Dietary Protein and Chronic Kidney
Protein: An overview
Protein is made from chains of amino acids. Amino acids are often called “the building blocks of life.” There are 20 amino acids. They combine in different ways to form a variety of proteins the body uses to create cells, hormones and enzymes. Eleven of these 20 amino acids are manufactured in the body by the liver. The other nine, called “essential” amino acids, can only be obtained through diet.
Amino acids are abundant in protein-based foods. A food is said to be a “complete” protein when it contains all of the nine essential amino acids we need. Most animal based protein foods such as eggs, meat, fish, poultry, cheese and milk are complete protein foods. Some soy products also contain the nine essential amino acids. Complete protein foods are sometimes referred to as high biological value proteins. Plant proteins such as grains, legumes, seeds and nuts are considered incomplete proteins, because they have low amounts or are missing one or more essential amino acids. Incomplete protein foods are sometimes referred to as low biological value proteins.
When we eat foods that have protein, the body breaks down the long chains of amino acids into single amino acids. The body’s cells use these amino acids to manufacture new proteins. Proteins are used to:
- repair tissue
- make hormones
- antibodies and enzymes
- help balance acid-base, fluid and electrolytes
- provide some of the body’s energy
Seventy-five percent of the human body is made of protein. Without protein, our bodies would be unable to heal from injury, stop bleeding or fight infection. That’s why eating protein (especially complete proteins) is so important to staying healthy. The average person needs between 40 to 65 grams of protein each day. The exact amount is based on body size and health status.
Protein and the chronic kidney disease patient
Protein can be tricky for chronic kidney disease (CKD) patients. Although protein is a necessary nutrient, CKD patients are often faced with the dilemma of having to limit protein intake.
When protein is ingested and used by the body, protein waste products are created. Healthy kidneys have millions of nephrons that can filter this waste. It is then removed from the body in the urine. Healthy kidneys can easily remove protein waste, even when very large amounts of protein are eaten.
Unhealthy kidneys lose the ability to remove protein waste. Protein waste starts to build up in the blood. As kidney function continues to decline, more waste accumulates. Blood tests that measure protein waste include blood urea nitrogen (BUN) and creatinine. These tests help your doctor assess how much the kidneys are working. A lower protein diet may be prescribed to help reduce waste accumulation. Some studies show that reducing protein intake may help slow the progression of kidney disease in some people. Dietary protein intake for CKD patients is based on the stage of kidney disease, nutrition status and body size. Low protein diets can cause protein malnutrition, and therefore should not be followed without medical supervision. Counseling sessions with a registered dietitian who provides medical nutrition therapy is recommended for planning and monitoring effects of a low protein diet.
CKD patients who are undergoing dialysis are often told to increase their protein intake. So why can some CKD patients eat large amounts of protein while others cannot? The most important factor in determining protein intake is the stage of CKD you are experiencing.
Protein and the stages of chronic kidney disease (CKD)
The five stages of CKD are defined by the glomerular filtration rate (GFR), a measure of how much blood the kidneys are able to filter. This rate tells you and your doctor how well your kidneys are functioning.
In Stage 1 of CKD, glomerular filtration rate is 90 or above, which is normal. However, abnormal levels of protein are detected in the urine. In Stage 2 of CKD, GFR is 60-89, a mild decrease from normal. In Stage 3, there is a moderate decrease in GFR to 30-59. In Stage 4, GFR is severely decreased to 15-29.
Stage 5 of CKD occurs when GFR drops below 15, and the kidneys have very little function left, this is end stage renal disease.
Although Stage 4 indicates a severe decrease in kidney function, you are still able to live without dialysis. Kidneys are damaged, but are able to filter some waste and excess fluid from the blood. Since there is no cure for kidney disease, the primary focus is keeping you well nourished and reducing protein waste build up in the blood. Excess protein waste can cause nausea, loss of appetite, vomiting, weakness, taste changes and itching.
The most important treatments to prolong renal function are blood pressure control and attention to protein in the diet. If you have diabetes, blood sugar control is also important. By regulating the amount of protein you eat, your kidneys process less protein waste, which reduces waste build up in the blood. It also reduces the workload on the kidneys, and may slow down the progression of kidney failure. Your diet will include a prescribed amount of high quality protein foods. This is to be sure you are getting enough essential amino acids each day.
