I should add another theory thats also getting popular due to the latest revelation of Blackbeard cant sleep.
Recent popular theory:
This theory says that Blackbeard is from snow islands and suffers from Central hypoventilation syndrome (CHS), which is also known as Ondine's curse.
CHP is a respiratory disorder that causes ineffective breathing, apnea, or respiratory arrest during sleep
https://en.wikipedia.org/wiki/Central_hypoventilation_syndrome
One of the main symptom of CHP is the inability to sleep.
In chapter 134, Luffy said that people from snow island dont sleep. If they sleep, they will die
Thats why this theory speculates the Blackbeard is from snow island. This theory also speculates Blackbeard attacked Drum island to kidnap doctors to treat him.
Its a nice piece of theory and makes a lot of sense, but doesnt explain how he consumed two fruits
Thanks, not my theory though.
Recent popular theory:
This theory says that Blackbeard is from snow islands and suffers from Central hypoventilation syndrome (CHS), which is also known as Ondine's curse.
CHP is a respiratory disorder that causes ineffective breathing, apnea, or respiratory arrest during sleep
https://en.wikipedia.org/wiki/Central_hypoventilation_syndrome
One of the main symptom of CHP is the inability to sleep.
In chapter 134, Luffy said that people from snow island dont sleep. If they sleep, they will die

Its a nice piece of theory and makes a lot of sense, but doesnt explain how he consumed two fruits
Thanks, not my theory though.
So they kinda tend to get things like hypoxia (low O2), hypercapnia (high Co2) -- typical of hypoventilation, as well as breathing-related symptoms... and are heavily dependent on mechanical ventilators to survive (and actually be able to sleep)... Can't remember the details exactly, but yeah... I remember reading this in Boron's Physio -- (I think chapter 33 or 34, iirc?? not sure)..
Personally tho', I think there's more to Blackbeard's sleep negligence than just him having a disease that forces him to stay awake.. and CHP is well... a thing no-one would expect to see in a children's manga (unless it's Blackjack)... but still, it's a nice theory, and I didn't notice that Luffy/Sanji convo... I mean, nice catch!!