Nutrition and Renal Disease

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Nutrition and Renal DiseaseThe kidneys' job is to keep the body's fluids, electrolytes, andorganicsolutes in a healthy balance. Their functional units are the millionorso nephrons in the renal cortex which filter most constituents of

theblood other than red blood cells and protein, reabsorb neededsubstances, secrete hydrogen ions to maintain acid-base balance, andsecrete wastes.1Urine formation consists of three basic processes: glomerular

filtration, tubular secretion, and tubular reabsorption. Severaldiseaseconditions can interfere with these functions. Inflammatory anddegenerative diseases can involve the small blood vessels andmembranes

in the nephrons. Urinary tract infections and kidney stones caninterfere with normal drainage, causing further infection and tissuedamage. Circulatory disorders, such as hypertension, can damage thesmall renal arteries. Other diseases, such as diabetes, gout, and

urinary tract abnormalities can lead to impaired function,infection, orobstruction. Toxic agents such as insecticides, solvents, andcertaindrugs may also harm renal tissue.Nephrotic Syndrome

In nephrotic syndrome, an injury to the glomerular basement membranecauses an increased glomerular permeability, resulting in the lossofalbumin and other plasma proteins in the urine.Urinary protein losses greater than 3-3.5 grams per day usuallyindicate nephrotic syndrome.Although albumin synthesis in the liver is increased in nephroticsyndrome, it is not enough to compensate for losses in the urine.Theloss of albumin leads to edema.

Low albumin levels also trigger cholesterol and lipoproteinsynthesis inthe liver, resulting in hyperlipidemia. At the same time, hepaticcatabolism of serum lipoproteins is reduced and urinary excretion of

HDLis increased. These lipid abnormalities can be exacerbated bymedications often used to treat nephrotic syndrome, such assteroids,diuretics, and anti-hypertensive agents.Diet for Nephrotic Syndrome

A well-planned diet can replace lost protein and ensure efficientutilization of ingested proteins through provision of adequatecalories.Dietary changes can also help control hypertension, edema, and

hyperlipidemia, and slow the progression of renal disease.Protein: High-protein diets are not recommended as they mayencouragedamage to the nephrons, leading to a progression of renalinsufficiency.

Since albumin losses in nephrotic patients are due to increasedcatabolism, rather than a reduction in protein synthesis, low-proteindiets, which decrease catabolism, may be more beneficial.2The optimal amount of dietary protein necessary to prevent protein

catabolism and progression of renal disease has not beenestablished. Acommon recommendation is 0.6 grams of protein per kilogram of idealbodyweight, adjusted depending on the glomerular filtration rate and

nutritional status, plus gram-for-gram replacement of urinaryproteinlosses.A vegetarian diet, often used for lipid-lowering, also offers aconvenient way to provide adequate, but not excessive, protein. In a

1992 study, a group of 20 nephrotic syndrome patients were put on avegetarian diet for eight weeks. Protein intake averaged 0.7 gramsperkilogram per day, which was more appropriate to their needs than the

1.15 grams per kilogram provided in their usual diet.3Sodium and Fluid: A limit on sodium of 1-3 grams per day is usuallyrecommended to control edema and hypertension.Lipids: A diet low in saturated fat and cholesterol, combined with

lossof excess weight, is recommended to reduce the risk ofcardiovasculardisease.Many clinicians recommend limiting cholesterol to less than 300milligrams per day and fat intake to 30 percent of calories.

However,research has shown that such recommendations lead to only minimallipidlowering.As noted in detail in Section 1, low-fat vegetarian diets are muchmoreeffective for lipid control and usually lead to the reversal of

atherosclerotic disease.An eight-week trial in 13 men and 7 women with hyperlipidemia andnephrotic syndrome showed that a vegetarian diet significantlyreducedcholesterol, triglycerides, and phosphorus.

Energy: Calorie intake should be adequate to achieve and maintainidealbody weight and maintain protein stores.Foods rich in " complex " carbohydrates should provide the majority ofcalories.

