They might attach "Nutrient paste" to their mouthpieces.
They probably have a reservoir in their suit for such things. Kinda like how a person can drink water from a canteen while wearing a gas mask, same principle really. Esparc For all we know, the mouthpiece on their mask could also provide a small opening for them to eat, besides if they eat "nutrient paste", it probably would be on the tubes we have seen with drinks.
Emergency induction port. 188.8.131.52
^ That's a straw, Anon. RShepard227
- Blast! Someone beat me to the "Induction Port" pun... it's mentioned that the quarians tend to eat in turian shelters or clean environments that they can remove their suits in if away from the flotilla. On the flotilla they create a vegan paste for everyone that could easily be piped through the suit into a straw similar to the camelback water bottles a hiker uses. Tali also mentions the ability to seal off sections of the suit like bulkheads on ships. I'm not sure how effective it would be to seal off from the neck down in order to remove the mask to eat, but if done in a clean environment it would probably work. KaedAemoh
According to the codex about liveships, it is through feeding tubes.