Sugar substitutes can be made from natural or synthetic products. These synthetic versions are called artificial sweeteners.Its best to avoid taking artificial sweeteners like aspartame, saccharin etc .
Aspartame is made from two amino acids; aspartic acid and phenylalanine. Saccharin is made from the reaction between sulfur dioxide, chlorine, ammonia, and two biochemical acids. There are some natural sweeteners made from sugar but to make them zero calories they are mixed with chlorine. It is then called Sucralose. This is better than the previous two. But try to avoid all artificial sweeteners.
Diet Coke, Diet Pepsi and these days some imported sweets and chocolates are also made from these products and for marketing reasons are advertised as Fat Free, Diet, or Zero Calories etc. They all will do more harm than good for your body.
Sugar substitutes don't make you lose weight, in fact you will be surprised to know that it actually helps you to gain weight because of the way these chemical compounds break and get absorbed in your body to digest.
They may have lesser or no calories which is very true but are best to be avoided due to the various illnesses related to its usage that researchers are proving recently .
Aspartame has many and very bad side effects which could either develop suddenly or slowly and it can cause serious damage to the nerves of the eye, ear and other neurological damages also resulting in depression, insomnia, irritability etc.
Although that there is no proof that it leads to cancer, researchers are relating that the use of aspartame may lead you into such life taking diseases.
Its best to use natural sugar in a lesser quantity than trying the artificial sweeteners.