If you inflated too much, you'll lose a life.
Additional information here. 'Spoilers though'
1. Normal bullets can't kill you in this mode, it inflates you. Dangerous than cake pieces of course.
2. Boss fight: usually if you lose on most modes, you can't gain back. But in this mode, you lose, and you'll gain back inflated. So you better win. In addition, you can't lose the carbs which you gained during boss fight.
3. Fully inflated doesn't give you an ability. No distant helpers, no burst bang, nothing. But special ability like 'bubblegum' does 'do the trick'. Even to the boss. Unfortunately, 'fully inflated' related skills still lose life.
So, the best option is blueberry and antimatter. Or you could use 'molded' in someway to not eat usual cake pieces (Not recommended cause of the gas meter hard to parry).
P.S. Although I tell these information, try to find out and experience yourself to enjoy the game. For you and the developer. ^^