Aspartame
A little bit on artificial sweeteners:
Aspartame is commonly recognized as Equal or Nutrisweet (blue packets). It is a synthesized chemical and a large amount of the population is intolerant to it (with all the symptoms listed about).
Sucralose is commonly recognized as Splenda (yellow packets). It is a derived compound made by chlorinating sucrose (sugar). Less people are intolerant to it, and those that are usually have trouble concentrating and gastro-intestinal distress (gas, diarrhea, constipation).
Saccharin is commonly recognized as Sweet'n Low (pink packets). It is a derived compound made from Toluene (a Coal Tar derivative used in paint-thinners). It has a pronounced after-taste, is linked to increased cancer risk. Most people have no tolerance issues.
I personally am intolerant to aspartame and sucralose... they give me wicked mean headaches and I can't concentrate. I am also intolerant of many of the other sugar alcohols used as sweetners in "diet" foods (mannitol, maltitol, sorbitol, etc.). Most of these give me serious GI distress - and that's pretty common, although most people have to consume a significant quantity before it affects them. But if you're eating diet food (like Nutrisystem) and are experiencing lots of gas... this could be the culprit.
The only non-sugar sweeteners I've found that I can tolerate are Stevia (although it tastes kinda funny), Saccharin (even though I try to avoid it), Acesulfame Potassium (Sunett or Sweet One), and Xylitol. Now Xylitol will give me some GI distress if I totally overdo it... but it also has the added benefit of making your teeth stronger (the only gum & mints my dentist recommends are sweetened only with Xylitol).
If you're intolerant to artifical sweeteners like I am, you may find that you'll have to "give up" many of your most coveted foods after surgery because the substitutes contain sweeteners that you can't handle. This is also true of many of the protein shakes and bars... so READ THE LABELS or you might be in for an experience almost as bad as dumping.