Cost and Effect

Sometimes the word "cost" only bring a monetary idea to to mind. However, the word can hold a much broader meaning. One of the definitions of cost can be put this way: "...cost is the loss or penalty incurred, especially in gaining something..." Thus, in looking at the cost of protein, as we have been for some weeks now, what is it that we are losing in order to gain that nutrition?
A rising concern in today's society is the concept of "sustainability." This term relates to resources that are utilized without permanently damaging or depleting them. How can we look at this as pertains to protein? To be fair, most protein sources are basically sustainable in and of themselves. Plant based protein sources are able to regenerate through their seeds. Animals are also able to reproduce - in a comfortable or natural environment they may even multiply and flourish. The issues of utilizing these different sources for proteins don't arise until we do just that, utilize them. It is in the way proteins are harvested and in the amounts taken from each source that sustainability becomes a concern.
The protein diet in the U.S. is primarily an animal-based protein diet. The U.S. food production system uses around 50% of our total land area. We use about 80% of our fresh water for food production. 17% of the fossil energy we use in America is for the production of food  - much of which is animal-based proteins (dairy and meat). On top of that, animals are fed protein-rich grains and plants in order to become a protein source themselves.
One of the impacts of cattle and other animals being raised in the U.S. is soil erosion. According to research, 60% of U.S. pastureland is being overgrazed and is subject to accelerated soil erosion. We are losing soil in pastureland at a rate of .10 inch per year. Which means, in 10 years we will have eroded 1 inch of soil. That doesn't sound like much, until one considers that is takes 500 years for 1 inch of soil to be replaced! Our croplands are also eroding at an unhealthy rate, but only at 1/6 of the rate that pastureland is eroding at.
Unfortunately, both protein diets require significant amounts of non-renewable fossil energy to produce. In the long run, neither will remain sustainable forever - until an alternative energy for production can be found. Until that time comes, plant-based protein sources use a much lower quantity of fossil energy to produce. For now, it is the technically more "sustainable" option, environmentally speaking, when choosing which type of protein to consume. 

For Further Reading:
proteincostawareness.weebly.com

Sources:
ccbcmd.edu
nutrition.org
huffingtonpost.com
merriam-webster.com