Renal nutrition is concerned with the special dietary needs of kidney patients.
According to the National Kidney Foundation, more than 20 million Americans, one in nine adults, have chronic kidney disease, and an additional 20 million others are at increased risk. Kidney disease is a consequence of damaged nephrons, the tiny structures inside the kidneys that function as filters to remove wastes and extra fluids from the blood. It takes a long time to damage the kidney's nephrons, and the process usually occurs gradually over years. The most common causes of kidney disease include:
- Diabetes mellitus: Diabetes results from the body's inability to use the sugar glucose efficiently, either because it lacks insulin, the hormone that controls the level of glucose in the blood, or because it can not use the available insulin. The glucose stays in the blood and over time, high blood sugar levels can damage the kidneys.
- Hypertension: High blood pressure can damage the small blood vessels of the kidneys with the result that the kidneys can no longer filter wastes from the blood very well.
Conditions related to kidney failure and treatments
Anemia and Erythropoietin (EPO) —Anemia is common in people with kidney disease because the kidneys produce the hormone erythropoietin, or EPO, which stimulates the bone marrow to produce red blood cells. Diseased kidneys often don’t make enough EPO, causing the bone marrow to make fewer red blood cells. EPO is available commercially and is commonly given to patients on dialysis. Anemia can also contribute to heart problems.
Renal Osteodystrophy —This bone disease of kidney failure affects 90% of dialysis patients. The condition causes bones to become thin and weak or to form incorrectly and affects both children and adults. Symptoms can be seen in growing children with kidney disease even before they start dialysis. Older patients and women who have gone through menopause are at greater risk for this disease.
Itching (Pruritus )—Many patients treated with hemodialysis complain of itchy skin, which is often worse during or just after treatment. Itching can worsen from wastes in the bloodstream that current dialyzer membranes can’t remove from the blood. The problem can also be related to high levels of parathyroid hormone (PTH), which help control the levels of calcium and phosphorus in the blood.
Sleep disorders —Patients on dialysis often have insomnia, which can be caused by aching, uncomfortable, jittery, or “restless” legs (a condition related to nerve damage or chemical imbalances). Some patients may have sleep apnea syndrome, signaled by snoring and breaks in snoring. Sleep apnea may be related to the effects of advanced kidney failure on the control of breathing. Overtime, sleep disturbances can lead to “day-night reversal” (insomnia at night, sleepiness during the day), headache, depression, and decreased alertness.
Dialysis-related Amyloidosis (DRA) —It is common for patients who have been on dialysis for more than 5 years to develop DRA. It is the result of proteins in the blood depositing on joints and tendons, causing pain, stiffness, and fluid in the joints, as is the case with arthritis. Working kidneys filter out these proteins, but dialysis filters are not as effective.
SOURCE: National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, U.S. Department of Health and Human Services
(Illustration by GGS Information Services/Thomson Gale.)
- Heredity: Some kidney diseases result from hereditary factors, and run in families.
Kidney disease interferes with the vital function of the kidneys. The kidneys are bean-shaped organs located near the middle of the back, just below the rib cage. Kidneys filter blood, removing waste products and extra water , which become urine. They are very efficient filtering units, processing some 200 quarts of blood and producing about 2 quarts of urine per day in a healthy adult. The wastes in the blood result from the normal breakdown of active muscle and from digestion. After the body extracts nutrients from ingested food, the resulting waste is sent to the blood which is filtered by the kidneys. The kidneys also release three important hormones:
- Erythropoietin, which stimulates the bones to make red blood cells.
- Renin, which regulates blood pressure.
- The active form of vitamin D, required to regulate calcium for bones and for normal chemical balance in the body.
Damaged kidneys do not clean the blood efficiently. Instead, waste products and fluid build up in the blood leading to kidney disease that often cannot be cured. In the early stages of a kidney disease, treatment may be able to make the kidneys last longer. Eventually, kidneys may stop working altogether (kidney failure), and the body fills with extra water and waste products (uremia), which may lead to seizures or coma, and ultimately to death. When kidneys stop working completely, dialysis or a kidney transplantation is required.
Dialysis is an artificial way to filter blood after the kidneys have failed. With hemodialysis, the blood travels through tubes to a dialyzer, a machine that removes wastes and extra fluid. The cleaned blood is then returned to the body. The procedure is usually performed at a dialysis center three times per week for 3-4 hours. In peritoneal dialysis, a fluid (dialysate) is dripped into the abdomen to capture the waste products from the blood. After a few hours, the dialysate is drained out, and a fresh bag of dialysate is dripped into the abdomen. Patients can perform peritoneal dialysis themselves.
