Personally I think that exercise should be limited during a fast.
The result would be better health at the end of the fast which would put someone in a better position for normalized weight following the fast.
If a body were perfectly healthy it should naturally have normal body weight.
I like to strive toward ideal health and I find that the weight takes care of itself.
People that shoot for weight loss alone most always gain all the weight back and usually more unless some changes are made in diet and exercise thereafter.
So to me, minimal to moderate physical activity during a fast brings the maximum health results which intern is better for normal weight in the long run.