I think a lot has to do with the microflora one has. The microflora can absolutely be influenced by diet but part is simply unique to the specific person. The specific bacteria one is exposed to at birth has a huge impact for the rest of your life as your immune system tends to attack bacteria that you didn’t have in your first weeks of life. Taking antibiotics can also permanently alter the micro flora. I know more than one family where one specific member has horrific farts but the others don’t despite basically identical diet. So it really can just be bad luck. Not everyone drinking protein shakes gets horrific farts but some do.

Fart joke my cousin told me many years ago:

A guy goes to pick up a girl for a date. She’s not ready yet, so he sits down in the living room, where her dad is reading the newspaper. Their dog wanders in and settles down by the guy’s feet. Suddenly he has a powerful need to fart, but he’s afraid to do it with her dad in the room. He leans to one side and lets just a little bit escape, as cautiously as he can, but it makes a small noise. The dad leans out from behind his newspaper and says, “Duke!” The dog looks up sheepishly.

The guy is like, “Alright! He thinks it’s the dog!” He leans the other way and lets out a bit more; this one’s a little louder. Again the dad looks around the paper and says, “Duke!”

Figuring he’s completely safe now, the guy relaxes and lets out the rest in one big loud blast. The dad puts down the paper and says, “Duke! Get away from there before he shits all over you!”