Kidneys remove toxins from our blood and dispose of them through urine. Unless they're working properly, human bodies begin to retain fluid; when the bloodstream is at capacity, this fluid is held by the cells, and begins to build up in lungs, the heart cavity, and anywhere else it can find to deposit itself. Extremities swell, so rings and shoes fit tighter. Faces puff up, and maybe our waistbands feel a bit more snug. But the seriousness of fluid build-up can't be ignored when it begins to affect heart and lung function.

Most people experience some puffiness the day after an especially salty meal. The situation will resolve itself after a day or so, if the kidneys are working as they should, and a healthy person can help the situation along by drinking lots of water--this helps to literally flush excess sodium.

People with kidney (renal) failure don't have the luxury to indulge themselves, though; their kidneys struggle to process body fluids even on their best days. An overload of salt (sodium) in any form adds stress; taking in additional water does not help. In fact, in makes the situation worse. The combination of too much sodium and too much fluid can be life-threatening for kidney patients, whether or not they are on dialysis.

Serious kidney dysfunction is called "end stage renal disease." This diagnosis means that a person is on the road to a regimen of dialysis and possible kidney transplant. Physicians use urine and blood tests to determine the seriousness of each patient's condition and to prescribe medications and diet guidelines to control the symptoms and the progress of the disease.

This is one condition that needs to be controlled in very large part by diet. In fact, strict compliance with dietary guidelines can delay the onset of dialysis for months or years by reducing the stress on the kidneys.

When the dialysis does begin, diet modifications are in order. Specifics will depend on each person's unique health situation, and on the type of dialysis -- whether it's the kind done at home (peritoneal dialysis) or in a clinical setting (hemodialysis). What follows are general guidelines; these are in no way intended to replace a physician's or dietitian's recommendations. Consultation with a nutritional specialist is imperative; every patient's situation will be different!

FOR EVERY PATIENT WITH RENAL DISORDER:

SODIUM restrictions are paramount. It is literally impossible to take in NO sodium, because that's an element found in so many foods, but it is possible to limit the amount in a diet. First, obviously high sodium foods must be eliminated. These include cured meats (ham, sausage, bacon, corned beef, and the like), most cheeses, "fast" foods, pickles, bouillon cubes, soy sauce, and most Chinese or oriental foods.

Sodium hides in most commercially prepared foods, too; because salt is such a good preservative, it's used in packaging materials for cereal, bread, baking mixes, and most canned vegetables. This makes fresh food a wiser choice.

Some canned foods, such as vegetables, flaked fish or shellfish, poultry or meats, can be sodium-reduced by rinsing thoroughly. Place the food in a colander, rinse under running water for one full minute, and drain until all moisture is gone.

Even though it feels like a lot has been eliminated from diet choices (yes, pizza is tough to work into a low sodium eating plan) there are a myriad of ways to prepare delicious meals without high sodium content.

• Choose naturally low-sodium foods. As a rule, white cheeses are a safer bet than cheddar. Choose mozzarella, parmesan, ricotta, and look for low-salt varieties of your favorites. All unprocessed meats, poultry, and fish are acceptable. All fresh and frozen vegetables, all fruits and juices, and well-rinsed canned vegetables are suitable.

Homemade soups and noodles are healthier than the pre-made ones.

According to the specific limits of your own diet, it's okay to include moderately high sodium foods once in a while. Biscuits, a pancake, (homemade, to avoid the preservative salts of commercial mixes) cottage cheese, and sweet pickles or relish fall into this category.

• Look for no or low-salt versions of your favorite foods: tuna packed in water rather than oil, salt-free pretzels, unseasoned popcorn (dress up with chili powder, parmesan cheese, and a little garlic powder), no-salt butter are some examples.

• Collect a good selection of no-sodium seasonings; these can surprise people with spicy, robust taste independent of any salt.

• Keep an eye out for quick and easy low-sodium recipes for your favorite foods, and stock your pantry with the ingredients.

FLUIDS must be restricted. Your physician will set a limit for you, somewhere between four and eight cups maximum per day. Fluid is defined as anything that melts at room temperature, so in addition to water and juices, you must count ice cream, gelatin desserts, sherbet, and watermelon.

POTASSIUM counts, too, and it's harder to control for several reasons. You can't taste it, like you can salt, it's not a required item to be listed in the nutritional contents of packaged food, and it's in many foods.

The highest potassium amounts are found in nuts, avocados, potatoes, winter squash including pumpkin, oranges, kiwi, peaches, apricots, and anything dried -- fruits, beans and lentils.

Low potassium foods, safest to include frequently in a renal patient's diet, include applesauce, black berries, grapes, tangerines, canned pears and plums; asparagus, green or waxed beans, corn, cauliflower, cucumbers, water chestnuts, and summer squash. Juices such as apple, cranberry, lemonade, grape, and fruit-flavored drinks are okay; just remember to count them in your fluid total for the day.

PROTEIN plays an important role in the diet of any kidney patient. For those who are pre-dialysis, the amount must be limited to conserve kidney strength. After dialysis begins, however, protein needs to make up the major portion of the patient's menu, and the guideline will be set as a minimum, rather than a maximum amount per day -- as much as 2 grams per kilogram of body weight. The physician will determine the recommended amount for each person, depending on their over all health and their specific needs.

PHOSPHOROUS begins to be a consideration once dialysis begins, also. Foods to avoid based upon phosphorous content are dairy products, whole grains, bran and barley, nuts, coconut, figs and dates, raisins, salmon, sardines, oysters, and organ meats.

Cola drinks are also high in phosphorous, but soft drinks that are light colored (7-Up and Sprite, club soda) are fine.

Meat, poultry, fish and eggs are high in phosphorous, but are still an important part of the dialysis patient's diet because of the protein content; they should not be limited.

Because of the importance of limiting the amount of phosphorous in the blood stream, physicians will usually prescribe a "phosphate binder,"-- such as Tums--to be taken in prescribed doses with each meal.

While it seems like an inordinate amount of food has been eliminated from a wise menu plan for persons with renal failure, it is possible to have a healthy and delicious variety of food every day. A daily plan based on the amount of protein recommended for the individual patient, complemented by fresh, low-potassium fruits and vegetables and supplemented by low salt snacks, not only tastes wonderful, but is worth the effort in the life-saving health benefits achieved.