Supplements: Patients with nephrotic syndrome are often low in Bvitamins and zinc, and can benefit from supplements. In addition,sincea significant portion of serum calcium is protein-bound, it tends to

below when serum proteins are reduced. No modification is routinelyneededfor potassium, but potassium losses due to secondaryhyperaldosteronismmay require replacement.The following clinical values should be monitored:

Serum albumin and total proteinUrinary proteinGlomerular filtration rateDietary protein, fat, and cholesterolDaily weightsSerum lipidsAcute Renal FailureAcute renal failure, manifested by oliguria or anuria, usually

occurssuddenly and is often reversible. It is marked by a reduction in theglomerular filtration rate and a modification in the kidneys abilitytoexcrete metabolic wastes.Its causes can be prerenal, intrinsic, and postrenal. Prerenal

causesinclude severe dehydration and circulatory collapse. Causesintrinsic tothe kidney include acute tubular necrosis, nephrotoxicity, vasculardisorders, and acute glomerulonephritis. Obstructive (postrenal)

causesinclude benign prostatic hypertrophy and bladder or prostatecancer.1The most common form of intrinsic renal disease is acute tubularnecrosis, accounting for about 75 percent of cases. Acute tubular

necrosis may be due to posttraumatic or surgical shock or to thetoxiceffects of drugs, metals, or organic compounds.Nutrition strategies in acute tubular necrosis vary depending on its

stage. During phase one, oliguria, less than 400 milliliters ofurine isproduced per day. This phase usually lasts one to three weeks. Signsandsymptoms include nausea, vomiting, fluid overload, and elevation of

BUN,creatinine, phosphorus, and potassium levels. Dialysis may be neededduring this stage to reduce acidosis, control hyperkalemia, andcorrecturemia.The diuretic phase of acute tubular necrosis lasts one to two weeks,

andis characterized by increased urine output and a return of theabilityto eliminate wastes.Fluid and electrolyte balance should be monitored and replacementsmadeas necessary. The convalescent phase occurs over the next two to six

months.Diet in Acute Renal FailureDiet plays a critical role in the care of patients with acute renalfailure. Clinicians should plan diets with an eye toward thepossibilityof uremia, metabolic acidosis, fluid and electrolyte imbalances,

infection, and tissue destruction. Nutritional support of dialysiswillbe discussed below in the section on chronic renal failure.Protein: A low-protein diet (0.5-0.6 grams per kilogram) isrecommended

initially.Protein may be increased in the diet as the glomerular filtrationrateincreases to normal. If dialysis is initiated, the protein level maybeincreased to 1.0-1.5 grams per kilogram per day if necessary to

compensate for protein losses in the dialysate.Calories: Calorie needs are generally elevated (35-50 kilocaloriesperkilogram) in order to provide positive nitrogen balance understressfulconditions. As protein is usually quite restricted, calorie needs

may bemet by providing greater amounts of carbohydrate and essential fattyacid in the diet.Sodium and Fluid: Sodium is restricted depending on urinaryexcretion,edema, serum sodium levels, and dialysis needs. During the oliguric

phase, sodium may be restricted to 500-1000 milligrams per day, andfluid requirements are based on replacing losses via urine, vomitus,anddiarrhea, plus approximately 500 milliliters per day.Potassium: Potassium requirements vary depending on hemodynamic

statusand the degree of hypermetabolism due to stress, infection, orfever.High potassium levels are treated by dialysis or with kayexalate, anexchange resin which substitutes sodium for potassium in the

gastrointestinal tract. During the oliguric phase, potassium may berestricted to 1,000 milligrams per day.Chronic Renal FailureApproximately 90 percent of cases of end-stage renal disease areattributable to diabetes mellitus, glomerulonephritis, or

hypertension.Kidney failure results in fluid and electrolyte imbalances, thebuild upof nitrogenous wastes, and reduced ability to produce renalhormones.The two treatment options are transplantation or dialysis.

