Your body will tolerate sodium only in certain concentration. The more salt you eat, the more water your system retains to dilute it. But getting rid of unneeded salt is easy just drink more water. As water is forced through the kidneys, it takes away excess sodium. The overweight person needs more water than the thin one.
Larger people have larger metabolic loads.
Since we know that water is the key to fat metabolism, it follows that the overweight person needs more water. Water helps to maintain proper muscle tone by giving muscles their natural ability to contract and by preventing dehydration. It also helps to prevent the sagging skin that usually follows weight loss shrinking cells are buoyed by water, which plumps the skin and leaves it clear, healthy and resilient. Water helps rid the body of waste. During weight loss, the body has a lot more waste to get rid of all that metabolized fat must be shed.