Renal nutrition is concerned with ensuring that kidney patients eat the right foods to make dialysis efficient and improve health. Dialysis clinics have dietitians on staff who help patients plan meals. Standard guidelines are: eating more high protein foods, and less high salt, high potassium, and high phosphorus foods. Patients are also advised on safe fluid intake levels. The National Kidney Foundation offers the following dietary advice to adults starting hemodialysis:
Sodium and salt>
- Use less salt and eat fewer salty foods to help to control blood pressure and reduce weight gains between dialysis sessions.
- Use herbs, spices, and low-salt flavor enhancers instead of salt.
- Avoid salt substitutes made with potassium.
Protein and meat
- People on dialysis need to eat more protein. Eat a high-protein food (meat, fish, poultry, fresh pork, or eggs at every meal, for a total of 8-10 ounces of high protein foods everyday.
Amyloidosis— Condition characterized by accumulation in body tissues of deposits of abnormal proteins (amyloids) produced by cells. Amyloidosis can lead to kidney disease.
B–group vitamins— Group of eight water-soluble vitamins that are often present as a single, vitamin complex in many natural sources, such as rice, liver and yeast.
Bulk minerals— Minerals needed by the body in small amounts (RDA > 200mg/day) They include: calcium, magnesium, phosphorus, potassium, sodium, and sulfur.
Diabetes mellitus— A condition characterized by high blood sugar levels resulting from the body's inability to use glucose efficiently. There are two types of diabetes: type 1 and type 2.
Dialysis— The process of cleaning wastes from the blood artificially. This is normally done by the kidneys but if the kidneys fail, the blood must be cleaned artificially with special equipment.
Dialysis–related amyloidosis (DRA)— Type of amy-loidosis resulting from the use of dyalisis.
Digestion— The process by which food is chemically converted into nutrients that can be absorbed and used by the body.
Glucose— A monosaccharide sugar occurring widely in most plant and animal tissue. In humans, it is the main source of energy for the body.
Hemodialysis— Type of dialysis to clean wastes from the blood after the kidneys have failed: the blood travels through tubes to a dialyzer, a machine that removes wastes and extra fluid. The cleaned blood then goes back into the body.
High blood pressure— Blood pressure is the force of the blood on the arteries as the heart pumps blood through the body. High blood pressure, or hypertension, is a condition where there is too much pressure, which can lead to heart and kidney problems.
Hormone— Substance produced in one part of the body and released into the blood to trigger or regulate particular functions of the body. The kidney releases three hormones: erythropoietin, renin, and an active form of vitamin D that helps regulate calcium for bones.
Insulin— Hormone released by the pancreas in response to increased levels of blood sugar (glucose) in the blood.
Micronutrients— Nutrients needed by the body in small amounts. They include vitamins and minerals.
Nephrons— A tiny part of the kidneys. Each kidney is made up of about 1 million nephrons, which are the working units of the kidneys, removing wastes and extra fluids from the blood.
Nutrient— A source of nourishment, especially a nourishing ingredient in a food.
Trace minerals— Minerals needed by the body in tiny, trace amounts (RDA <200mg/day). They include: selenium, iron, zinc, copper, manganese, molybdenum, chromium, arsenic, germanium, lithium, rubidium, tin.
Type 1 diabetes— In type 1 diabetes, the pancreas makes little or no insulin.
Type 2 diabetes— In type 2 diabetes, the body is resistant to the effects of available insulin. It is the most common form of diabetes mellitus. Most of the people who have this type of diabetes are overweight.
- Even though peanut butter, nuts, seeds, dried beans, peas, and lentils have protein, they are generally not recommended because they are high in both potassium and phosphorus.
