What it is
A rare sugar found in traces in figs and maple, manufactured in bulk — it tastes and browns like sugar at ~70% the sweetness, but your body barely uses it. The FDA exempts it from the "added sugars" line.
Why your biology objects
About 70% is absorbed and then excreted intact in the urine, unmetabolized — so despite being a fructose epimer it doesn't enter the liver's fructose pathway, raise blood glucose, or drive de novo lipogenesis. Genuinely close to inert; the only real caveats are that long-term human data are still thin and large doses can cause GI upset.