Could you please clarify what you mean by "fruit sugar"? I thought that the sugar present in fruit was fructose. If this is incorrect, and fruit actually contains fructose, sucrose and glucose, then are there any food source that solely contain fructose?? I am getting ready to experiment with some of the suggestions in Cordain's book, but am aprehensive about adding "unlimited" fruit after years of low-carbing. The reason I want to experiment is that I am hoping fruit could help with the constipation I invariably experience when going ultra-low carb, and I also thought it could replenish glycogen stores. I simply tire out way too soon when working out after weeks of ultra low-carbing. I am thinking of only eating fruit during a meal that also contains protein to blunt any insulin spikes. Thoughts??