In the first few months my goal each day was to be Sober, that was as much as I could deal with and so I ate what I craved, sugar, chocolate, an extra biscuit with a cup of tea, I had a sole focus and that was not to touch alcohol.
As time goes on though and Sobriety gets "easier", temptation fades and Sober muscles are developed, less of my time and energy was spent worrying or being consumed with thoughts of drinking and I was able to sort out my diet/exercise etc.
In my opinion at the start, do what you need to do to remain Sober, if that doesn't happen, then what's the point of being healthy in other areas of life? alcohol was going to kill me if I didn't get that bit right, all of that can wait until you have some Sober time under your belt!!