John the Baptist

I hate it when, the night before your exam, you are reviewing your lecture notes and you find something written in your own handwriting that is patently ridiculous. In my endocrine notes I just found the sentence:

"Growth hormone is like John the Baptist".

Now I didn't make that up, I remember the lecturer saying it, and I remember me writing it down because I thought it was very clever.

But what on earth does it mean??