Answer:
Caffeine.
Step-by-step explanation:
The independent variable for this experiment is the amount of caffeine because there is no effect on the caffeine in the experiment while on the other hand, weight loss is dependent variable which affects due to the amount of caffeine. Independent variable are those which can't depend on any variable in the experiment and can stay independently. There is no effect on the amount of caffeine so we can say that it is an independent variable.