From what I've read I don't think so, it's about the calories and the feeling of hunger that has good effects on health and weight loss. The only downside of having sugar would be not being able to each much in terms of quantity. Hope that helps x
I don't think sugar would be the *best* thing you could eat on your fast days, purely cause its gonna send your blood sugars up, then you'll get hungry.
the protein content should out weigh the sugar content, however I seem to remember that in the Horizon programme they warned that high protein on a fast day actually caused some metabolic problems, however I can't remember what they said.
I think the health benefits are based on having a low level of protein in your fasting days. When your bod hasn't got protein source it goes into repair mode instead of build mode. That's the process that supposedly helps stops cancer and helps us live longer.
Bad sugars would interfere with the detox/insulin side of things.