If you are in stages 1, 2, or 3 of CKD, your protein intake may be limited to 12-15% of your calorie intake each day. This is the same level recommended by the Dietary Reference Intakes (DRIs) for a healthy diet for normal adults. It may seem like a restriction because the average American eats a high protein diet. If you are in stage 4 of CKD, you may be advised to reduce protein to 10% of calorie intake each day. Your dietitian will assess your nutritional status and calorie intake to help determine if a lower protein diet is beneficial.
Protein and end stage renal disease
Patients who are in stage 5, the last stage of kidney disease, need dialysis to live. This stage is also known as end stage renal disease or ESRD. The kidneys are working at less than 10% capacity. This means your kidneys cannot process the accumulated waste and fluid your body produces on a day-to-day basis. Dialysis is required to take over for the failed kidneys. Dialysis is needed indefinitely or until a kidney transplant is possible.
Dialysis treatments remove protein waste from the blood. A low protein diet is no longer needed to control protein waste buildup since this is accomplished by dialysis. Unfortunately, some amino acids are removed during dialysis. A higher protein intake is needed to replace dialysis protein lost and to help keep you well nourished and healthy.
Your dietitian will coach you on an eating plan designed to provide enough protein to meet your individual requirements.
This added protein will ensure you won’t lose muscle mass and that your body will have the resources to help fight infection. This is especially important for malnourished and elderly patients.
Diabetes, chronic kidney disease and protein
If you have chronic kidney disease as a result of diabetes, your dietitian and doctor will focus on helping you manage your diabetes. Good glucose and blood pressure control can help slow down the progression of kidney disease in people with diabetes. Your dietitian will determine the level of protein restriction you need and develop an eating plan that will help manage your diabetes and kidney disease.
Are some proteins better than others?
High protein foods like meat, milk and eggs can be high in fat and cholesterol. If you have high cholesterol or cardiovascular disease, your doctor and dietitian may recommend eating protein-rich foods that are more heart friendly. Good choices include fish, chicken breast, lean red meats, low cholesterol egg product, and low fat soy products as well as low fat dairy products.
Phosphorus is a mineral that builds up in the blood as kidney failure progresses. You may be advised to reduce high protein foods that are high in phosphorus, if your level goes above normal. Milk, yogurt, cheese, dried beans and peas, nuts and seeds, peanut butter and some soy products are high in both protein and phosphorus.
How can I manage my protein intake?
There are several things you can do to make sure you are getting the right amount of protein for your condition. First, speak with your renal dietitian. Your dietitian will give you specific guidelines regarding your protein intake and will tell you how many grams of protein you should have each day. This number will depend on the stage of kidney disease you are in, your lab results, your body size and other health conditions you may have. Your renal dietitian can also answer questions you have about protein.
If you are prescribed a low protein diet, your portions of protein containing foods will be smaller than usual. For the average size person, meat, poultry or fish is limited to about 4 to 6 ounces per day. Other protein containing foods are also limited to small portions. Your dietitian will give you a meal plan and information about how many grams of protein are in various food items so that you can count accurately. This will help make counting your protein easier and help you make the best choices.
If I can’t have protein, what can I have?
Although your diet may be limited in high protein foods, you will still eat a variety of foods. You will eat small portions of high protein foods such as eggs, milk, meat, poultry and fish. You will eat fruits, vegetables and grains. Eating adequate calories is important to prevent muscle breakdown and weight loss. You may be advised to eat more healthy fats, such as olive oil, to help you get enough calories. Sometimes a calorie supplement is prescribed to help increase calorie intake.
Depending on your condition, you may also need to limit other components in your diet, like sodium, potassium or phosphorus. This is determined by your blood pressure and your laboratory values.
Your renal dietitian will coach you on alternatives to foods you need to reduce or avoid. They will provide information such as grocery lists, menus and guidelines for eating out. Although diet change is challenging, the benefit is that you may slow progression of your kidney failure. In addition, you will stay well nourished and feel much better.