Our society programs us to be consumers. If we take up a new hobby or interest often our first reaction is to search for what things we need to buy to partake in that activity. The problem for business is that certain activities such as exercising with weights or running do not need that many material things, so the solution is to create things that seem they may help. Specialist foods seem to be a very successful niche.
I came across this article the other day, which pretty much confirms what I had suspected about protein supplements. Your normal everyday diet contains ample protein for your needs. If your diet did not contain protein, which is highly unlikely, your body can make proteins from amino acids which it can synthesise from the citric acid cycle using glucose and body fats which you probably wanted to reduce anyway.
Save your money and buy my books instead.