If you drink diet soda, you've surely encountered someone who says they heard that artificial sweeteners cause cancer. This has been a suspicion since the 1970s, when tests were performed on lab rats. The rats were exposed to high levels of saccharin, which were shown to cause bladder cancer, so saccharin was slapped with a warning label. Further research showed that rats have a predisposition to bladder cancer and the way saccharin affects rats doesn't apply to people because of our different physiology. So, the warning label was removed, but the bad reputation stuck.
Artificial sweeteners fall into the food additives category, so they're regulated by the FDA. This means they have to be thoroughly tested to be deemed safe before they become available in the marketplace. And over the years, no tests have conclusively proven that artificial sweeteners cause cancer. As part of the testing, the FDA has established an acceptable daily intake (ADI) for each sweetener. This number is around 100 times less than the smallest amount that could cause harm. You would have to drink diet sodas back to back all day long to get anywhere close to the ADI. So overall, experts say artificial sweeteners are safe for most people.
That isn't to say that some sweeteners don't cause complications for certain folks. People with the genetic disorder PKU (pheylketonuria) shouldn't use anything containing aspartame because they can't metabolize the main ingredient. And as we mentioned previously, sucralose can cause digestive difficulties for some people. For the rest of us, the rule of thumb with artificial sweeteners is the same as with most other foods. Moderation is the key.