1.7.2 Too much protein
There is no way of storing large quantities of amino acids in the human body and so if more are present in the blood than are needed, the surplus ones have to be broken down and removed from the body. The liver carries out this crucially important function. The amino (nitrogen-containing) part of the amino acid is converted into a substance called urea, which contains the unwanted nitrogen. The urea is then carried round in the bloodstream to the kidneys where it is removed and then excreted from the body dissolved in water in the urine. All animals have to undertake a similar process to get rid of their excess amino acids, though the form of the nitrogen-containing waste product depends on how much water is available to dilute it. Fish produce ammonia, which is soluble and needs large amounts of water to remove it from the body, and can be toxic at high concentrations in the blood. Ammonia (in solution) is lost via their gills. Birds, which often do not have easy access to water, produce a semi-solid white sludge of uric acid. The remaining (carbon-containing) part of the amino acid can be broken down in humans and other animals, to provide energy or it can be stored by being converted to carbohydrate or fat, depending on the identity of the R group.