I can also vouch that low (and high) blood sugar levels can cause mood swings! But also, as others have mentioned, your husband may be struggling with acceptance etc. Ask him (when he's not in one of his bad moods!) whether he thinks it's his blood sugar levels or whether it's deeper than that. Surely this will result in you getting an answer rather than just trying to guess what it is!
Good luck - this can be difficult to deal with sometimes, but then doesn't everyone have a problem or two.