If it's white rice, there shouldn't be much if any, as the antinutrients were in the part that was removed, so it's not very different from eating a load of sugar.
It's possible, though I've never heard of puffed brown rice.
Kurt Harris eats it, for what that's worth. I agree with raydawg that most of the antinutrients have been removed. And, if you get the generic brand, there usually isn't any added sugar (rice krispies have some added sugar). I don't agree that it's necessarily similar to eating a load of sugar as it would have much less fructose (if any?) than sugar. It should be mostly starch. I think it's fine in moderation as a source of carbohydrate and/or calories as long as you are eating other more nutrient dense foods also. And I'd maybe avoid it if trying to lose weight.
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