Mild renal insufficiency is defined as 40-80 percent of renalfunction.Moderate insufficiency is defined as 15-40 percent, and severe renalinsufficiency is below these figures.2Diet in Chronic Renal Failure

Low-protein diets may slow the progression of mild and moderaterenalinsufficiency. Therapeutic diets using " plant sources " of *protein*aremore effective in delaying the progression of renal insufficiency,

compared to those using animal proteins.Vegan (pure vegetarian) diets have been shown to provide adequateprotein.A study of 22 patients with mild renal failure compared a vegan dietto

a conventional low-protein diet.All patients were followed for at least six months.There was no sign of protein insufficiency and inorganic phosphoruslevels remained normal.Dialysis Patients

Dialysis changes dietary needs. Patients undergoing typicalhemodialysis, involving about three treatments per week, followdietsthat are restricted in protein, sodium, potassium, phosphorus, andfluid. Patients on continuous ambulatory peritoneal dialysis,

involvingseveral 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

helpavoid thirst and maintain acceptable fluid balance.Restrictions range from 1,000-3,000 milligrams per day withhemodialysisand 2,000-4,000 milligrams per day for peritoneal dialysis. Majorsalt

sources are described below.Fluid: Fluid consumption should be controlled to avoid congestiveheartfailure, pulmonary edema, hypertension, and swelling of the legs andfeet. 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 nutritionalstatus. It is important to ensure sufficient protein to maintain

visceral protein stores, but to " avoid excesses " that could lead theaccumulation of nitrogenous waste products in the blood (uremia).Phosphorus: Kidney failure causes high levels of phosphorus to build

upin the blood and disrupts calcium/phosphorus balance.Elevated phosphorus levels can lead to metastatic calcification(softtissue calcification),secondary hyperparathyroidism, and renal osteodystrophy.

Recommended intakes usually range from 800-1,000 milligrams per daywithhemodialysis and less than 1,200 milligrams per day with periotonealdialysis.Potassium: Potassium restrictions depend on serum potassium levels,

thetype of dialysis, medications, and residual renal function. Patientsonhemodialysis are usually restricted to 2,000-3,000 milligrams perday toprevent hyperkalemia between treatments.Patients on peritoneal dialysis may follow a more liberal dietary

potassium intake, as potassium is lost in the dialysate solutionduringdaily exchanges. Some high- and low-potassium foods are listed inTable1, Section 5.Kidney StonesAbout 12 percent of Americans develop a kidney stone at some point

intheir lives. Stones usually result from the crystallization ofcalcium(which originally came in foods or supplements) and oxalate, a partofmany plant foods.Some people have a tendency to lose excessive amounts of calcium or

oxalate through their kidneys, and they have a greater likelihood ofastone.Kidney stones can also form from uric acid, which is a " breakdownproduct " of protein, or from struvite (ammoniomagnesium phosphate)

orcystine.The prevalence of kidney stones is three times higher in men thanwomen,and is higher among Caucasians than Asians or African Americans, forreasons that are not clear. They are especially likely to strike

betweenthe ages of 40 and 60.Nutritional steps are important in preventing stones and can alsohelpprevent recurrences, which is important given that 30-50 percent ofpeople diagnosed with a renal stone have a recurrence within five

years.Preventing stones is like keeping a salt crystal from forming in aglassof salty water. You can either reduce the concentration of salt oraddmore 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? 7Calcium oxalate 72%Uric acid 23%Ammoniomagnesium phosphate (struvite) 5%

Cystine <1%Protective FoodsCertain parts of the diet clearly help reduce the risk. The first isnosurprise.Water. Water dilutes the urine and keeps calcium, oxalates, and uricacid in solution. In research studies, those subjects whose total

fluidintake (from all sources) over 24 hours was roughly 2.5 liters, theriskof a stone was about one-third less than that of subjects drinkingonlyhalf that much.(They do not need to drink 2.5

liters of water per day; rather thisisthe total fluid consumption, including juices, soups, etc.) Patientsneed to understand that their thirst sense can lag behind theirhydration status, and they may need to develop a routine for extra

waterconsumption.High-Potassium Foods.A study of 46,000 men conducted by Harvard University researchersfoundthat a high potassium intake can cut the risk of kidney stones inhalf.

Potassium helps the kidneys retain calcium, rather than sending itoutinto the urine. Potassium supplements are not generally necessary.Rather, a diet including regular servings of organic fruits,vegetables,

and beans supplies plenty of potassium.Calcium. Although most stones contain calcium, the calcium in foodsdoesnot 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 theurine.On the other hand, calcium consumed with meals has the oppositeeffect,reducing the risk of stones.

