The method and sample adopted were feeding 1,900 rats with artificial sweetener in feed until they died. Thereafter rats were examined to see if they suffered from any disease.
The results of the study revealed that rats on aspartame-sweetened soda developed a variety of cancers. Thereby, establishing aspartame as a carcinogenic.
Previous US studies only observed the study animals to an age equivalent to 53 years old in humans. That is why previous studies would not find any evidence of the carcinogenicity of aspartame.