The koins do not need food, they feed on the energy that happy living beings emanate. However, they love earth food, especially fruits and vegetables. They also have a sweet tooth!
When a Training Tank is at the right level, it is possible to treat the koins housed there to Snacks.
Snacks can be purchased with utility token and when consumed, they improve our Empathy Value with the koin in question. There are several types of Snacks to pamper your koins!