Saccharin (the stuff in pink packets):
Supposedly saccharin was found to be carcinogenic in lab rats, in particular causing bladder cancer, but harmless to humans because rats concentrate their urine a lot more than we do, but my professor says, 'so what if someday our kidneys decide to concentrate our urine more" (perhaps because of excessive salt intake)? So he doesn't touch this stuff.
Splenda (the new stuff in yellow packets):
Compare to sucrose, from which it is derived:
So Splenda (sucrolose) is sucrose with 3 OH groups replaced by Cl's. My professor says, in a very chemistry-professor sort of way, something like "Now see how easy it is to have a nucleophile attack and displace chloride, a good leaving group. I don't want this sort of thing happening in my body. I use 0 Splenda."
Nutrasweet (the stuff in blue packets):
Basically just a dipeptide formed with aspartic acid at the N-terminus and phenylalanine at the C-terminus. Now my chem professor, who drinks like 5 bottles of Diet Pepsi a day, insists that Nutrasweet is completely harmless since it can only be broken down into naturally occuring amino acids, and that drinking it is "just like eating steak." My neuroscience professor would beg to differ. Aspartic acid is structurally similar to glutamic acid, a neurotransmitter that, when present in excess, can be excitotoxic and cause neuron death. When taken orally, excessive intake of these two amino acids could kill neurons in areas of the brain not protected by the blood brain barrier, making the young particularly susceptible. So taking too much Nutrasweet is basically the same as having too much MSG. Now, drinking diet soda and eating out at Chinese restaurants once in a while probably won't really have enough of an effect, but if you drink a gallon of diet soda every day... I wonder if I should tell my chem professor that.
So the take-home lesson, I guess, is that all artifical sweeteners present some sort of health danger. And that synthetic chemicals are bad. Ha.