The terminology free sugars is possibly related to mono and dissacharides. It is not clear to me if it means precisely just refined sugars or both, refined and not refined.
For example, glucose is an energy source for the metabolism. Limiting that sounds counterintuitive. It has been suggested that it is cariogenic, but it doesn't seem enough of a reason for limitation, as we could ingest it without much contact to the teeth, so that is would be dissolved only in the stomach.
So, what are the unhealthy facts related to free sugars that imply reducing the intake?