Please post your recipe and process. There are multiple ways to lighten the body of a beer without resorting to adjuncts. Unless you are trying to make Budweiser, then there may be something more appropriate. For example, I'm assuming you are doing an all grain recipe as rice for a substitute would be bizarre in just about any other circumstance. But one way to lighten the body is to decrease the mash temp to make the wort more fermentable. If you are currently mashing this recipe at 154, reduce the mash temp to 148. This will make the wort more fermentable and the increased attenuation will make the body lighter.
Just subbing out rice for two row, you can sub 1 for 1, but understand that rice must be mashed with a base grain. Plus, you should not use more than 2 lbs of rice in a 5 gallon batch.
