Low cal diet causes. Relative dehydration d/t low intake of salt that makes people not thirsty so they don't drink, also the body does not hang on to its fluids. See how much you drink when you eat the salty pizza! Some sensitive people even swell in legs after that! So, if your diet does not have salt at all you may benefit from a cup of broth daily or a piece of pickle and 8 cups of fluid intake. Avoid that if chf.