User blog comment:Kaido King of the Beasts/Chapter 867: Suns and Daughters/@comment-30127592-20170601163429/@comment-30127592-20170601224126

that's a good question, and if I remember correctly Oda never showed whitebeard's body after blackbeard finished extracting the Goru Goru no mi, so any further information from his death is unobtainable. His body was still buried, so any missing body parts would definitely be noticed, but it's possible those were attributed to the damage he sustained during the war. That would still imply that, should blackbeard use cannibalism as his harvesting method, it's a rather small body part, likely a single organ e.g. the heart, that "holds" the power.