If the secretion of parietal cells in the gastric mucosa is blocked with the help of an inhibitor, protein digestion would be affected because

Parietal cells secrete HCl and intrinsic factor. HCl activates the proenzyme pepsinogen to pepsin. In the absence of HCl, pepsinogen would not be activated and hence protein digestion would be affected (pepsin digests proteins into proteoses and peptones).