NUTRITION in KIDNEY DISORDER (CKD)

RENAL PHYSIOLOGY

The kidneys keep the body’s fluids, electrolytes, and organic solutes in a healthy balance or homeostasis.

Their functional units are the millions of nephrons in the renal cortex which filter most constituents of the blood other than red blood cells and protein, reabsorb needed substances, secrete hydrogen ions to maintain acid-base balance, maintains blood pressure and secrete wastes.

Urine formation consists of four basic processes:

1. glomerular filtration

2. tubular reabsorption

3. tubular secretion and

4. urine concentration.

Several disease conditions can interfere with these functions.

Inflammatory and degenerative diseases can involve the small blood vessels and membranes in the nephrons.

Urinary tract infections and kidney stones can interfere with normal drainage, causing further infection and tissue damage.

Circulatory disorders, such as hypertension, can damage the small renal arteries.

Other diseases, such as diabetes, gout, and urinary tract abnormalities can lead to impaired function, infection, or obstruction.

Toxic agents such as insecticides, solvents, and certain drugs may also harm renal tissue.

Nephrotic Syndrome

In nephrotic syndrome, an injury to the glomerular basement membrane causes an increased glomerular permeability, resulting in the loss of albumin and other plasma proteins in the urine.

Urinary protein losses greater than 3-3.5 grams per day usually indicate nephrotic syndrome.

The loss of albumin leads to edema.

Low albumin levels also trigger cholesterol and lipoprotein synthesis in the liver, resulting in hyperlipidemia.

Q: Will you advice an increase in protein intake in these patients?

Protein: High-protein diets are not recommended as

they may encourage damage to the nephrons, leading to a progression of renal insufficiency.

Since albumin losses in nephrotic patients are due to increased catabolism, rather than a reduction in protein synthesis, low-protein diets, which decrease catabolism, may be more beneficial.

Acute Renal Failure

Acute renal failure, manifested by oliguria or anuria, usually occurs suddenly and is often reversible. It is marked by a reduction in the glomerular filtration rate and a modification in the kidneys ability to excrete metabolic wastes.

Its causes can be prerenal, intrinsic, and postrenal.

– Prerenal causes include severe dehydration and circulatory collapse.

– Causes intrinsic to the kidney include acute tubular necrosis, nephrotoxicity, vascular disorders, and acute glomerulonephritis.

– Obstructive (postrenal) causes include benign prostatic hypertrophy and bladder or prostate cancer.

Diet in Acute Renal Failure

Protein: A low-protein diet (0.5-0.6 grams per kilogram) is recommended initially. Protein may be increased in the diet as the glomerular filtration rate increases to normal.

• If dialysis is initiated, the protein level may be increased to 1.0-1.5 grams per kilogram per day if necessary to compensate for protein losses in the dialysate.

Diet in Acute Renal Failure

Calories: Calorie needs are generally elevated (35-50 kilocalories per kilogram) in order to provide positive nitrogen balance under stressful conditions. As protein is usually quite restricted, calorie needs may be met by providing greater amounts of carbohydrate and fat in the diet.

Sodium and Fluid: Sodium is restricted depending on urinary excretion, edema, serum sodium levels, and dialysis needs.

• During the oliguric phase, sodium may be restricted to 500-1000 milligrams per day, and fluid requirements are based on replacing losses via urine, vomitus, and diarrhea, plus approximately 500 milliliters per day.

Potassium: Potassium requirements vary depending on hemodynamic status and the degree of hypermetabolism due to stress, infection, or fever.

• High potassium levels are treated by dialysis or with kayexalate, an exchange resin which substitutes sodium for potassium in the gastrointestinal tract.

• During the oliguric phase, potassium may be restricted to 1,000 milligrams per day.

Chronic Renal Failure

• Approximately 90 percent of cases of end-stage renal disease are attributable to diabetes mellitus, glomerulonephritis, or hypertension.

• Kidney failure results in fluid and electrolyte imbalances, the build up of nitrogenous wastes, and reduced ability to produce renal hormones.

• The two treatment options are trans-plantation or dialysis.

• Mild renal insufficiency is defined as 40-80 percent of renal function.

• Moderate insufficiency is defined as 15-40 percent, and

• severe renal insufficiency is below these figures.

