Eating Right for Chronic Kidney Disease Series – Balancing Protein Consumption

Protein serves as a foundational element for your body, playing a crucial role in growth, healing, and overall health. Achieving the right balance of protein is essential, as insufficient amounts can lead to weakened skin, hair, and nails, while an excess may pose problems. To optimize your well-being and vitality, it might be necessary to fine-tune your protein intake.

The appropriate amount of protein varies based on factors such as your size, activity level, and the stage of kidney disease you’re in. If you have kidney disease without undergoing dialysis, your healthcare team might advise limiting protein consumption. Diets excessively rich in protein can strain the kidneys, potentially causing more harm.

High Protein Diet and Kidney Function

High protein intake, defined as exceeding 1.2 grams of dietary protein per kilogram of body weight per day, can induce significant alterations in renal function and kidney health. Specifically, it affects kidney function, increasing pressure within the filtering units of the kidneys and raising the rate at which fluids are filtered. While short-term increases in GFR may occur, prolonged exposure to high dietary protein intake can lead to kidney damage and a decline in renal function over time.

The potentially harmful effects of elevated protein intake are not uniformly observed in individuals with normal kidney function compared to those with pre-existing kidney disorders. Studies, such as the Nurses’ Health Study, have indicated an association between high protein diet and a faster decline in estimated GFR in individuals with subnormal kidney function.

Dietary Protein Intake in North Americans with and without CKD

In the context of CKD management, a low protein diet (LPD) is often recommended, aiming for a range of 0.6–0.8 g/kg/day. Despite the potential benefits of LPD in slowing CKD progression, its adoption faces challenges in the contemporary clinical setting. Data from the National Health and Nutrition Examination Survey (NHANES) reveals a substantial gap between recommended protein intake and actual consumption in the United States, posing a hurdle to the implementation of LPD.

Potential Renal Acid Load (PRAL)

PRAL = (0.49 * protein intake in g/day) + (0.037 * phosphorus intake in mg/day) – (0.02 * potassium intake in mg/day) – (0.013 * calcium intake in mg/day) – (0.027 * magnesium intake in mg/day)

Each food item can be given a PRAL score – lower the better. PRAL scores can loosely be mapped to “acidic” or “alkaline” food items.

In general, –

  • alkaline: Fruits / vegetables / potatoes / wine / soda water (low or negative PRAL score)
  • acidic: whole grains / meats / dairy / fish / beer (high PRAL score)

The alkaline diet cannot change the pH value of our blood. Our kidneys work continuously to keep this critical value (pH) between 7.35-7.45. However, depending on our diet, the kidneys may have to work harder or less to maintain this narrow range. This is where alkaline diets or low-PRAL diets play a role on managing chronic kidney disease (CKD), based on biochemistry 101.

The kidneys play a vital role in regulating the acid–base balance by excreting hydrogen ions (H+) into the urine and absorbing bicarbonate (HCO3–) from the urine. This crucial bicarbonate reabsorption occurs primarily in the kidney, specifically in the tubular lumen and tubular epithelium. For those quick to dismiss the alkaline diet as a passing trend, it’s essential to grasp this fundamental renal biochemistry: heightened meat or protein intake puts increased pressure on our kidneys to buffer (by reabsorbing bicarbonates) to uphold pH within a narrow range.

A Low PRAL Diet (LPRALD) is essentially a LPD also, with some additional considerations.

Benefits of Protein Restriction in CKD Patients

Effect on Proteinuria and Albuminuria

Protein restriction has demonstrated remarkable efficacy in reducing nitrogen waste products and alleviating kidney workload. One notable impact is the reduction of proteinuria by 20–50% in CKD patients, with a linear relationship between decreased protein intake and reduced proteinuria.

Effect on CKD Progression

While the Modification of Diet in Renal Disease (MDRD) study initially presented inconclusive evidence on the effectiveness of LPD, secondary analyses revealed a nuanced perspective. Each 0.2 g/kg/day decrease in protein intake was associated with a modest amelioration in GFR decline and a halved risk of renal failure or death. Further studies, including meta-analyses, support the risk reduction of end-stage renal disease (ESRD) through protein restriction among non-diabetic CKD patients.

Effect on Metabolic Control

LPD demonstrates a range of metabolic advantages in CKD, including improved control of metabolic acidosis and CKD-mineral and bone disorder (MBD). LPD, especially when incorporating plant-based proteins, effectively lowers serum phosphorus, contributing to the reduction of PTH and FGF-23 levels. These metabolic benefits enhance control over uremic symptoms, decrease cardiovascular risk, and reduce the need for multiple medications.

Conservative Management with LPD in End-Stage Renal Disease

Embracing a conservative approach, LPD emerges as a valuable tool to delay the initiation of dialysis therapy, particularly in very late-stage CKD. Studies demonstrate that LPD, when supplemented appropriately, can significantly prolong the time to dialysis initiation without compromising patient outcomes. The economic benefits and time-saving aspects of delayed dialysis further underscore the advantages of LPD in managing advanced CKD.

