is there any evidence for this ? I was under the impression they were all broken down into glucose and fructose in the stomach (or mouth – if you suck a piece of bread a little it will become sweet)
Saliva does contain an enzyme specific for starch hydrolysis (amylase), but as little food these days is sucked it plays a minor role.
Most monosaccahrides are produced by the action of pancreatic enzymes in the duodenum, the stomach plays little or no role as it's low pH is not compatible with the action of the enzymes required.
but isn't that a "non answer" answer ? OK I was wrong about the exact location of the breakdown, as it's not in the stomach, but every reference I've located so far says the intestines only take in monosaccahrides, not disaccharides or polysaccharides…