When stationary in N; revs are at "idle" setting. Car consumes minimum fuel.

When in D but stationary via hand-break; revs go down slightly BUT, due to loading as car tries to move, the EFI enriches the air-fuel mixture. Car consumes almost same as previous case... probably exactly the same.

When in D via foot brake; revs go slightly lower than above because foot break vacuum chamber uses intake suction pressure. EFI enriches air-fuel mixture even farther. Car consumes more fuel than when on hand break.... but just slightly more than when in N.

Conclusion: if you want to save fuel, turn off the engine completely each time you stop... but your savings might be eaten by the extra wear on your starter...

I think when on N, the engine is free, not loaded and that's why the rpm goes slightly up. It has nothing to do with consuming more.
Think of it this way, when your car is loaded to capacity with luggage or passengers and you floor the accelerator, what happens? Compare that to when the car has the driver only [not loaded] and its downhill and you floor the accelerator, what happens?
Does it mean loaded to capacity or uphill a car consumes less just coz the rpm doesn't goes as high as when on a downhill and not loaded?

It all depends on how the engine is "loaded".
D and not moving consumes slightly more fuel than when on N ,since the engine is not free.

@Mckeind uv nailed it neatly Shift to Neutral

Copy pasted this to some female mates here..

I am the man of the week...

You are thinking exactly like me and guest what, you and I are right.