Protein intake impacts on kidney health

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By Laura Rokosz, PhD

As integrative practitioners, most of us know the standard American diet is high in sugar, salt, and fat, but for some patients, it may also be high in protein, too. With agricultural advancements and convenience foods making animal protein consumption at every meal possible, many patients are eating more protein than ever before. While it’s largely understood that sugar, salt, and fat have impacted both heart health and our waistlines, the adverse effects of the overconsumption of protein have yet to be widely acknowledged.

Dietary protein is a critical macronutrient since it is the only type of food that can be converted to muscle. Protein is the main component of muscles, bones, organs, skin, and nails. Excluding water, muscles are composed of about 80 percent protein.

The building blocks of proteins are amino acids. Unlike glucose and fatty acids, amino acids contain nitrogen. Amino acids can be used to make glucose when glucose is limited or converted to fatty acids during caloric excess. Carbohydrates and fats, on the other hand, cannot be converted to amino acids because they lack nitrogen.

The main route of elimination of nitrogen from proteins is by converting it to urea and subsequently excreting it in the urine. Diets that are high in protein place excessive burden on the kidneys to remove urea and other protein degradation products. Over time, this may lead to reduced kidney function. As a result, reduced protein consumption is recommended for those suffering from chronic kidney disease (CKD).

The recommended dietary intake of protein for healthy people is 0.8 grams per kilogram of body weight. According to the 2020 Kidney Disease Outcome Quality Initiative (KDOQI) Clinical Practice Guideline for Nutrition in CKD, this recommendation should be reduced to 0.55 to 0.60 grams of protein per kilogram of body weight per day, or to 0.28 to 0.43 grams of dietary protein per kilogram of body weight per day with additional keto acid and amino acid analogs for adults with CKD stages 3 to 5 who are metabolically stable. These restrictions may be relaxed to 0.6 to 0.8 grams of protein per kilogram of body weight per day for diabetic kidney disease (DKD) patients not on dialysis and 1.0 to 1.2 grams of protein per kilogram of body weight per day for end stage renal disease patients on dialysis. The purpose for the increased recommendations is to avoid protein energy wasting (PEW), a common occurrence in more critical care patient populations.

The quandary for most of these patients is how to keep track of protein consumption. Although this can be done with just about any calorie tracking app, the general estimates, which can be found in full here, work just as well:

Animal sources have considerably more protein than plant-based sources. They also have higher levels of phosphorous and potassium, which are minerals that must be cleared by the kidneys as well. Elevated potassium or hyperkalemia can lead to deadly changes in heart rhythm. Elevated phosphorous or hyperphosphatemia can lead to soft tissue calcification. Many plant-based foods are also high in potassium and phosphorous, but absorption of these minerals differs from that of animal-based sources.

For example, potassium rich foods that are also high in carbohydrates may impact serum potassium to a lesser degree than foods that are high in potassium and low in carbohydrates. Organic phosphorus in plant-based foods is mostly in the storage form of phytates or phytic acid and humans do not possess the enzyme required to degrade phytates or phytic acid. Thus, the bioavailability of phosphorus from plant-based sources is less than 50 percent due to the phytic acid content.

The following is a low protein menu, 0.6 grams per kilogram of body weight, for a 75-kilogram CKD patient, stage 3-5, not on dialysis, which also meets the allowance for potassium at less than 2,000 milligrams and phosphorus at 800 to 1,000 milligrams.

