By: Ana Garcia, CSUN Dietetic Intern Cohort 2021-2022
Healthy kidneys are essential to our well-being since their function is to keep our body in balance by regulating and removing substances, such as minerals, electrolytes, (e.g., calcium, potassium, sodium), acids, and protein in the blood as needed.1 The kidneys also function to produce erythropoietin (a hormone needed to make red blood cells) and turn vitamin D into its active form so it is usable in the body. Kidneys regulate fluid with a million filtering units called nephrons. Each nephron has a filter known as the glomerulus.2 To know how well our kidneys are functioning, a lab test would measure our glomerular filtration rate (GFR). A GFR consistently below normal is a cause for concern because it indicates that the kidneys cannot properly remove waste products such as ammonia, urea, uric acid, and creatinine from our blood.3 If waste cannot be excreted in the urine, these toxins build up in our body.3 Chronic kidney disease (CKD) is the gradual loss of kidney function and is diagnosed when GFR is <60.3 People with CKD must adhere to strict dietary recommendations to prevent further kidney damage and limit waste buildup in the body.
Unfortunately, most people do not know they have kidney disease until kidney damage is advanced. Approximately 15% of the population in the U.S. has kidney disease.1 That is 1 in 7 adults.1 Signs of poor kidney function include decreased urine output, fluid retention leading to edema (i.e., swelling in the legs, ankles, or feet), proteinuria (i.e., higher levels of protein in the urine), irregular heartbeat, and muscle weakness.4 People with decreasing GFR may first notice the following symptoms: nausea and vomiting, loss of appetite, shortness of breath, trouble sleeping, high blood pressure, muscle cramps, and blood in the urine.5
You are now probably wondering what can cause CKD and lead to such a lengthy list of symptoms and consequences. The two major causes for kidney disease are uncontrolled diabetes (either type 1 or 2) and uncontrolled hypertension, both of which could be prevented with a healthy lifestyle and diet.6 Other common causes of kidney damage include physical injury (e.g., heavy metal poisoning) and genetic disorders (e.g., polycystic disease, nephritis). Additionally, more than 24% of CKD cases are caused by nutrition factors.7 Research has shown that following a typical Western diet high in heavily processed foods, sodium, potassium, and phosphorus additives increases risk for developing kidney disease.1,7
How Does a Renal Diet Differ From a Regular Diet?
The difference between a renal diet and a regular diet is that a regular diet has no restrictions and can include a wide range of various fruits, vegetables, dairy, protein, and fats. Meanwhile, a renal diet limits foods high in potassium, phosphorus, sodium, and protein to prevent further kidney damage and buildup of waste. Renal diets are recommended only for individuals with kidney disease.2 Foods that are typically considered healthy can negatively impact those with kidney damage.4 Along with proper exercise and adherence to prescribed medications/supplements, a renal diet may prevent the progression of kidney disease by providing nutrient and fluid balance.3-5, 8
Note that a renal diet will differ for those on dialysis. Dialysis is needed at end stage renal failure when the kidneys are no longer working (GFR is less than 15) and have completely shut down. Because dialysis acts like a filtration system and removes protein waste from the blood, a low protein diet is not required.
How Does Protein, Potassium, and Phosphorus Consumption Impact the Kidney?
Excessive protein intake is not ideal since it can cause intraglomerular hypertension (i.e., high blood pressure and stress in the kidneys), which may result in kidney hyperfiltration, glomerular injury, and proteinuria.8 Consuming too much protein may result in a loss of kidney function over time and worsen the already decreased function of those who have CKD. Most Americans consume about 1.2-1.4 grams of protein per kg of body weight each day, which almost doubles recommended intake.9 U.S. Dietary guidelines suggest 0.8 grams of protein per kg of body weight for those on regular diets and 0.6 grams of protein per kg of body weight for those with CKD but not on dialysis.9 Research has shown that animal protein causes more strain on the kidneys than non-animal protein foods such as beans, nuts, grains, and cereals.10 An additional reason to limit protein intake is because protein contains phosphate (phosphorous).
Phosphorus is another nutrient to limit when following a renal diet. Serum phosphorus levels increase at the same rate as GFR decreases.11 More than 99% of excess phosphorus is excreted in the urine.5 However, damaged kidneys cannot remove phosphorus very well from the blood. Phosphate in the blood then binds to calcium. In order to maintain an electrolyte balance, bones will release more calcium into the blood but bones will become weaker in the process.12 High levels of phosphorus and calcium in the blood lead to calcified kidney and vessels, causing damage to the structures.1 A lower phosphorus intake has shown to reduce proteinuria.13 Although the recommended amount of phosphorus in a renal diet is less than 1000 mg per day, phosphorus recommendations are dependent on one’s lab levels.
