I had gestational diabetes during my second pregnancy. I basically stopped eating fruit as it is high in fructose, which is a sugar. I also didn't eat much potato, white rice, cereals (except small amounts of whole grain), bread (only a couple of slices of burgen low GI bread a day), pasta (only a tiny amount of wholewheat) as the carbs are converted to sugars. If you do eat any of those, have very small amounts. I also cut back on yoghurt, even plain as well as milk as that's lactose which is a sugar, but I was careful to get calcium from other sources - tofu is a good one as are green leafy veg.
Most meals were very high protein, for example, 2 scrambled eggs on one piece of toast with a cooked tomato and a slice of bacon. This kept me full up until lunch/dinner. Or a whole wheat wrap with cheese, mayo and cucumber.. Evening meals were again high protein, with loads of veg and tiny portion of carbs.
If I did need something to snack on, I stuck to mixed nuts or peanut butter on a cracker.
I will say, it can be a bit of a shock to the system,and a lot of jthe process was trial and error for me. I went through horrible couple of weeks as I was in sugar withdrawal and was a hormonal, raging mess, but I also had other problems in pregnancy and wasn't coping well. I did lose weight though(a stone after 10 weeks), but I am very fat anyway so it was expected. Good luck curiousgeorgie 