Diet in Chronic Renal Failure

• Low-protein diets may slow the progression of mild and moderate renal insufficiency.

• Therapeutic diets using plant sources of protein are more effective in delaying the progression of renal insufficiency, compared to those using animal proteins.

• Vegan (pure vegetarian) diets have been shown to provide adequate protein.

Dialysis Patients

• Dialysis changes dietary needs. Patients undergoing typical hemodialysis, involving about three treatments per week, follow diets that are restricted in protein, sodium, potassium, phosphorus, and fluid.

• Patients on continuous ambulatory peritoneal dialysis, involving several dialysate exchanges per day, can be more liberal in protein, sodium, potassium, and fluid intake.

Sodium: Sodium intake must be modified to prevent hypertension, congestive heart failure, and pulmonary edema. Limiting intake will help avoid thirst and maintain acceptable fluid balance.

Fluid: Fluid consumption should be controlled to avoid congestive heart failure, pulmonary edema, hypertension, and swelling of the legs and feet. Fluid allowances are 1,000-1,5000 milliliters per day and are based on urine output and type of dialysis.

Protein: Protein requirements range from 1.1-1.5 grams per kilogram, depending on the type of dialysis used and the patient’s nutritional status. It is important to ensure sufficient protein to maintain visceral protein stores, but to avoid excesses that could lead the accumulation of nitrogenous waste products in the blood (uremia).

Phosphorus: Kidney failure causes high levels of phosphorus to build up in the blood and disrupts calcium/phosphorus balance.

• Elevated phosphorus levels can lead to metastatic calcification (soft tissue calcification), secondary hyperpara-thyroidism, and renal osteodystrophy.

Renal osteodystrophy.

• Diseases of bone in which there is failure of normal development or abnormal metabolism in bone which is already mature.

• Principal clinical signs are distortion and enlargement of bones, susceptibility to fracture, and abnormalities of gait and posture

Potassium: Potassium restrictions depend on serum potassium levels, the type of dialysis, medications, and residual renal function. Patients on hemodialysis are usually restricted to 2,000-3,000 milligrams per day to prevent hyperkalemia between treatments.

• Patients on peritoneal dialysis may follow a more liberal dietary potassium intake, as potassium is lost in the dialysate solution during daily exchanges.

Kidney Stones

• About 12 percent of Americans develop a kidney stone at some point in their lives. Stones usually result from the crystallization of calcium (which originally came in foods or supplements) and oxalate, a part of many plant foods.

• Some people have a tendency to lose excessive amounts of calcium or oxalate through their kidneys, and they have a greater likelihood of a stone.

• Kidney stones can also form from uric acid, which is a breakdown product of protein, or from struvite (ammonio-magnesium phosphate) or cystine.

• Nutritional steps are important in preventing stones and can also help prevent recurrences, which is important given that 30-50 percent of people diagnosed with a renal stone have a recurrence within five years.

• Preventing stones is like keeping a salt crystal from forming in a glass of salty water.

• You can either reduce the concentration of salt or add more water.

• Epidemiologic studies have shown that certain parts of the diet help reduce the amount of calcium that filters into the urine.

• It is a simple matter to put these factors to work clinically.

WHAT’S IN A STONE?

• Calcium oxalate 72%

• Uric acid 23%

• Ammoniomagnesium phosphate

(struvite) 5%

• Cystine <1%

• The prevalence of kidney stones is three times higher in men than women, and is higher among Caucasians than Asians or African Americans, for reasons that are not clear.

• They are especially likely to strike between the ages of 40 and 60.

Protective FoodsWater. • Water dilutes the urine and keeps calcium,

oxalates, and uric acid in solution. In research studies, those subjects whose total fluid intake (from all sources) over 24 hours was roughly 2.5 liters, the risk of a stone was about one-third less than that of subjects drinking only half that much.

• (They do not need to drink 2.5 liters of water per day; rather this is the total fluid consumption, including juices, soups, etc.)

High-Potassium Foods. A study of 46,000 men conducted by Harvard University researchers found that a high potassium intake can cut the risk of kidney stones in half.

• Potassium helps the kidneys retain calcium, rather than sending it out into the urine.

• Potassium supplements are not generally necessary. Rather, a diet including regular servings of fruits, vegetables, and beans supplies plenty of potassium.

