, if you have fructose-induced digestive difficulties, as some individuals do, glucose may be a viable substitute. Sources of pure glucose include corn syrup and brown rice syrup.
Aspartame is a non-nutritive sweetener, meaning it contains no calories. Unlike glucose and fructose, aspartame isn't actually a sugar at all, explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry." Instead, aspartame, sold under the brand name Equal, is a modified protein that happens to bind to the sweetness receptor on the human tongue. You can use aspartame instead of fructose to provide sweetness to foods, though unlike fructose, because aspartame contains no calories, it has no nutritional value whatsoever. Furthermore, unlike fructose, aspartame isn't heat stable, meaning you can't use it in baking.
Another non-nutritive sweetener that you can use as a substitute for fructose is sucralose, often sold under the brand name Splenda. Sucralose is a modified sugar; it's very similar in chemical structure to table sugar, but has some chlorine atoms in it that table sugar doesn't have, in addition to a few other minor structural variations. The structural differences mean that you can't digest sucralose, because sugar-digesting enzymes are very structurally specific, explain Drs. Mary Campbell and Shawn Farrell in their book "Biochemistry." Sucralose, unlike aspartame, is heat-stable, so you can use it instead of fructose in baked goods and other cooked foods.