Hi Sally, it's this 600 cal (technically 800 cal) a day diet that has been shown to improve control in type 2 diabetics. It's been on the news quite a lot recently and there are a lot of posts about it on this forum.
In a nutshell, you have 600 calories worth of a supplement drink (optifast, I believe) every day. You then have a further 200 calories of starchy veg.
It's supposed to be very good for losing weight (not suprising when you eat so little!). I've heard a lot on this forum from type 2s who has tried it, but no type 1s...
Em