Potassium is also a nutrient of concern since the kidneys regulate the blood’s potassium levels.13 Potassium controls the electrical signals of the myocardium (i.e., heart muscle) so the heart can beat at the right pace and so nerves can properly communicate.13 When the kidneys are not working properly, even moderate to high potassium intake may cause a buildup of potassium in the blood, known as hyperkalemia. Symptoms of hyperkalemia include irregular heartbeat, severe muscle weakness, paralysis, or even sudden death.14 Potassium blood levels should be checked regularly (annually for non-CKD patients and much more often for CKD patients) by your physician. Foods with more than 250 mg of potassium per serving are considered high potassium foods while low potassium foods have <150 mg/serving.15
|High Potassium Foods||Low Potassium Foods|
|Dairy products (Milk, yogurt ,cheese)||Arugula|
Some high potassium foods are healthy for the general population but should be limited by those with CKD, especially if potassium levels were high at the last lab check. Potassium recommendations may be individualized to keep serum potassium within a normal range.
The recommended amount of sodium on a renal diet is <2000 mg of sodium per day.15 Kidney disease is very salt sensitive due to sodium’s ability to increase fluid volume and blood pressure. When individuals with kidney disease consume excess sodium they are more likely to become thirsty, drink more liquids, and have fluid overload (e.g. edema). Consuming less sodium will lower blood pressure and proteinuria.13 To know how much sodium is in food, check the nutrition label and choose foods with less than 140 mg of sodium per serving. Another tip is to cook food at home due to the many sodium, potassium, and phosphorus additives that are found in processed and store-bought foods.15
Schedule an Appointment for Your Kidney Health
Renal diets may be different for every individual. Consider making an appointment with a Registered Dietitian at the Marilyn Magaram Center to create a meal guide that’s best for your health! Also remember to ask your primary provider to check your labs as needed.
Visit the following websites to find kidney friendly recipes and nutrition information:
- Kramer H. Kidney Disease and the Westernization and Industrialization of Food. Am J Kidney Dis. 2017;70(1):111-121. doi:10.1053/j.ajkd.2016.11.012
- Inker LA, Titan S. Measurement and Estimation of GFR for Use in Clinical Practice: Core Curriculum 2021. Am J Kidney Dis. 2021;78(5):736-749. doi:10.1053/j.ajkd.2021.04.016
- Lin J, Fung TT, Hu FB, Curhan GC. Association of dietary patterns with albuminuria and kidney function decline in older white women: a subgroup analysis from the Nurses’ Health Study. Am J Kidney Dis. 2011;57(2):245-254. doi:10.1053/j.ajkd.2010.09.027
- National Institutes of Health: National Institute of Diabetes and Digestive and Kidney Disease. Kidney Disease. https://www.niddk.nih.gov/health-information/kidney-disease/kidneys-how-they-work. Accessed November 20, 2022.
- Mahan L, Raymond J. Krause’s Food & the Nutrition Care Process. 14th ed. St. Louis, MO: 2017.
- United States Renal Data System. 2018 USRDS Annual Data Report: cardiovascular disease in patients with CKD [Internet] National Institutes of Health, National Institute of Diabetes and Digestive and Kidney Disease. Bethesda (MD). 2018. Available from: https://www.usrds.org.
- Wang Y, Chen X, Song Y, Caballero B, Cheskin LJ. Association between obesity and kidney disease: a systematic review and meta-analysis. Kidney Int. 2008;73(1):19-33. doi:10.1038/sj.ki.5002586
- Ko GJ, Rhee CM, Kalantar-Zadeh K, Joshi S. The Effects of High-Protein Diets on Kidney Health and Longevity. J Am Soc Nephrol. 2020;31(8):1667-1679. doi:10.1681/ASN.2020010028
- 9. Lin J, Fung TT, Hu FB, Curhan GC. Association of dietary patterns with albuminuria and kidney function decline in older white women: a subgroup analysis from the Nurses’ Health Study. Am J Kidney Dis. 2011;57(2):245-254. doi:10.1053/j.ajkd.2010.09.027
- Landau D, Rabkin R. Effect of nutritional status and changes in protein intake on renal function. In: Kopple JD, Massry SG, Kalantar-Zadeh K, editors. Nutritional management of renal disease. 3rd ed Amsterdam: Elsevier; 2012. pp. 197–207.
- Nishi T, Shuto E, Ogawa M, et al. Excessive dietary phosphorus intake impairs endothelial function in young healthy men: a time- and dose-dependent study. J Med Invest. 2015;62(3-4):167-172. doi:10.2152/jmi.62.167
- Chang AR, Anderson C. Dietary Phosphorus Intake and the Kidney. Annu Rev Nutr. 2017;37:321-346. doi:10.1146/annurev-nutr-071816-064607
- Naber T, Purohit S. Chronic Kidney Disease: Role of Diet for a Reduction in the Severity of the Disease. Nutrients. 2021;13(9):3277. Published 2021 Sep 19. doi:10.3390/nu13093277
- Palmer BF. Potassium Binders for Hyperkalemia in Chronic Kidney Disease-Diet, Renin-Angiotensin-Aldosterone System Inhibitor Therapy, and Hemodialysis. Mayo Clin Proc. 2020;95(2):339-354. doi:10.1016/j.mayocp.2019.05.019
- Nutrition Care Manual. Eatright.org. https://www.nutritioncaremanual.org/client_ed.cfm?ncm_client_ed_id=153