Calcium. Although most stones contain calcium, the calcium in foods does not necessarily contribute to stones.

• Calcium supplements taken between meals may increase the risk of stones, because about 8 percent of any extra dietary calcium passes into the urine.

• On the other hand, calcium consumed with meals has the opposite effect, reducing the risk of stones.

• The reason, apparently, is that calcium binds to oxalates in foods and holds them in the digestive tract, rather than allowing them to be absorbed.

Caffeine. Caffeinated beverages reduce the risk of stones. Caffeine’s diuretic effect causes the loss of both water and calcium, but the water loss is apparently the predominant effect. Similarly, alcoholic beverages are associated with a reduced risk of kidney stones, again presumably due to a diuretic effect. This is not a compelling reason to drink either coffee or alcohol, but their diuretic actions do present this advantage.

Problem Foods

Animal Protein.

Animal proteins cause calcium to be leached from the bones and excreted in the urine where it can form stones. Diets rich in animal proteins also increase uric acid excretion.

A modest increase in animal protein intake, from less than 50 grams to 77 grams per day, was associated with a 33 percent increased risk of stone formation.

• Between 1958 and the late 1960s, there was a sharp increase in the incidence of kidney stones in Great Britain.

• During that period, there was no substantial change in the amount of calcium or oxalate-containing foods consumed. However, the consumption of vegetables decreased, and the use of poultry, fish, and red meat increased. Statistical analyses showed a strong relationship between the incidence of stones and animal protein consumption.

Sodium. Sodium increases the passage of calcium through the kidney and increases the risk of stones. When people cut their salt (sodium chloride) intake in half, they reduce their daily need for calcium by about 160 milligrams.

• Plants of any kind—grains, vegetables, legumes, and fruits—contain almost no sodium at all unless it is added during canning or other processing.

• Dairy products and meats contain more salt than plant products, and table salt, frozen meals, and canned and snack foods are the highest-sodium food products.

Sugar.

Sugar accelerates calcium losses through the kidney. In the Nurses’ Health Study, those who consumed, on average, 60 grams or more of sugar (sucrose) per day had a 50 percent higher risk of stones than those who consumed only about 20 grams.

Climate. Kidney stones are also more common in warm climates, presumably because perspiration leads to dehydration and a more concentrated urine, and because sunlight increases the production of vitamin D in the skin which, in turn, increases calcium absorption from the digestive tract.

• Surprisingly, oxalate-rich foods, such as chocolate, nuts, tea, and spinach, are not associated with a higher risk of renal stones,

Helping Patients Avoid Kidney Stones

• Encourage patients to drink plenty of water or other fluids, staying ahead of their thirst.

• Diets including generous amounts of vegetables, fruits, and beans are rich in potassium and very low in sodium.

Helping Patients Avoid Kidney Stones, cont’n

• If you prescribe calcium supplements, encourage patients to take them with meals, rather than between meals.

• Encourage patients to avoid animal products. Their proteins and sodium content increase the risk of stones.

• Patients should keep salt and sugar use modest.

What foods are high in protein?

• meat (beef, chicken, pork, turkey)

• fish

• seafood (shrimp, scallops, clams, oysters)

• eggs

• dairy products (milk, cheese, ice cream, yogurt, pudding)

What foods are high in potassium?Most foods contain some amount of potassium.

bananas

prunes

oranges

potatoes

orange juice

sweet potatoes

grapefruit juice

tomato sauce

cantaloupe

What foods are high in phosphorus?

• The following foods are high in phosphorous and should be restricted.

• Dairy products, including:

– milk (all kinds: whole, low-fat, skim, chocolate, and buttermilk)

– cheeses (all except cream cheese)

– puddings and custards

– yogurt

– ice cream

Foods high in sodium:• canned foods (vegetables, meats, pasta

meals)• processed foods (meats such as bologna,

pepperoni, salami, hot dogs, sausage)• cheese• dried pasta and rice mixes• soups (canned and dried)• snack foods (chips, popcorn, pretzels,

cheese puffs, salted nuts, etc.)• dips, sauces, and salad dressings

• meats, chicken, turkey, and fish (especially organ meats)

• dried beans and peas, including:– black-eyes– field peas– kidney– navy– northern– pinto– lima

• nuts (all kinds and peanut butter)• seeds, bran, and whole grain cereals and breads

DONE!!