US Pharm. 2014;39(8):48-52.
 
The kidneys have two primary roles: to filter extra water and waste products from the blood and to balance the salts and minerals—such as calcium, phosphorus, sodium, and potassium—that circulate in the blood. The kidneys also release hormones that help make red blood cells, regulate blood pressure, and keep bones strong.1
 
More than 20 million Americans may have kidney disease and many more are at risk. The main risk factors for developing kidney disease are diabetes, high blood pressure, cardiovascular disease, and a family history of kidney failure. In general, anyone can develop kidney disease, regardless of age or race, and it has become a growing problem.1
 
There are two main forms of kidney disease—acute kidney injury, which is often reversible with adequate treatment, and chronic kidney disease (CKD), which is often not reversible. In both cases, there is usually an underlying cause. CKD occurs slowly over many years, often due to diabetes or high blood pressure, while acute kidney injury happens because of illness or trauma or as an effect of certain medications. This can occur in a person with normal kidneys or in someone who already has kidney problems.1
 
A person may prevent or delay some health problems from CKD by eating the right foods and avoiding foods high in sodium, potassium, and phosphorus. In addition, learning about calories, fats, proteins, and fluids is important for a person with advanced CKD. High-protein foods such as meat and dairy products break down into waste products that only healthy kidneys can remove from blood.2
 
As CKD progresses, nutritional needs change. A healthcare provider may recommend that a patient with reduced kidney function choose foods carefully using medical nutrition therapy.

Pathophysiology

Renal failure is mainly determined by a decrease in the glomerular filtration rate, the rate at which blood is filtered in the glomeruli of the kidney. This is detected by a decrease in or absence of urine production or by determination of waste products (creatinine or urea) in the blood. Depending on the cause, hematuria and proteinuria may be noted.
 
As mentioned above, CKD usually takes a long time to develop and does not go away. In early stages, the kidneys continue to work, but not as well as they should. Wastes may gradually build up and the body becomes accustomed to those wastes. Salts containing potassium and phosphorous may reach high and unsafe levels, causing heart and bone issues. Anemia can result from CKD when the kidneys do not make enough erythropoietin, a hormone that causes the bone marrow to make red blood cells. After months or years, CKD may progress to end-stage renal disease, which requires a kidney transplant or regular weekly blood filtering treatments through dialysis.3
 
In renal failure, there may be problems with increased fluid in the body (leading to swelling), increased acid levels, raised levels of potassium and phosphates, decreased levels of calcium, and, in later stages, anemia and bone problems. Long-term kidney problems are associated with an increased risk of cardiovascular disease.
 
A third form of renal failure is a condition called acute-on-chronic renal failure. The acute part of this disease may be reversible, and the goal of treatment, as with the acute form, is to return the patient to baseline renal function, typically measured by serum creatinine. This condition can be difficult to distinguish from chronic kidney disease if the patient has not been monitored by a nephrologist and no baseline blood work is available for comparison.3

Genetic Predisposition

Genetic studies have proposed a gene APOL1 as a major genetic risk locus for a spectrum of nondiabetic renal failures in individuals of African origin and for hypertension not attributed to other etiologies. Two Western African variants in APOL1 have been shown to be associated with end-stage renal disease in African Americans and Hispanic Americans.3

Medical Nutrition Therapy

Medical nutrition therapy (MNT) is the use of nutrition counseling by a registered dietitian to help promote a medical or health goal. Most nephrologists refer their patients to a registered dietitian to help with their food plan. Many insurance policies cover MNT when recommended by a healthcare provider. Anyone who qualifies for Medicare can receive a benefit for MNT from a registered dietitian or nutrition professional, provided that a healthcare provider indicates that the person has diabetes or kidney disease. Dietitians who specialize in helping people with CKD are called renal dietitians.4
 
As CKD progresses, people often lose their appetites because they find that foods do not taste the same. As a result, they consume fewer calories and lose too much weight. Renal dietitians can help people with advanced CKD find healthy ways to add calories to their diet. TABLE 1 lists the signs and symptoms of CKD.5
 
During continuous renal replacement therapy, including dialysis, the daily recommended energy allowance is between 25 and 35 kcal/kg, with a ratio of 60%-70% carbohydrate to 30%-40% lipids and between 1.5 and 1.8 g/kg protein. Supplemental vitamin B1 (100 mg/day), vitamin C (250 mg/day), and selenium (100 mcg/day) are also recommended.4
 
The following food ingredients play an important role in the nutritional health of patients with kidney disease.