Bicarb and LPD Diet

In patients with CKD of different aetiologies in stages 1 – 4 and 5 not yet requiring dialysis and not treated with sodium bicarbonate, the blood bicarbonate concentration shows a positive correlation with glomerular filtration rate (GFR). The first reports of beneficial effects of the combination of a low-protein diet with oral administration of sodium bicarbonate in patients with CKD were published as early as in the 1930s.

Sodium bicarbonate, commonly known as baking soda, serves as an effective alkalizing agent often utilized for GERD/indigestion. However, its high sodium content may not be suitable for everyone, particularly for individuals with Chronic Kidney Disease (CKD). A viable alternative is potassium bicarbonate. It’s crucial to consult with your GP or nephrologist since the recommended intake of potassium, bicarbonate, and phosphate varies based on the stage of kidney disease.

Interestingly, bicarbonate administration demonstrates efficacy comparable to a plant-based diet rich in fruits and vegetables in reducing the PRAL score, as indicated by research findings. In two one-year intervention studies, patients with stage 3 or 4 CKD were treated with either sodium bicarbonate or fruits and vegetables adjusted to decrease renal acid load, a hypothetical metabolic risk factor for kidney damage, by 50%.

Net Nitrogen Utilisation (NNU)

Elite athletes can teach us a few things about protein intake, including the role of ammonia in our bodies. Ammonia is produced during normal amino acid metabolism and can be toxic in high concentrations. The liver converts ammonia to urea through a process called the urea cycle. Liver dysfunction, such as cirrhosis, can lead to increased levels of ammonia in the blood (hyperammonemia). Most of the ammonia in the body is produced when bacteria in the intestines break down protein.

Amino acids provide a solution to reduce ammonia in the body. They are pre-digested protein and do not need to be broken down, thus creating no additional ammonia load for the body. Amino acids have several benefits, including reducing stress on the digestive system, providing the protein needed by the liver to remove toxins and hormones, supporting kidney function, and improving digestion, nutrient absorption, sleep quality, healing, skin and hair quality, libido, energy, and mental clarity.

When it comes to Net Nitrogen Utilisation (NNU), raw amino acids are superior to other protein sources such as plant proteins, egg whites, whey, fish, meat, poultry, whole dairy, and egg yolk.

To summarize the dietary recommendations for kidney patients and health seekers:

  • Follow a low-protein diet with a low PRAL score.
  • Consider introducing bicarbs and monitoring blood potassium levels.
  • Raw amino acid supplements can be beneficial, but it is important to consult with your nephrologist and care team before choosing a specific product.
  • Ketoanalogues, which are nitrogen-free analogs of essential amino acids, can be included in a reduced protein diet to prevent malnourishment and delay the progression of CKD. Consult with your healthcare provider for appropriate dosage and usage.

Conflicting Data and Safety Considerations

Despite the plethora of evidence supporting the benefits of LPD, debates persist due to conflicting reports and concerns about malnutrition. Notably, studies like the MDRD study showed negative results, and the efficacy of LPD in diabetic patients remains inconclusive. However, carefully monitored interventions have shown acceptable safety and low rates of malnutrition even with very low protein diets.

Frequently Asked Questions

Q1: How does high protein intake affect renal function in the long term?
A1: Prolonged exposure to high dietary protein intake can lead to kidney damage, manifested by increased intraglomerular pressure and glomerular hyperfiltration. Over time, this may contribute to the progression of chronic kidney disease (CKD).

Q2: Is there a link between proteinuria and dietary protein intake?
A2: Yes, protein restriction has been shown to significantly reduce proteinuria in CKD patients. The linear relationship between decreased protein intake and reduced proteinuria highlights the potential benefits of a low protein diet in managing CKD.

Q3: How does LPD contribute to delaying the initiation of dialysis therapy?
A3: LPD, when supplemented appropriately, can delay the initiation of dialysis therapy by relieving clinical manifestations of uremia, even in very late-stage CKD. This conservative approach offers economic benefits and preserves residual kidney function.

In conclusion, our comprehensive review underscores the nuanced relationship between dietary protein intake and chronic kidney disease. Upon initiating dialysis, there’s a likelihood that you’ll need to increase your protein intake. Dialysis treatments can result in protein loss, necessitating dietary adjustments.

For personalized guidance on your protein requirements, consult with your doctor or dietitian. A skilled dietitian can assist in creating a tailored meal plan that ensures you receive the optimal amount of protein for your specific needs.

References

  • Skiba K, Szotowska M, Kolonko A, Adamczak M, Więcek A: Prevalence of metabolic acidosis in kidney transplant patients. Transpl Int 2013; 26:S243
  • Lyon DM, Dunlop DM, Steward CP: The alkaline treatment of chronic nephritis. Lancet 1931; 2: 1009-1013.

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