Pre-Approval Research. Pre-approval research showed that sucralose caused shrunken thymus glands (up to 40% shrinkage) and enlarged liver and kidneys. The manufacturer put forth two arguments in an attempt to claim that sucralose is not toxic:
The dose of sucralose in the experiments was high. However, for chemicals that do not have generations of safe use, the dosage tested must be adjusted for variations in potential toxicity within the human population and between humans and rodents. In order to this, toxicologists estimate a variation of effects in the human population of 10 times. In other words, one person may not have effects until a dose of 10 mg per kg of body weight (10 mg/kg) is reached, while another person may have chronic toxicity effects at 1 mg per kg of body weight (1 mg/kg). In addition, it is well known that many chemicals are much more toxic in humans than in rodents (or even monkeys). For example, the chemicals that the sweetener aspartame breaks down into vary from 5 to 50 times more toxic in humans than in rodents. Therefore, toxicologists estimate a further 10 times the dose for differences between human and rodent toxicity for a total of 100 times (10 * 10).
In order to estimate a potential safe dose in humans, one must divide the lowest dose in given to rodents that was seen to have any negative effects on their thymus glands, liver or kidneys by 100. That dose is then known as the maximum Tolerable Daily Intake (TDI) for lifetime use. Keep in mind that the TDI is just an estimate. Some chemicals are much more than 10 times more toxic in humans than in rodents (or will cause cancer in humans in low-dose, long-term exposure and do not cause cancer in rodents at all). A person ingesting the TDI for some chemical may find that it causes cancer or immune system or neurological problems after many years or decades of use. So, if the manufacturer claims that the dose was equivalent to 50 diet sodas, then the TDI would be one half (1/2) of a diet soda, and even that dose may or may not be safe
The manufacturer claimed that the sucralose was unpleasant for the rodents to eat in large doses. They said that starvation caused the shrunken thymus glands. From the New Scientist (23 Nov 1991, pg 13):