Dietary protein for the person with chronic kidney disease
(pre-dialysis)

As a person's kidney function diminishes, the dietary restrictions needed to compensate are increased. One of the more difficult dietary changes to master is protein requirements. Before we can understand why protein requirements change, we need to understand how the body treats the proteins we eat.

What are proteins?

The story of proteins must begin with amino acids, the structural units of proteins. Protein is formed by linking amino acids together - not unlike pearls on a necklace. There are about 20 amino acid building blocks (depending how they are defined); out of these twenty, ten are considered essential amino acids and the other ten non-essential. An essential amino acid is one that the body cannot make and must be supplied by the diet. The non-essential amino acids are necessary for health and life, but the body can manufacture them from the other essential amino acids. Foods containing the essential amino acids are called "high biologic value" or HBV protein foods.

Dietary Protein

The protein we eat is digested and broken down into its amino acids, which our body then uses to build its own proteins. These proteins perform thousands of functions, including the formation of connective and muscle tissue, producing enzymes to promote chemical reactions, or building larger substances needed for life, like the hormone insulin or the hemoglobin in red blood cells.

Protein digestion begins in the stomach and intestines. The amino acids then go into the blood stream and are transported to other parts of the body where they are absorbed and used as needed. The body needs different amounts of the various amino acids and it is possible to eat more protein than the body needs. When this happens, the excess amino acids are removed as waste (urea is an example of a protein "waste product"). One of the most important methods of removal is through the kidneys and out in the urine.

Proteins and the Kidney

The more amino acids that need removing, the harder the kidneys have to work. And for people with kidney disease, this can mean an acceleration of their kidney disease. So if a person stops eating protein, then they are saving their kidneys, right? No, because if we didn't eat protein, then malnutrition would develop and more illness would occur. So the solution is to eat enough protein to maintain health, but to minimize the excess amino acids and spare the kidneys. The way to do this is to eat foods with proteins that cause the least waste, that is, foods that have the right amounts (ratios) of different amino acids that the body will use most efficiently. Since we are animals, foods that come from animals (dairy foods, eggs, meat, poultry, fish) have the best combination of amino acids and produce the least waste- the "high biologic value" or HBV foods. [For a while, there was a marketing campaign calling eggs the "perfect food". That was because the ratio of amino acids in eggs is very close to the ratio that the human body needs and have an HBV of nearly 1.0, which is the ideal.]

It is important to understand that grains, legumes (beans), fruits and vegetables all have varying amounts of protein made of the same amino acids in animal foods. They are not "bad foods"- its just that the amino acids they have are not in the same amounts that the human body can use most efficiently- that is, they produce more waste. This is not universally true, there are good quality vegetable sources such as soy beans that can also be used. People with kidney disease need to pay attention to both the amount and type of protein they eat.

 

How much protein is enough?

A healthy, active person needs about 0.36 grams of protein per pound of body weight. The average American consumes over 100 grams of protein a day, or about 0.67 grams of protein per pound or almost twice what they need. So, a place to start for the person with kidney disease is to stop eating their usual amounts of protein and restrict their intake to only what their body needs.

Let's do a little arithmetic:
The average American man of 150 pounds is eating about 100 grams of protein per day, but only needs 54 grams. The current recommendation for a pre-dialysis diets for this person is 37-41 grams of protein per day (these numbers can vary depending on the stage of kidney disease). This means if you cut back to the recommended intake for a healthy individual, you have already nearly met the restrictions required for the pre-dialysis kidney diet! In order to reduce protein waste, it is recommended that 60% or more of the protein should be from HBV sources.

Some more arithmetic:
Different foods have different amounts of protein. Animal or HBV foods (meat, fish, poultry) have 7.0 grams of protein per ounce (milk has 4 grams per half-cup). Fruits (trace), vegetables (1.0 grams), and grains such as pasta, breads, cereals (2.0 grams) have lower amounts of protein per serving. Fats such as butter and oils have no protein- but they do have calories! (See Kidney Diet Project (KDP) pages for serving sizes.)

We now have enough information to work out a diet for our average 150-pound man:
Target protein intake: 40 grams of protein per day with (for example)
70% coming from HBV foods: 40 X 70% = 28 grams or 4 ounces (28/7)
40 X 30% = 12 grams of protein from other foods.
These 12 grams can be supplied with different combinations, but variety in the diet is important, both for maintaining health and also to keep the diet interesting. An example could be 3 servings of vegetables (3 grams), 5 grain servings (10 grams), and 3 fruit servings (0 gram) for a total of 41 grams.

Sample daily intakes for early kidney insufficiency.
Body weight (pounds):	Protein (grams)	Calories
100	25-27	1600
125	31-34	2000
150	38-41	2400
175	44-47	2800
200	50-54	3200

It is difficult to get exact intake, the goal is to consistently be close to your goals. In this case, we came up with a total of 41 grams- tomorrow it may be 39. It is also important to make sure you are eating enough calories. If your calorie intake is too low, your body will use the protein you eat for energy, rather than maintenance. Remember these numbers will change depending on your weight, gender, and the stage of your kidney disease. Your dietitian can determine the best amounts for you. It's important to be sure the protein restricted diet is still providing enough protein to maintain muscles and general health. This is determined by reviewing your blood tests.

This type of diet is probably different from what you are used to and will take practice and experimenting to master. But modifying your diet is one area where you can take charge of your medical treatment. Your dietitian can help with recipes and menus to keep protein intake at a healthy level, yet keep your diet interesting.

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