I ask Gemini health questions non stop and never see it using YouTube as a source. Quickly looking over some recent chats :

- chat 1 : 2 sources are NIH. the other isnt youtube.

- chat 2 : PNAS, PUBMED, Cochrane, Frontiers, and PUBMED again several more times.

- chat 3 : 4 random web sites ive never heard of, no youtube

- chat 4 : a few random web sites and NIH, no youtube