You said you were trying to reduce
oil consumption. Did you mean
fuel consumption?
If it's using oil, it is most likely burning it. So oil is getting into the combustion chamber somehow. A thinner oil will flow more easily (that's what "thinner" means) and so more of it will leak into the chamber, getting burned. So the vehicle will probably use more oil if you go to a thinner one.
A thinner oil is easier to pump around, though, so it will give you (very slightly!) better fuel economy. I'm not sure the difference will be enough to measure, though.
What oil weight is called for by the owner's manual? There is a specified oil, or more likely a range of oils, and it's best to stick to that range. If you're looking to keep oil use down, go for something on the thicker (higher numbers) end of that range, and if you're looking for best fuel economy, use something on the thinner end of that range.
....Then again, driving style will give you a lot more MPGs than thinner oil ever could, so it might be best to concentrate on that rather than worry about which oil to use...
-soD