Answer: The words "sugar" and "sweetness" do not mean the same thing.
The sensation of sweetness occurs when a certain kind of receptor is triggered in your taste-buds. When that happens, a nerve signal is sent to the brain, and the brain interprets this to mean that there is something sweet in the mouth.
Sugars are the most common naturally occurring triggers for these receptors. There are many different kinds of sugar, but the most common one that you buy in the grocery store is called Dextrose. When sugar is broken down by the body, chemical energy is released. It can either be used to power ongoing activity, or it can be stored as fat if there is more than enough energy available at the time the food is being digested.
There are other chemicals which are not sugars, that can still trigger the sweet receptors. Saccharin is one of the chemicals which can do this. Saccharin happens to be a much more potent trigger for the sweet receptors than most sugars.
From the standpoint of a person who is trying to lose weight, saccharin is useful because it is able to give the sensation of sweetness, but it is not broken down by the body into anything that can be used as energy. Saccharin is mostly removed out of the body in the urine without being metabolized.
Answer: If you want to get really specific it would depend on where the person lives and their diet. An average person can have anywhere from 22 grams to 66 grams of sugar a day (or even more than that depending on their diet). So if they ingested 66 grams a day then overall they would eat 24,090 grams of sugar a year.