What a tadpole will eat depends on the species of tadpole as their diets vary.
Majority of tadpoles are inclined to eat algae and micro plants though. There are certain species of tadpoles that are actually omnivores and they will eat organic debris from animals and decomposed plants.
For ones that are kept in captivity they will eat such foods as egg yolk, baby food and lettuce.
Some often popular foods that people like to give to their pet tadpoles are spinach and lettuce.
Interestingly enough before a tadpole hatches it will eat its own yolk sack. When they are only a few days old their gills will start to develop and at this point they will become vegetarians.
However once their back legs develop they change their diet and become carnivores.
At this point they will eat larvae, insects and other small insects or small animals found in the water. And if there is not enough meat to be found in their habitat they will eat other tadpoles.