Aspartame (Nutra Sweet) is 200 times sweeter than sugar. It has a caloric value similar to sugar, but the amounts used are small enough to consider aspartame essentially free of calories. It is not for use in cooking or baking as heat breaks it down into free amino acids. It should not be used by individuals who have phenylketonuria (PKU). (PKU is a genetic disorder in which the body can't process part of a protein called phenylalanine (Phe). Phe is in almost all foods. If the Phe level gets too high, it can damage the brain and cause severe mental retardation.)

Saccharin (Sweet 'n Low) is 200 to 700 times sweeter than sugar and has no calories. Some people complain that it has a metallic, bitter taste.

Sucralose (Splenda) is 600 times sweeter than sugar and has no calories. It is popular, in part, because it may be used in cooking.

Olestra (Olean) has properties similar to those of a naturally occurring fat. But, unlike the natural products, this synthetic fat substitute provides no calories or saturated fat because it is indigestible: It passes through the digestive tract but is not absorbed into the body.

For more information, see:

http://www.fda.gov/fdac/features/2006/406_sweeteners.html

http://www.cfsan.fda.gov/~dms/bgolestr.html