What are the effects of someone on dialysis drinking soft drinks without sugar?

Excess fluid: It is not the sugar, unless the person is also a diabetic, but the amount of fluid. Those on dialysis are restricted fluid intake. There are other dietary restrictions.

Depends: If you are on dialysis, the less sugar in the diet, the better. However certain soft drinks like dark sodas (coke, pepsi) have a high concerntraion of phosphorus. Dialysis patients must avoid high phosphorus foods or these levels will lead to calcifications and bone disease.