Bone lost during rapid starvation or extreme weight loss in midlife cannot be regrown or reversed.
"You're going to absolutely lose bone. And this is not stuff you can reverse, by the way. You don't lose bone and grow it back. It doesn't work that way." (said at 0:11:59)
No published record matching the claim that bone lost during weight loss or starvation in midlife cannot be regrown or reversed was located; this does not prove the claim false.