Your kidneys filter your blood, and produce urine from extra fluid and waste products. The glomerular filtration rate (GFR), calculated using the creatinine blood test, is a measure of how well your kidneys filter your blood. According to the National Institute of Diabetes and Digestive and Kidney Disorders, chronic kidney disease (CKD) is suspected when GFR drops below 60, and a value of 15 or less signifies kidney failure. Since the serum creatinine -- thus the GFR -- can be influenced by hydration and other factors, your doctor needs to evaluate the reason for your abnormal result. If related to CKD, changes to your diet may help improve or slow decline of your GFR and lessen your risk of kidney failure.
Dietary Protein and GFR
Because of protein’s potential to impact creatinine and estimated GFR, a restriction of dietary protein is a common recommendation in CKD. As the body turns dietary protein into amino acids, and as the body breaks down the muscle component creatine -- which is also found in meat -- creatinine is formed. Thus, consuming protein can cause at least a temporary, dose-dependent increase in GFR, although the long-term significance of this is still unclear.
A September 2005 review published in “Nutrition and Metabolism” concluded that a high protein diet does not worsen GFR in people with normal kidney function. However, in people with preexisting kidney disease, protein intake seems to matter. A review published in the January 2013 issue of “Blood Purification” concluded that a reduced protein diet slows the natural progression of kidney disease -- and slows the decline in GFR. However, eating a low or moderate amount of protein instead of excessive meat, poultry, eggs, fish, cheese and milk does not promise to improve GFR. If you have a reduced GFR, your doctor can refer you to a dietitian who specializes in kidney disease so that you understand your specific protein guidelines.
A review article published in the November 2014 issue of “European Journal of Clinical Nutrition” concluded that dietary fiber supplementation reduced -- or improved -- serum creatinine levels. Since GFR is calculated using the creatinine, a reduction in creatinine leads to an improved or higher GFR. The authors of this review proposed that fiber may help in the gut breakdown of creatinine -- before it reaches the kidneys. High fiber foods include whole grains, beans, nuts, seeds, fruit and vegetables. Many high fiber foods are naturally high in phosphorus and potassium, which are nutrients that may need to be restricted in advanced stages of CKD. So be sure to discuss your nutrition needs with your doctor and dietitian.
Management of Other Conditions
The most effective way to slow the progression of kidney disease is to control any conditions that are contributing to the kidney damage. Obesity is a known risk factor for CKD, and an October 2013 review published in “Nephrology Dialysis Transplantation” linked weight loss to an improve in GFR. Also, high blood pressure, elevated blood sugar and abnormal cholesterol levels can cause kidney damage, and although controlling these conditions may not improve GFR, controlling blood pressure, cholesterol and diabetes can slow the progression of kidney disease and slow the decline of GFR levels.
Putting It All Together
Choose a balance of healthy foods for optimal health, including fruit, vegetables, grains, protein foods including fish, soy, lean meat, beans and calcium-rich foods such as milk or fortified soy or almond milk. Limit salt and high sodium foods to help improve your blood pressure and help avoid fluid retention. If your CKD worsens and leads to abnormal blood levels of potassium or phosphorus, you may be advised to restrict these nutrients in your diet. In advanced CKD, fluid may even need to be restricted. It’s essential to discuss these restrictions with your dietitian, as the kidney diet can be complex and pose challenges to meeting your nutrition needs.
Warnings and Precautions
If you have an decreased GFR, discuss the significance and treatment plan with your doctor. Abnormal GFR can be caused by anything that increases creatinine levels -- dehydration, certain medications, intense exercise or even the use of creatine supplements. If the decreased GFR is related to CKD, your doctor can provide personalized diet recommendations, and refer you to a dietitian who specializes in kidney disease. Typical recommendations in CKD including avoiding excess protein, limiting sodium, increasing fiber intake and slowly losing weight, if overweight. Your dietitian can help ensure your diet is geared towards improving kidney function -- or at least slowing decline in function, managing your other health conditions and ensuring all nutrient needs are met.
Reviewed by: Kay Peck, MPH, RD