Final answer:
When sodium and water intake is greater than output, causing isotonic gain, there is no change in the osmolarity of body fluids, resulting in an isotonic gain.
Step-by-step explanation:
In a situation where the intake of sodium and water is greater than the output, causing isotonic gain, there would be no change in the osmolarity (concentration of solute) of the body fluids. This is known as an isotonic gain. The relative concentrations of solute and solvent on both sides of the membrane remain equal, so there is no net water movement and therefore no change in the size of the cells.