Kidneys have several functions in the human body. One is to filter the body's blood, removing wastes and excess water. Professionals use renal function to describe how efficiently the kidneys filter blood. If renal function decreases, the kidneys lose their ability to filter waste products from the blood stream. A diet high in protein causes excess protein molecules to be sent into the blood and through the kidneys, forcing them to work harder. Therefore, people with kidney problems should not eat high protein diets.
Kidney Function
Waste removal in kidneys occurs in tiny areas within the kidney called nephrons. In each nephron, tiny blood vessels intertwine with urine-collecting tubules, which act together as a filtration unit called a glomerulus. Extra fluid and wastes pass into the tubules and down into the bladder for excretion. The rate at which kidneys filter blood wastes is called the glomerular filtration rate, or GFR. Those with reduced kidney function have a lower GFR.
Types of Proteins
Three types of proteins appear in most human diets--meat protein, dairy protein and vegetable protein. Most studies use calculated total dietary proteins, but some break down the proteins into these specific categories. A study published in the "Annals of Internal Medicine" reveals that women with mild renal insufficiency who consumed high non-dairy animal protein had significantly decreased GFR over an 11-year period. Also, a high total protein diet was identified as a risk factor for a progressive loss of renal function in dialysis patients in a 2005 "Nutrition and Metabolism" article.
Hypertension
An estimated one in nine adults in the United States has chronic kidney disease, or CKD. It is classified into five progressive stages according to GFR testing. Hypertension is a major cause of CKD. In hypertension, the pressure of blood within the glomerulus is so high that it damages the filtration system and blood cleansing is impaired. Also, CKD from other conditions may block the filtration system and cause increased hypertension. Increased protein intake places additional stress on a system that is already strained.
Diabetes
Diabetes is the leading cause of kidney failure. About one third of people with diabetes get CKD. Uncontrolled diabetes causes the tiny blood vessels in the kidneys to become clogged and narrow due to the high blood sugar. Lack of blood damages the kidneys. Therefore, proper control of blood sugar reduces kidney damage and a protein-restricted diet decreases disease progression.
Other Risk Factors
Some families and certain racial groups have increased risk of CKD. African Americans, American Indians and Hispanic Americans have higher risks of CKD, which may be related to higher rates of diabetes and hypertension in such groups. Some other risks include a sedentary lifestyle, increased salt intake, smoking, proteinuria and old age. According to the U.S. Renal Data System, incidence of CKD has tripled in the last 20 years. High protein diets can exacerbate problems with CKD.
Diet
Dietary changes greatly assist those with kidney problems. Since excess blood proteins require increased filtration by the kidneys, low-protein diets may assist in decreasing kidney problems. Doctors, dietitians and nurses help formulate diets supporting maximum kidney functioning. A moderate diet includes 1g of protein per kilogram of body weight per day. A person must consume enough protein to remain healthy, so total elimination of protein is not recommended. Both animal and plant sources need to be included in the daily diet plan.
References
- Wake Forest University School of Medicine: Chronic Kidney Disease as a Public Threat
- National Kidney Foundation: Chronic Kidney Disease (CKD)
- Annals of Internal Medicine: The Impact of Protein Intake on Renal Function Decline in Women
- Nutrition & Metabolism: Dietary Protein Intake and Renal Function
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