Salt and Water Excess

Salt (sodium chloride) problems are much more prevalent in patients with kidney disease than water problems and are not as easy to treat. One reason is that humans don't have true salt hunger (or salt satiety), as many species of animals do. So we continue to consume salt (or to avoid it) whatever the needs of our body may be. By contrast, when we need water, we get thirsty.

Americans eat more salt than people in many societies, and it is particularly difficult for us to learn to eat foods without added salt. As the kidney is the only route for salt elimination, problems with salt retention are extremely common in patients with kidney disease. This is a universal problem in patients who have the nephrotic syndrome, as explained in Chapter 18. Salt retention always entails retention of a certain amount of water, as well, for reasons already explained: If you take salt with little or no water, you get thirsty because the concentration of dissolved solids in your body fluids has increased. Your brain releases antidiuretic hormone. These two responses result in increased intake of fluids and decreased excretion of urine, which together cause an increase in the amount of water in the body and a return to the normal level in the concentration of dissolved solids.

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