Some researchers claim the extraterrestrial underground bases are utilized also as warehouses for humans as a food source for Reptilians. Is this true?

This is true. There are multiple uses for the underground bases. They sequester alien craft in between missions to keep them safely protected and out of sight, house personnel so they have living space that will be unobservable from the air or ground, and are used as a holding area for abductees. There is also an ongoing need for food for Reptilian personnel. Because they are in charge, they indulge themselves in whatever way they wish, and they particularly relish human flesh, especially tormenting the victim to be eaten prior to the feast. This is an illustration of their advanced state of depravity, that they can treat a sentient being in such a fashion to delight in its torment knowing it is vulnerable and even about to be killed and consumed. So, unfortunately, the large number of bases needs to be stocked with provisions and that includes human beings as foodstuff, as a source of nutrition for the extraterrestrials.