I do not see how cutting out all sugar would help bipolar. Anecdotally - and only anecdotally - keeping blood sugar level does help, but to keep blood sugar level it is enough to consume protein and/or fat together with carbohydrates - you do not need to cut out all sugar. Just limit carbohydrates and do not eat sugar or drink sugary drinks in isolation. Only the glycemic index of the whole meal, or snack, matters - if individual foods/drinks with a high GI are balanced out by foods with a low GI, you should be OK. And it is much more doable and realistic in the long run than cutting out all sugar (fruit contains a lot of natural sugar and you do not want to cut out fruit).