The reason, apparently, is that calcium " binds " to oxalates in foodsandholds them in the digestive tract, rather than allowing them to beabsorbed.Problem FoodsAnimal 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.In a controlled research study, published in the American Journal ofClinical Nutrition, research subjects on a diet eliminating animal

protein had less than half the calcium loss that they had on theirbaseline diet.The Harvard study mentioned earlier found that even a modestincrease inanimal protein, from less than 50 grams to 77 grams per day, was

associated with a 33 percent increased risk of stones in men.The same is true for women.The Nurses' Health Study, a long-term study of health factors in alargegroup of women, revealed an even greater risk of stones from animal

protein than was found in previous studies in men.The association between animal proteins and stones probably relatesbothto the amount of protein they contain and to their content of thesulfur-containing amino acids.

In particular, the sulfur in cystine and methionine is converted tosulfate, which tends to acidify the blood.As a part of the process of neutralizing this acid, bone isdissolved,and bone calcium ends up in the urine.

Meats and eggs contain two to five times more of thesesulfur-containing amino acids than are found in whole grains anddriedunprocessed beans.Between 1958 and the late 1960s, there was a sharp increase in the

incidence of kidney stones in Great Britain. During that period,therewas no substantial change in the amount of calcium or oxalate-containingfoods consumed.However, the consumption of vegetables decreased, and the use of

poultry, fish, and red meat increased.Statistical analyses showed a strong relationship between theincidenceof stones and animal protein consumption.Sodium. Sodium increases the passage of calcium through the kidney

andincreases 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 otherprocessing.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.For more information, see the sodium/potassium chart in Section 5.Sugar. Sugar accelerates calcium losses through the kidney.In the Nurses' Health Study, those who consumed, on average, 60

gramsor more of sugar (sucrose) per day had a 50 percent higher risk ofstones than those who consumed only about 20 grams.SUGAR IN COMMON FOODS (grams)Candy bar (2 ounces) 22-35Cookies (3) 11-14

Corn flakes (1 cup, 28 grams) 2Frosted corn flakes (1 cup, 41 grams) 17Crackers (5) 1Fruit cocktail (1/2 cup, 124 grams) 14Grape jam (1 tablespoon) 13Ice cream (1/2 cup, 106 grams) 21Soda (12 ounces)

40White bread (2 slices) 1Source: package informationClimate. Kidney stones are also more common in warm climates,presumablybecause perspiration leads to dehydration and a more concentrated

urine,and because sunlight increases the production of vitamin D in theskinwhich, in turn, increases calcium absorption from the digestivetract.Surprisingly, oxalate-rich foods, such as nuts, tea, and spinach,

arenot associated with a higher risk of renal stones, nor is vitamin C,even though it can be converted to oxalate.A large study of men taking vitamin C supplements found that theyhadno more kidney stones than men who do not take them.

Helping Patients Avoid Kidney StonesHere are simple steps to help your patients avoid kidney stones.Encourage patients to drink plenty of water or other fluids, stayingahead of their thirst.

Diets including generous amounts of vegetables, fruits, and beansarerich in potassium and very low in sodium.If you prescribe calcium supplements, encourage patients to takethemwith 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.Cranberry Juice: An Old Remedy Is Clinically Tested

Cranberry juice has long been used as a folk remedy for urinaryinfections. A 1994 report in the Journal of the American MedicalAssociation showed that it does indeed have at least a preventiveeffect.

In a test involving 153 elderly women in Boston, half the subjectsdrank300 milliliters (about one and one-quarter cups) of cranberry juicecocktail each day, using the bottled beverage that is commonly sold

ingrocery stores. The other subjects consumed a drink that looked andtasted like cranberry juice, but had no real juice in it.Over the next six months, urine samples were collected and testedfor

signs of bacteria. The women consuming cranberry juice had only 42percent as many urinary infections as the control group.The number of cases that had to be treated by antibiotics was alsoonlyabout half, which is a real advantage, since antibiotics can

sometimeslead to yeast infections and other problems. It takes about four toeight weeks for the preventive effect to be seen.The explanation for the effect of cranberry juice is probably not an

acidification of the urine, because the placebo drink also reducedurinary pH.Rather, cranberries contain a substance that stops bacteria frombeingable to attach to cells, and this is probably true whether the

cranberryjuice reaches the bacteria in the digestive tract or the urinarytract.Substances that interfere with bacterial adhesion have also beenfoundin blueberries, but not in orange, grapefruit, pineapple, mango, or

guavas.References1. Mahan LK, Arlin M. Krause's Food, Nutrition, and Diet Therapy.W.B.Saunders, Philadelphia, 1992.2. The American Dietetic Association. Handbook of ClinicalDietetics,second edition. Yale University Press, 1992.

