Unfortunately, there have already been protein spiking cases with very tragic consequences. A couple of years ago in China, a material of very high nitrogen content was added to milk in order to boost its apparent protein content. However, the added material was highly toxic and many children lost their lives for consuming it.
It is a less cruel, but equally unfair method to add cheap, but not harmful nitrogen sources to the protein. These can be amino acids with a higher-than-average nitrogen content (like glycine), cheap collagen, but also arginine.