I think its not possible to get black hair back once they goes greyMod. Edit. Posts moved from another thread.
Absolutely right! Here's something for folks to chew on. I was a vegetarian for 20 years starting in my early teens. I started going gray at the age of 19. By my 30s my hair was almost 90% gray. Three months ago I started low carb high fat and my hair is returning to brown in several areas. My hairdresser was BLOWN AWAY! She said she didn't even need to color my hair in the back anymore. I attribute it to all of the fat and animal proteins. I just hope any damage I did to my body being a low fat vegetarian for 20 years is reversible. I guess if my hair is reversing other stuff will too.
EDIT to add: I quit being a vegetarian about 7 years ago but was still eating high carb. My hair didn't reverse then. So it's something about the low carb high fat diet that is returning my hair to normal.