Recent European research suggests that ingesting aspartame leads to the accumulation of formaldehyde in the brain, other organs and tissues (Formaldehyde has been shown to damage the nervous system, immune system, and cause irreversible genetic damage in humans.)
An extremely large number of toxicity reactions have been reported to the FDA in the US and other organizations
A recent report showing that nearly 100% of independent research has found problems with aspartame.
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Aspartame
Splenda is Sucralose which is a dirivitive of sugar. It is produced through a chlorination process which some would say is not natural but not shown to be harmful in any way. Certainly not in the way that other sweeteners are now being questioned. It just took a long time for the UK food authorities to approve it.
You can cook with it in spoonable form or it is available in tablets.
All sweetners have a filler as the active ingredient is ultra sweet. In the case of Splenda it is Maltodextrin. Splenda was I understand developed by Tate & Lyle here in the UK.
The general problem with Sweetners, including Splenda is that they mimick the effect of carbohydrate and can stimulate insulin production and do nothing to wean one off the sweet craving. For this reason Atkins on induction suggests no sweetners either.
If you are looking for the best tasting and the least harmful sweetener then it has to be Splenda. The food industry in this country is beginning to change to Splenda. It was available to them before the table product became available to us a few months ago.