Grains and cereals
- 1 slice of bread (white, rye, or sourdough)
- 1/2 English muffin
- 1/2 bagel
- 1/2 hamburger bun
- 1/2 hot dog bun
- 1 6-inch tortilla
- 1/2 cup cooked pasta
- 1/2 cup cooked white rice
- 1/2 cup cooked cereal (cream of wheat)
- 1 cup cold cereal (corn flakes or crispy rice)
- 4 unsalted crackers
- 11/2 cup unsalted popcorn
- 10 vanilla wafers
Milk, yogurt, and cheese
Most dairy foods are very high in phosphorus and intake of milk, yogurt, and cheese should be limited to 1/2 cup milk or yogurt or 1 ounce of cheese per day. Dairy foods low in phosphorus include:
- Butter and tub margarine
- Cream cheese
- Heavy cream
- Ricotta cheese
- Brie cheese
- Non-dairy whipped topping
Fruits and juices
All fruits have some potassium. Some fruits however, have more than others. Star fruit (carambola) should be always avoided. Other fruits that should be limited or totally avoided are:
- Oranges and orange juice
- Prunes and prune juice
- Raisins and dried fruit
- Melons (cantaloupe and honeydew) 2-3 servings of the following low potassium fruits should be eaten each day. One serving = 1/2 cup or 1 small fruit or 4 ounces of juice.
- Apple (1)
- Berries (1/2 cup)
- Cherries (10)
- Fruit cocktail, drained (1/2 cup)
- Grapes (15)
- Peach (1 small fresh or canned, drained)
- Pear, fresh or canned, drained (1/2)
- Pineapple (1/2 cup canned, drained)
- Plums (1 or 2)
- Tangerine (1)
- Watermelon (1 small wedge)Drinks may include:
- Apple cider
- Cranberry juice cocktail
- Grape juice
All vegetables contain some potassium, but some have more than others and should be limited or totally avoided. Examples are:
- Potatoes (including French fries, potato chips and sweet potatoes)
- Tomatoes and tomato sauce
- Winter squash
- Beet greens
- Cooked spinach
- Parsnips and rutabaga
Patients are advised to eat 2-3 servings of the following low-potassium vegetables each day. One serving =1/2 cup.
- Green and wax beans
- Lettuce-all types (1 cup)
- Peppers-all types and colors
- Zucchini and yellow squash
- Depending on calorie needs, the dietitian may recommend high-calorie deserts such as pies, cookies, sherbet, and cakes.
- Dairy-based desserts and those made with chocolate, nuts, and bananas should be limited.
The special diet followed by kidney patients requires taking several precautions. The National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC)of the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) offers the following general guidelines:
- Fluids. A dietitian helps dialysis patients determine how much fluid to drink each day. This is because extra fluid can raise blood pressure, make the heart work harder, and increase the stress of dialysis treatments. Many foods, such as soup, ice cream, and fruits, also contain plenty of water and the dietitian is the best person to provide advice on controlling thirst.
- Potassium. Potassium is a bulk mineral found in many foods, especially fruits and vegetables. It affects how steadily the heart beats, and this is why eating high-potassium foods can be very dangerous for the heart. Foods like oranges, bananas, tomatoes, potatoes, and dried fruits must be avoided. Some potassium can be removed from potatoes and other vegetables by peeling and soaking them in a large container of water for several hours before cooking them in fresh water.
- Phosphorus. Phosphorus is another mineral found in foods. It can weaken bones and make skin itch if intake is too high. Control of phosphorus is very important for the prevention of bone disease and associated complications. High-phosphorus foods include milk and cheese, dried beans, peas, colas, nuts, and peanut butter and should be avoided.
- Sodium (salt). Another mineral present in many foods is sodium. Most canned foods and frozen dinners contain high amounts of sodium. A high sodium intake causes thirst and drinking more fluids, which makes the heart work harder to pump the fluid through the body. Over time, this can cause high blood pressure and congestive heart failure. Kidney patients are accordingly advised to eat fresh foods that are naturally low in sodium, and to look for products labeled “low sodium.”
- Protein. Most kidney patients on dialysis are encouraged to eat as much high-quality protein as they can. Protein helps maintain muscle and repair tissue, but it breaks down into blood urea nitrogen (BUN) in the body. However, some sources of protein, called high-quality proteins, produce less waste than others. High-quality proteins are found in meat, fish, poultry, and eggs. Obtaining dietary protein from these sources can reduce the amount of urea in blood.
- Calories. Calories provide energy to the body and some dialysis patients need to gain weight. Vegetable oils, such as olive, canola, and safflower oils, are good sources of calories and do not result in cholesterol problems. Hard candy, sugar, honey, jam, and jelly also provide calories and energy. However, kidney patients with diabetes must follow the guidance of a dietitian.
Since dialysis patients must avoid several types of foods, their diet may be missing important vitamins and mineral micronutrients. Dialysis also removes some vitamins from the body. The treating physician may prescribe a vitamin and mineral supplement designed specifically for kidney failure patients. The physician may also prescribe vitamin C and a group of vitamins called B complex. A calcium tablet may also be given to bind the phosphorous present in food and provide the extra calcium needed by the body. Patients should never take off-the-counter supplements since they may contain vitamins or minerals that may cause harmful interactions.