Proteins

Proteins help build and maintain muscle, bone, skin, connective tissue, internal organs, and blood and are an essential part of any diet. They help fight disease and heal wounds. But proteins also break down into waste products that must be removed from the blood by the kidneys. Eating more protein than the body needs may put an extra burden on the kidneys and cause kidney function to decline faster.1
 
People with CKD should eat moderate or reduced amounts of protein; however, restricting protein could lead to malnutrition. The typical American diet contains more than enough protein. Most people—with or without CKD—can get the daily protein they need by eating two 3-oz servings of meat or meat substitute. In general, a 3-oz serving of meat is enough daily protein for a normal person (1 g protein generates 3.4 kcal).6
 
A renal dietitian can help people learn about the amount and sources of protein in their diet. With careful meal planning, a well-balanced vegetarian diet can also provide these nutrients. A renal dietitian can help people with advanced CKD make small adjustments in their eating habits that can result in significant protein reduction. The following lists include high-protein foods and suggestions for low-protein alternatives that are better choices for people with CKD trying to limit their protein intake.6
 
High-protein foods include ground beef, halibut, salmon, tuna, and chicken breast, while low-protein alternatives encompass egg substitutes, shrimp, tofu, crabmeat, roasted chicken, and beef stew.8
 
We have to remember that when kidney function declines to the point where dialysis becomes necessary, patients should include more protein in their diet because dialysis removes large amounts of protein from the blood.

Fats

It is important to know the sources of fat in one’s diet, because some fats are healthier than others. Eating the wrong kind of fat and too much fat increases the risk of clogged blood vessels and heart problems. Fat provides energy; helps produce hormone-like substances that regulate blood pressure and other heart functions; and carries fat-soluble vitamins. People with CKD are at higher risk of having a heart attack or stroke. As a result, these patients should be especially careful about how dietary fat affects their heart health (1 g of fat generates 9 kcal).2
 
Saturated fats and trans-fatty acids can raise blood cholesterol levels and clog blood vessels and have to be eliminated from diet in advanced CKD. Saturated fats are found in animal products, and these fats are usually solid at room temperature. Trans-fatty acids are often found in commercially baked goods such as cookies and cakes and in fried foods like doughnuts and French fries. Hydrogenated vegetable oils, found in margarine and shortening, should be avoided because they are high in trans-fatty acids.6
 
A dietitian can suggest healthy ways to include fat in the diet, especially if more calories are needed. Vegetable oils and monounsaturated fats are healthy alternatives to animal fats. The following list shows the sources of fats, broken down into three types.8
 
Saturated fats: red meat, poultry, whole milk, butter, and lard
 
Trans-fatty acids: commercial baked cakes, French fries, and doughnuts
 
Monounsaturated fats: corn oil, safflower oil, olive oil, coconut oil, and canola oil.

Sodium

People with CKD should limit fluid buildup in the body. The extra fluid raises blood pressure and puts a strain on the heart and kidneys. A dietitian can help CKD patients find ways to reduce the amount of sodium in their diet. Too much sodium causes blood to hold fluid. The FDA recommends that all people should limit their daily sodium intake to no more than 2,300 mg, the amount found in 1 tsp of table salt. People who are at risk for a heart attack or stroke because of a condition such as high blood pressure or kidney disease should limit their daily sodium intake to no more than 1,500 mg. Food labels provide information about the sodium content in food. Canned foods, some frozen foods, snack foods, and most processed meats have large amounts of salt.1
 
Alternative seasonings can help people reduce their salt intake. People with advanced CKD should avoid salt substitutes that use potassium, because CKD limits the body’s ability to eliminate potassium from the blood. The list below provides some high-sodium foods and suggestions for low-sodium alternatives that are healthier for people with any level of CKD who have high blood pressure.2
 
High-sodium foods: salt, hot dogs and canned meat, packaged rice with sauce, packaged noodles with sauce, frozen vegetables with sauce, frozen prepared meals, regular canned vegetables, canned soup, regular tomato sauce, and snack foods.
 
Low-sodium alternatives: salt-free herb seasonings, low-sodium canned foods, frozen vegetables without sauce, fresh-cooked meat, plain rice, plain noodles, fresh vegetables, homemade soup with fresh ingredients, reduced-sodium tomato sauce, unsalted pretzels, and popcorn.8

Potassium

Keeping the proper level of potassium in the blood is essential. Potassium keeps the heart beating regularly and the muscles working properly. Problems can occur when blood potassium levels are either too low or too high. Damaged kidneys allow potassium to build up in the blood, causing serious heart problems. Potassium is found in many fruits and vegetables, and people with advanced CKD may need to avoid these foods. Blood tests can indicate when potassium levels have climbed above normal range. A renal dietitian can help people with advanced CKD find ways to limit the amount of potassium they eat. The potassium content of potatoes and other vegetables can be reduced by boiling them in water. The following list gives examples of some high-potassium foods and suggestions for low-potassium alternatives for people with advanced CKD.6
 
High-potassium foods: oranges and orange juice, melons, bananas, potatoes, tomatoes, sweet potatoes, cooked spinach and broccoli, molasses, prunes, yogurt, fish, milk, soybeans, winter squash, and beet greens.
 
