Well, I'm no expert, and your comments are perfectly valid, but I'm not sure that premise (A): The quantities of aspartame ingested by rats in the studies finding deleterious effects far exceed, on a relative basis, what any sane human would consume; leads to conclusion (B): Aspartame is perfectly safe for humans. At best, your point tends to support an argument that those studies don't prove much of any practical value. I'm not expert either, but, it seems to me that giving a rat anything far in excess of what would normally be consumed would lead to problems. If you gave the rat regular table sugar in the amounts that those studies have fed aspartame to rats then there would be problems. The FDA, based on extensive studies conducted by the FDA and other medical bodies throughout the world, has said that it's safe for the average person to consume up to 50 miligrams of aspartame per kilogram of bodyweight. So, for example, say I weigh about 85 kilograms, I can safely ingest 4250 milligrams of aspartame. One diet soda has about 225 milligrams, so I can drink about 19 cans of diet soda per day before I reach dangerous levels. The reason I brought up the rat experiments is that those are the experiments that are most cited when people argue that aspartame is not safe, not because those experiments prove that aspartame is safe. There are numerous studies conducted by governmental and non-govermental researches that conclude that aspartame, in the amounts that are normally consumed by humans (because just about nobody drinks more than 19 cans of soda in a day), are perfectly safe. I brought up the rat experiments just to let people know that the reason that the rats in those experiments suffered negative effects (including IIRC cancer and brain damage) is because those rats were ingested with levels that FAR exceed what any human would ingest (not just exceed by a little, but exceed by a little - many times the amount that has been determined to be safe).