"Shunt" has two meanings, which I think you are confusing.
If you put a "shunt resistor" in series with the load (your body), then measuring the voltage across it with a meter or 'scope gives you the current through the load. The shunt resistor should be a value lower than the actual load.
"Shunt" also means parallel, so placing a large resistor in parallel with the output as a load can simulate your body resistance to measure the output voltage under load.
Your measurement of 600 k ohms body resistance may be too high.