Close. Incomplete proteins are surplus amino acids because synthesis of proteins for use by the body takes complete sets of amino acids. Energy and molecules aren’t the same thing. It takes energy to break chemical bonds. The net energy taken to break protein down is more than the energy provided by the resultant glucose, there is junk left over that has to be dealt with by the kidneys. Excessively high protein diets are taxing on your kidneys over long periods of time. Protein molecule on the left, glucose on the right. 
Discussion
Ah, good point! Without enough essential amino acids, you’ll have a surplus of non-essential amino acids and the liver can only store so much, so your kidneys take the hit and have to get rid of it.
Just keep in mind that incomplete proteins =/= only non-essential amino acids. Incomplete proteins also contain essential proteins, just not all 9 of them. Though, I would need to look up actual breakdowns to get a feeling for the essential / non-essential ratios.
I did look up some more information on the metabolic cost of processing proteins and it seems like there are more energy costs involved than I was taught in uni. Next to breaking down proteins into amino acids, there’s also the conversion of amino acids into other amino acids, protein synthesis, folding, transportation, posttranslational modifications and other processes.
yes, excess protein leads to two things: ammonia production and conversion to glucose, depending on the ratios of aromatic ring containing amino acids (phenylalanine, tyrosine, tryptophan) and this pH raising can cause problems with blood solubility of all kinds of things
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