Whats the difference between brown rice and sweet potato in terms of GI and calories?

The glycemic index of brown rice is 50 to 66, the GI of sweet potato typical sweet potatoes you'd find in the UK, USA or Canada is about 60 if you prepare it by chopping it into cubes and boiling it (although some varieties can go as low as 40 and some as high as 78.

As far as calories, you have to look that up and prepare the appropriate serving size.

The advantage of the sweet potato is that it has almost zero sodium and is very high in potassium. This makes them ideal food for the 4 or 5 days before a photo shoot, bodybuilding contest, going to the beach, or when you want to shed that last bit of water.