The kidneys are two organs located near the sides of the abdomen that are an essential part of the urinary system. They help keep the blood clean and chemically balanced. According to the National Kidney and Urologic Diseases Information Clearinghouse, the kidneys process 200 qt. of blood every day and sift out about 2 qt. of water and waste products, such as the ones left behind by protein. The bladder stores urine until it is released through urination.
Proteins
Amino acids are the building blocks of proteins. They are unique among organic compounds because of their heavy reliance upon the atom nitrogen. A single protein may be hundreds of amino acids in length, so proteins are ultimately too big to pass through the filter of the kidneys, but the amino acids can be converted into a form that the body will excrete.
Ammonia
Amino acids can be broken down into nitrogenous waste products through a process known as deamination. This yields the production of ammonia, an extremely toxic substance that would raise the pH of the blood. Although it is small and mobile, ammonia is also fatal to humans if it accumulates in large doses in the body.
Urea
The liver contains a series of enzymes that can quickly convert two ammonia compounds, together with a single carbon dioxide, into a molecule known as urea, which is solid, colorless and odorless. This conversion is called the urea cycle. Though it is less poisonous than ammonia, your body cannot tolerate high concentrations of urea. This is why urea is removed efficiently by the kidneys.
Significance
On a high-protein diet, excess amino acids from ingested food that are not used for protein synthesis are oxidized for energy or stored as fat and glycogen. The remaining amino nitrogen is metabolized into urea. Extra enzymes are produced by the body for the sole purpose of carrying out this heightened state of urea production. The body will then excrete the urea, which can increase the frequency of urination.
Considerations
Experts and nutritionists are still debating whether too much protein can place stress upon the kidneys and potentially cause damage. Healthy kidneys should be able to cleanly and efficiently filter out urea from the blood. However, it is not recommended that you consume more than 3 g of protein per kg of body weight.
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