Answer:
this effect has only been demonstrated in model animals (in this case rats) and therefore the outcome of this research cannot be generally extended to humans
Step-by-step explanation:
In the last centuries, experimental animals have been extensively used as research models in order to assess the possible outcomes in humans. In this regard, it is important to highlight that almost all medical development in use today (e.g., vaccines, medical drugs, therapies, etc) were first developed and tested in animal models before being used in humans. However, animal models are not humans. In this case, rats obviously don't have the same metabolic pathways (and food habits) as humans, thereby results cannot be translated directly to humans. In consequence, this study might be considered as a proof of concept, but further research is needed to determine the effects that drinking diet soda may have on human weight.