Oh sugar!?

This post isn't really directly related, but rather something I've noticed over the last bit.

I'm in the middle of the Baha'i fast at the moment, and have been finding it easier to focus while playing.  Today I craved chocolate - so I had some.  While looking at chess tactics I'm finding it hard to focus.  It occurs to me that this lack of focus happens everytime I crave sugars.

Time to look at sugar substitutes.  Anyone got any ideas what would be worthwhile?