Kidney patients on dialysis have very special dietary needs that exceed restricting foods, because eating poorly can increase the risk of complications. This is why a dietitian is such a crucial member of the healthcare team. The dietitian will keep track of the fat and muscle stores in a patient's face, hands, arms, shoulders, and legs. The dialysis care team will look for changes in the blood level of proteins, especially the albumin level, as a change in this protein can be indicative of body protein loss. Special blood tests are also done on a monthly basis. They include Kt/V and urea reduction ratio (URR) tests. The tests are used by the care team to evaluate the appropriate course of dialysis required to help patients feel best. A change in any of these tests could mean that a patient is not getting enough dialysis. The tests also provide information about a patient's protein intake and on the protein equivalent of nitrogen appearance (PNA). Using the PNA, the albumin results and any changes in patient appetite, the dietitian can determine if the intake of the right foods is adequate.
Kidney patients are at risk of developing complications such as high blood pressure, anemia (low blood count), weak bones, poor nutritional health and nerve damage. Also, kidney disease increases the risk of heart and blood vessel (cardiovascular) disease.
Patients undergoing dialysis can also experience side effects, caused by rapid changes in the body's fluid and chemical balance during treatment. Two common side effects are muscle cramps and hypotension. Hypotension can make the patient feel weak, dizzy, or nauseous. Fortunately, dialysis side effects can often can be treated quickly and easily.
In patients receiving dialysis, a type of protein called beta-2-microglobulin builds up in the blood. As a result, beta-2-microglobulin molecules tend to join together to form aggregated molecules (amyloids). These aggregates can form deposits and eventually damage the surrounding tissues while causing significant discomfort. This condition is called dialysis–related amyloidosis (DRA). DRA is relatively common in patients, especially older people, who have been on hemodialysis for more than five years. This is because dialysis membranes after being used for several years do not effectively remove the beta-2-microglobulin amyloids from the bloodstream. New hemodialysis membranes, as well as peritoneal dialysis, remove beta-2-microglobulin more effectively, but not enough to keep blood levels normal. As a result, blood levels remain elevated, and deposits formin bone, joints, and tendons.
The two major problems faced by children with kidney failure are poor growth and weight gain, so their diet is usually not restricted unless needed. Children grow fastest during the first two years of life and the earlier the age at which kidney failure occurs, the more likely is growth to be affected. The goals in feeding a child with kidney failure are to balance nutrition for normal growth and protect health as well. The treating physician works with a dietitian to monitor possible problems and suggests, if needed, a diet that will try to take into account the child's food likes and dislikes.
Parents should learn as much as they can about a child's kidney disease and its treatment, encouraging the child to ask questions not only to family members but also to doctors, nurses, and other members of the care team. This also includes explaining the special nutrition restrictions of kidney disease. If explained clearly and simply, even very young children can understand special dietary needs. It is found on the whole that children are in general more compliant with dietary restrictions than adults. One way to help children develop a sense of control over the illness is to have a child make a list of favorite foods and take him or her along to dietitian appointments to see if these foods can be incorporated into the diet plan. Trying to bribe or force a child to eat is ill-advised and counterproductive. Helping a child understand kidney disease, its treatment and the purpose of the special diet is the only way to ensure dietary compliance while maintaining a positive climate of support and encouragement.
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American Association of Kidney Patients (AAKP). 3505 E. Frontage Rd., Suite 315, Tampa, FL 33607. 1-800-749-2257. <www.aakp.org>.
American Dietetic Association (ADA). 120 South Riverside Plaza, Suite 2000, Chicago, IL. 60606-6995. 1-800/877-1600. <www.eatright.org>.
American Society for Nutrition (ASN). 9650 Rockville Pike, Bethesda, MD 20814. (301) 634-7050. <www.nutrition.org>.
National Kidney Foundation. 30 East 33rd Street, New York, NY 10016. 1-800-622-9010. <www.kidney.org>.
National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC). 3 Information Way, Bethesda, MD 20892–3580. <kidney.niddk.nih.gov>.
Renal dieticians (RPG). 120 South Riverside Plaza, Suite 2000, Chicago, IL. 60606-6995. 1-800-877-1600 ext. 4815. <www.renalnutrition.org>.
Monique Laberge, Ph.D.