On first principles, it's an epimer (a sort of stereoisomer) of fructose which unlike all other monosaccharides bypasses the liver first pass effect which evolved to protect the body from toxins. Renal elimination is the only way the body can get rid of it (diabetics also get rid of much glucose this way). Chronically high levels of glucose in the blood are very toxic, mostly by glucose randomly attaching itself to proteins and breaking them. Fructose does the same thing except it's 5x more reactive than glucose and the liver metabolizes all of it in the first pass. (we've evolved to exclude all common monosaccharides from the bloodstream, except glusose in the precise quantities necessary for energy production and storage) Based on all that, my credence for allulose being at least somewhat harmful is 95%. However it remains unclear whether the magnitude of the harm is sufficient to show up in weak studies, and most of those studies will be funded by the manufacturer. It is going to be dose dependent and I don't know whether the renal elimination half life is faster than other monosaccharides. This market is about whether there will be a reputable meta-analysis (by Cochrane or similar) purporting that allulose is harmful to humans, before 2050.