Understanding CKD Diet Recommendations
Content by: Jamie Rinaldi RD LD
Chronic kidney disease encompasses multiple kidney abnormalities, which equates to a number of diet restrictions and nutrition recommendations. Follow along the slides presentation...
Chronic kidney disease encompasses multiple kidney abnormalities, whether one or more are present, resulting in decreased renal function for three months or longer. One of the most important jobs of the kidneys is to filter waste products from the blood. The glomerulus, consisting of a cluster of tiny capillaries, is the part of the kidney that performs this filtration process. The glomerular filtration rate (GFR) reflects the rate at which kidneys filter the blood, indicating the stage of chronic kidney disease (CKD), and it is calculated using creatinine (Cr). Cr is a byproduct of creatine metabolism. GFR decreases as CKD progresses. All five stages are explained below, however this article provides nutritional guidelines only for stages one through four.
GFR (mL/min): 90 or higher
For most people, this is a normal level, however there still may be some mild kidney damage if there is protein in the urine.
GFR (mL/min): 60-89
This may indicate early kidney disease, however it may be the normal level for elderly and infants.
GFR (mL/min): 30-59
A GFR between 30 and 59 reflects moderate kidney disease.
GFR (mL/min): 15-29
This signifies severe kidney disease.
GFR (mL/min): 15 or lower
A GFR of 15 or lower is consistent with kidney failure, also known as end stage renal disease (ESRD). At this stage, dialysis or a kidney transplant is required to sustain life.
There are several key nutrients that may be restricted with CKD and diet becomes more limited as the disease progresses. These nutrients are protein, sodium, potassium, phosphorus, and fluid.
One of the byproducts of protein metabolism is ammonia, a toxin that most bodies can efficiently eliminate. It is converted to urea by the liver, then the kidneys filter it out of the blood and excrete it in urine. Excessive protein intake is detrimental to the body when renal function is impaired. The already damaged kidneys are unable to adequately eliminate urea, resulting in uremia, which is excessive urea in the blood, and azotemia, which is an overload of blood urea nitrogen (BUN) and Cr in the blood. Elevated concentrations of these byproducts of protein metabolism are poisonous to the body. The pressure of high protein intake on injured kidneys not only allows for the build-up of these toxins but also further impairs kidney function.
A low protein diet puts less pressure on the glomerulus, thereby attenuating increased damage to the kidneys and reducing potentially toxic waste products of protein metabolism in the blood. Individuals with CKD are advised to consume between 0.6 and 0.8 grams of protein per kilogram per day (0.6-0.8g/kg/day) as long as calorie needs are being met. A low protein diet with an inadequate intake of calories may lead to malnutrition and protein-energy wasting. In this case, nutritional supplementation is advised.
Sodium is a mineral occurring naturally in most foods and an electrolyte with multiple functions, including the regulations of blood volume, blood pressure, acid-base balance, muscle contraction, nerve activity, and the retention and elimination of fluid. Sodium is a vital nutrient, however it can build up to harmful levels in individuals with CKD due to reduced glomerular function. Too much sodium in the blood, hypernatremia, may cause high blood pressure, edema in the extremities and face, congestive heart failure, and shortness of breath. An appropriate intake of sodium for most CKD patients to prevent hypernatremia and its dangerous consequences is between 1500 and 2000 milligrams (mg) per day.
Potassium is another mineral and electrolyte, essential for maintaining fluid and electrolyte balance, keeping heart rate regular, and supporting proper nerve transmission and muscle contraction. Hyperkalemia, high potassium levels in the blood, ensues when the kidneys are unable to effectively flush out excess potassium via urine, and it can lead to life-threatening cardiac arrhythmias, paralysis, muscle weakness, heart attacks, and death. Potassium is generally limited to 2000 to 3000mg in those with CKD, however restrictions also depend on serum levels measured by routine blood testing.
Phosphorus is a mineral that along with calcium is critical to building strong teeth and bones. It also plays a role in muscle movement and energy storage. Healthy kidneys maintain an appropriate balance of phosphorus and calcium in the blood. The build-up of phosphorus that occurs with impaired blood filtration causes calcium to be pulled from the bones in effort to restore that balance in the blood. Bones become weak and are more prone to breaking without adequate calcium. This calcium in the blood may also bind with phosphorus and form calcium deposits that settle in the blood vessels, heart, joints, muscles, and skin, reducing blood circulation, damaging organs, and causing pain. In early kidney disease, phosphorus restriction is rarely required. As CKD progresses, 1000mg is the upper limit for consumption, and a phosphate binder may also be prescribed. This binder is taken with food and works to eliminate excess phosphorus from the digestive tract in the stool, before it can be absorbed into the blood.
Although uncommon in the early stages of CKD, in later stages and in kidney failure, fluid overload may occur as the kidneys are unable to remove excess fluid. The potential outcomes of fluid overload are high blood pressure, edema in the extremities and face, cardiac problems, and shortness of breath. The amount of fluid allotted is dependent on urine output. Most physicians will prescribe 500 to 700 milliliters (ml) above the amount of urine output to account for losses from the lungs and skin. They also may consider any weight fluctuations from day to day to determine a proper fluid prescription.
Next Step: Estimate Calorie Requirements:
35 kilocalories/kilogram (kcals/kg) for patients under 60 years of age with a normal body mass index (BMI)
30-35 kcals/kg for patients 60 years and older with a normal BMI
23-25 kcals/kg for obese patients
40-50 kcals/kg for underweight patients or those under severe stress