When you eat a high-protein food, such as steak, the food gets digested in your stomach and intestines. Nutrients are absorbed into your bloodstream and wastes are excreted in the feces. The kidneys help balance the levels of nutrients in the blood by removing excess potassium and phosphorus, while retaining others such as protein.
Blood Filtration
In addition to waste products produced by digestion, the body also produces waste products through normal biochemical activities such as building and breaking down muscle. The kidneys have millions of tiny filters called glomeruli that remove all these waste products from the blood. The glomeruli filter the blood, remove waste and excrete it into the urine.
Filtration Problem
In addition to removing wastes, the glomeruli act as a barrier, preventing proteins from escaping from the blood into the urine. Patients with kidney disease often have inflamed or damaged kidneys, which are less able to keep protein in the blood. Proteins pass through the glomeruli and into the urine.
Protein Loss
When kidney patients consume high-protein foods, the protein lost into the urine, causes high urine protein. This condition is called proteinuria, or urine albumin. The lost proteins include enzymes and immunoglobulins that fight disease. Patients who lose more than 3 g of protein in a 24-hour period are said to be nephrotic.
Low-Protein Diet
Proteins are much larger than molecules that usually pass through the glomeruli. Consequently, they can damage the glomeruli. High urine protein accelerates the rate of progression of kidney disease by causing needless wear and tear. The National Kidney Foundation recommends that patient with diabetes and those with chronic kidney disease consume a low protein diet to slow down the progression of disease.
Warning
Even though filtering high-protein foods can accelerate kidney disease, patients should never start a low-protein diet without consulting their nephrologists first. A low-protein diet is not the right approach for all kidney patients. For example, nephrologists advise patients on dialysis who suffer from muscle wasting to eat high-protein diets. Your nephrologist can tell you whether a low-protein diet is appropriate and how much protein you can safely eat.
References
- National Kidney Foundation; KDOQI Clinical Practice Guidelines for Chronic Kidney Disease: Evaluation, Classification, and Stratification; 2002
- National Institute for Diabetes and Digestive and Kidney Diseases; Proteinuria; March 2009
- National Kidney Foundation: Phosphorus and your CKD Diet
- National Kidney Foundation: Potassium and your CKD Diet
- DaVita; Protein and Your Peritoneal Dialysis Diet