Low-potassium foods: apples, apricots, grapes, plums, lemons, alfalfa sprouts, bamboo shoots, bean sprouts, beets, blackberries, blueberries, and cabbage.8

Phosphates

Damaged kidneys allow phosphorus, a mineral found in many foods, to build up in the blood. Too much phosphorus in the blood pulls calcium from the bones, making them weak and prone to breaking. Too much phosphorus may also make skin itch. A renal dietitian can help people with advanced CKD learn how to limit phosphorus in their diet.6
 
As CKD progresses, a person may need to take a phosphate binder such as sevelamer hydrochloride (Renagel), lanthanum carbonate (Fosrenol), calcium acetate (PhosLo), or calcium carbonate (Tums) to control the phosphorus in the blood. These medications act like sponges to soak up, or bind, phosphorus while it is in the stomach. Because it is bound, the phosphorus does not get into the blood. Instead, it is removed from the body in the stool.7
 
The following list includes high-phosphorus foods and suggestions for low-phosphorus alternatives that are healthier for people with advanced CKD.
 
High-phosphorus foods: dairy foods (milk, cheese, yogurt), beans (baked, kidney, lima, pinto), nuts and peanut butter, processed meats (hot dogs, canned meat), cola, canned iced teas and lemonade, bran cereals, and egg yolks.
 
Low-phosphorus alternatives: liquid nondairy creamer, pasta, legumes, shellfish, sherbet, cooked rice, nut and seed products, wheat, corn, cereals, popcorn, peas, lemon-lime soda, root beer, powdered iced tea, and lemonade mixes.8

Fluids

People with advanced CKD may need to limit how much they drink because damaged kidneys cannot remove extra fluid. The fluid builds up in the body and strains the heart. Patients should tell their healthcare provider about any swelling around the eyes or in the legs, arms, or abdomen.
 
The following fruits and vegetables make the body water content higher and should be used in moderate amounts: cucumbers, iceberg lettuce, celery, radishes, green peppers, cauliflower, watermelon, star fruit, cantaloupe, grapefruit, and tomatoes (water content between 85% and 95%).

Laboratory Reports

Understanding laboratory reports allows a person to see how different foods can affect the kidneys. Patients with CKD can ask their healthcare provider for regular blood and urine tests and to have any results out of the normal range explained. Keeping track of these laboratory results can help people see whether they are making progress or getting worse. Renal dietitians can make healthier food choices for their patients. As an example, if a test shows that a person with advanced CKD has a high potassium level (normal range 3.5-5.1 mmol/L), that person should concentrate on reducing potassium in the diet by limiting high-potassium foods.7

REFERENCES

1. Mitch WE. Chronic kidney disease. In: Goldman L, Schafer AI, eds. Goldman Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2012:chap 132.
2. Eat right to feel right on hemodialysis. NIH Publication No. 08-4274. September 2, 2010. www.kidney.niddk.nih.gov/KUDiseases/pubs/eatright/. Accessed May 2, 2014.
3. Abboud H, Henrich WL. Clinical practice. Sage IV chronic kidney disease. N Engl J Med. 2010;362:56-65.
4. Medical Nutrition Therapy. United States Department of Agriculture (USDA) National Nutrient Database for Standard Reference. www.ars.usda.gov/SP2UserFiles/Place/12354500/Data/SR25/nutrlist/sr25a203.pdf.2012. Accessed April 14, 2014.
5. Shoji T, Nishizawa Y. Chronic kidney disease as a metabolic syndrome with malnutrition—need for strict control of risk factors. Intern Med. 2005;44:179-187.
6. Castaneda C, Gordon PL, Uhlin KL, et al. Resistance training to counteract the catabolism of a low-protein diet in patients with chronic renal insufficiency. A randomized, controlled trial. Ann Intern Med. 2001;135:965-976.
7. Johansen KL. Exercise and chronic kidney disease: current recommendations. Sports Med. 2005;35:485-499.
8. Nutrition and chronic kidney diseases, 1998-2006. National Kidney Foundation, Inc. www.kidney.org/atoz/pdf/nutri_chronic.pdf. Accessed May 20, 2014.
 
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