Did you know if you have chronic kidney disease (and aren’t on dialysis) too much protein can be harmful? In this post I will help you understand what protein is, how it is metabolized and why too much protein is not recommended for chronic kidney disease.
Protein is one of the three macronutrients (the others are carbohydrates and fat). It is essential for growth and maintenance of the human body. Proteins are made up of hundreds or thousands of chains of amino acids. Amino acids are not only needed for repair and maintenance of muscle – they are required for making hormones, neurotransmitters and are necessary to keep your entire body running. Food’s highest in protein are animal products such as meat, poultry, eggs, seafood and dairy. Plants-foods that are highest in protein include nuts, seeds, legumes and grains.
The recommended intake for protein for healthy adults is 0.8 g/kg body weight. For a 150 lb (68.2 kg) person, their protein needs would be 55 grams daily. Protein deficiency is uncommon in America. It is seen mostly in poor, undeveloped countries. The standard American diet provides excess protein. Excess protein isn’t necessarily a problem for healthy people (but it’s also not very beneficial). But if you understand how protein is metabolized, it may give you a better picture as to why it can be harmful for CKD.
Here is a quick run through of how protein is broken down in the body…
Digestion starts right when food enters the mouth. Saliva contains enzymes which begin to break down food along with the mechanical act of chewing.
Once the food enters your stomach, it is mixed with hydrochloric acid and an enzyme called pepsin which begins to break down the proteins into amino acid chains. The churning motion of the stomach is also important for the digestion process.
The food goes from the stomach into the small intestine. The pancreas releases two enzymes for protein breakdown (chymotrypsin and trypsin) into the intestine which continue to break down the amino acid chains.
Single amino acids are transported into the blood. Amino acids that aren’t fully broken down stay in the intestines and are excreted in the feces.
Amino acids are transported to the liver where they are used for protein synthesis and other purposes.
Ammonia is a waste product that comes from amino acid metabolism which is toxic in large amounts. The liver converts ammonia to a less toxic waste product called urea.
The urea then exits into the blood and travels to the kidneys where it is excreted in the urine.
What happens when the kidneys aren't working well?
As you may have guessed, since the waste product, urea, is normally excreted by the kidneys as urine, a kidney that is not working as well will have a hard time doing this. More urea than normal ends up staying in the blood circulation. If you have kidney disease, blood urea nitrogen (BUN) is monitored closely in your blood lab work. BUN greater than 24 is considered elevated. Protein intake is closely correlated with BUN in those with kidney disease. Thus, a higher protein intake means a higher BUN.
How much protein should I be eating if I have kidney disease?
Your protein intake is best determined by a registered dietitian as it depends on several factors. In general, those with pre-dialysis CKD are told to limit protein to 0.55 – 0.8 g/kg body weight. If reducing protein, it is important to make up calories with other macronutrients such as fat and carbohydrates.
Consuming more plant-based proteins is an effective way to reduce your overall protein intake. Plants contain less protein than animal products gram for gram. For example: 100 grams of chicken thigh has 27 g protein compared to 7 grams protein in 100 grams chickpeas.
If you are eating meat, limit the portion size 3 oz, which is equal to the size of a deck of cards, or less. Restaurant servings of meat can be double this amount- so order extra portion of vegetables if eating out and save half your meat entrée for the next day.
If you have a good appetite - protein drinks, protein powders of other high protein products (example: high protein yogurt, collagen) should typically be avoided. There may be instances where plant-protein drinks/powders can be utilized but it’s generally only needed for those who are malnourished or not eating enough.
So, if you have pre-dialysis CKD, be weary of eating too much protein, especially from animal products. Excess protein intake can lead to more waste products in your blood which stresses out your kidneys and can make you feel bad. Replacing some animal products with plant-protein sources is a great way to reduce your total protein intake. There are many other benefits to a plant-based diet I will discuss in my next blog post! Feel free to reach out to me if you are considering reducing your protein intake to protect your kidneys!