3. D'Amico G, Gentile MG, Manna G, et al. Effect of vegetarian soydieton hyperlipidemia in nephrotic syndrome. Lancet 1992;339:1131-4.4. The American Dietetic Association. Manual of Clinical Dietetics,

fifth edition. American Dietetic Association, Chicago, 1996.5. Gretz N, Meisinger M, Strauch M. Does a low protein diet reallyslowdown the rate of progression of chronic renal failure? Blood Purif1989;7:33:33-8.

6. Barsotti G, Morelli E, Cupisti A, Meola M, Dani L, Giovannetti S.Alow-nitrogen, low-phosphorus vegan diet for patients with chronicrenalfailure. Nephron 1996;74:390-4.7. Curhan GC, Willett WC, Rimm EB, Stampfer MJ. A prospective study

ofdietary calcium and other nutrients and the risk of symptomatickidneystones. N Engl J Med 1993;328:833-8.8. Curhan GC, Willett WC, Rimm EB, Spiegelman D, Stampfer MJ.Prospective study of beverage use and the risk of kidney stones. Am

JEpidemiol 1996;143:240-7.9. Curhan GC, Willett WC, Speizer FE, Spiegelman D, Stampfer MJ.Comparison of dietary calcium with supplemental calcium and othernutrients as factors affecting the risk for kidney stones in women.

AnnInt Med 1997;126:497-504.10. Soucie JM, Thun MJ, Coates RJ, McClellan W, Austin H.Demographicand geographic variability of kidney stones in the United States.KidneyInt 1994;46:893-9.11. Lemann J. Composition of the diet and calcium kidney stones. N

EnglJ Med 1993;328:880-2.12. Remer T, Manz F. Estimation of the renal net acid excretion byadults consuming diets containing variable amounts of protein. Am JClinNutr 1994;59:1356-61.13. Breslau NA, Brinkley L, Hill KD, Pak CYC. Relationship of animal

protein-rich diet to kidney stone formation and calcium metabolism.JClin Endocrinol 1988;66:140-6.14. Robertson WG, Peacock M, Hodgkinson A. Dietary changes and theincidence of urinary calculi in the U.K

.. between 1958 and 1976. JChronDis 1979;32:469-76.15. Nordin BEC, Need AG, Morris HA, Horowitz M. The nature andsignificance of the relationship between urinary sodium and urinarycalcium in women. J Nutr 1993;123:1615-22.

16. Lemann J Jr, Adams ND, Gray RW. Urinary calcium excretion inhumanbeings. N Engl J Med 1979;301:535-41.17. Soucie JM, Coates RJ, McClellan W, Austin H, Thun MJ. Relationbetween geographic variability in kidney stones prevalence and risk

factors for stones. Am J Epidemiol 1996;143:487-95.18. Avorn J, Monane M, Gurwitz JH, Glynn RJ, Choodnovskiy I, LipsitzLA.Reduction of bacteriuria and pyuria after ingestion of cranberryjuice.JAMA 1994;271:751-4.

--Section Six:Nutrition and Renal Disease Study QuestionsWhat are some of the main problems of nephrotic syndrome?

Why are high protein diets not recommended with nephrotic syndrome?Whatare the alternatives?What type of dietary restrictions are used in acute renal failure?What are the treatment options for chronic renal failure? How do

dietaryregimens differ between hemodialysis and peritoneal dialysis?What steps can be taken to prevent kidney stones?_________________-- Diana Gonzalez

Nothing wastes more energy than worrying - the longer a problem is carried, the heavier it gets. Don't take things too seriously - live a life of serenity, not a life of regrets.

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