Breakfast: 2 tablespoons cottage cheese, 2 tablespooons plain yogurt, 1 cup mixed berries, mushroom and red pepper omelet, 2 slices low sodium toast, 8 ounces almond milk, black coffee

Lunch: Turkey sandwich with 2 slices low sodium toast, 3 ounces low sodium turkey breast, and 1 teaspoon mustard, ½ cup coleslaw

Snack: 1 medium apple, 1 tablespoon nut butter

Dinner: 3 ounces extra firm tofu made with nigari, 1 cup romaine lettuce, 1 tablespoon oil and vinegar, 1 cup broccoli, 1 cup white rice

Snack: 1 graham cracker, 1 tablespoon orange marmalade, 1 cup decaffeinated tea

Evidence suggesting that low protein diets preserve kidney function is limited. According to the American Society for Parenteral and Enteral Nutrition Clinical Guidelines, low protein diets, 0.55 to 0.60 grams per kilogram of body weight, offer little benefit in preserving kidney function as measured by glomerular filtration rate (GFR). Nonetheless, protein restriction had a beneficial effect on death and progression to end stage kidney disease (ESKD). Although effects on phosphate serum levels were mixed an improvement in serum lipid profile was noted. The 2020 KDOQI Clinical Practice Guideline for Nutrition in CKD reported mixed results on survival or renal death following a very low protein diet of 0.28 to 0.43 grams of protein per kilogram of body weight per day supplemented with keto acids, but kidney function was preserved with improved measures of bone health—lower serum phosphate and increased serum calcium.

Randomized controlled trials (RCTs) are challenging to draw conclusions from because food and genetics are such complex variables. Factoring in protein type, plant versus animal, further complicates the analysis. Reducing protein from animal sources and moving toward more vegetable protein sources, which are more alkaline, may reduce acid production and, subsequently, metabolic acidosis. Plant proteins have the added benefit of reduced phosphorous absorption, as mentioned previously. To date, there is insufficient evidence to recommend a particular protein type for CKD patients. Although preclinical studies have demonstrated that vegetable protein diets in rodent retard the development and progression of CDK conclusive evidence from RCTs is lacking.

Despite such nebulous results, I have obtained positive results following variations of the low protein diet described above in multiple patients with CKD. These results included reduced hyperfiltration and subsequent increase in GFR with reduced serum potassium and phosphate. Such restrictive dieting is no easy task as it requires extreme discipline and willpower. Since proteins are complex, they take longer to digest and therefore, provide excellent satiety. A diet with a higher percentage of carbohydrates will be rapidly metabolized and may contribute to high blood sugar levels, which poses a conundrum for DKD patients.

Patients who commit to a low protein diet should work closely with a licensed dietitian to ensure that they are meeting energy intake guidelines. As CKD progresses, the risk of PEW increases, which warrants protein supplementation with formulas that are specially designed for renal patients. Further clinical efforts to validate the benefits of a low protein or vegetable protein diet in CDK are greatly needed. In theory, this should be an ideal strategy to preserve kidney function. Adequately powered long-term RCTs that eliminate or greatly minimize confounding lifestyle variables will produce less ambiguous results.

References

Brown, R. O. and Compher, C. (2010) American Society for Parenteral and Enteral Nutrition Clinical Guidelines: Nutrition Support in Adult Acute and Chronic Renal Failure. Journal of Parenteral and Enteral Nutrition. Retrieved from: https://pubmed.ncbi.nlm.nih.gov/20631382/

Ikizler, T.A., Burrowes, J.D., Byham-Gray, L.D., Campbell, K.L., Carrero, J.-J., Chan, W., Fouque, D., Friedman, A.N. Ghaddar, S., Goldstein-Fuchs, D.J., Kaysen, G.A., Kopple, J.D., Teta, D., Yee-Moon Wang, A., and Cuppari, L. (2020) Kidney Disease Outcome Quality Initiative Clinical Practice Guideline for Nutrition in CKD: 2020 Update. American Journal of Kidney Disease. Retrieved from: https://pubmed.ncbi.nlm.nih.gov/32829751/

Palmer, B.F., Colbert, G., and Clegg, D.J. (2020) Potassium Homeostasis, Chronic Kidney Disease, and the Plant-Enriched Diets. Kidney360. Retrieved from: https://kidney360.asnjournals.org/content/kidney360/early/2019/12/04/KID.0000222019.full.pdf