A nitrogenous waste product of protein metabolism formed in the liver and excreted through the kidneys in urine. When the kidney function is compromised through disease, dehydration or circulatory disturbance, urea accumulates in the blood. The level of Blood Urea Nitrogen BUN is used as an indicator of kidney function. In chronic kidney disease urea can exert toxic effects on a number of different organ systems including depressing bone marrow leading to anaemia, altering fat metabolism, and disturbing the gut microbiota leading to increased absorbtion of bacterial toxins from the gut. Feeding high levels of protein drives more urea production which must be eliminated to prevent toxicity, thereby placing additional load on liver and kidney function. Generating more urea is the downside to feeding high protein diets.