Well I think I had a bit of a Eureka moment - in one of his graphs he shows glucose levels going up in a little spike, before they start reducing dramatically and thing really start changing. I've seen this happen with my levels when I've tried intermittent/irregular fasts (I just don't eat when I don't feel hungry - usually over 12-18 hour periods) over a week or so and taken it as a sign that my body wasn't too happy about what I was doing so stopped before I was actually reaching the beneficial stage, as I've mainly been concerned about keeping my glucose levels down.
So next time I'll just keep on going, and see what happens. It's maybe a time when using a Freestyle sensor would be a useful tool.
Robbity