The average American knows even less about food than he or she does about the structure and functions of his/her body (this ignorance is part of a much broader scientific illiteracy).The proteins we make as the basic function of metabolism must be constructed from amino acids--we do not absorb steak. The amino acids (generic structure pictured) must be obtained from the break down of more complex proteins--we cannot manufacture them ourselves. Only amino acids--not Big Macs or protein shakes or nuts--can be absorbed from the gut. They must then be stored as proteins that cells can in turn use to manufacture their more complex protein products, e.g. hormones, neurotransmitters, other signal and transport proteins. The nitrogen that is the unique ingredient in proteins (as opposed to carbohydrates and lipids) has to be "fixed" by bacteria and then converted into plants proteins--we cannot utilize the nitrogen that is in the air around us (80% of air is nitrogen). The fact is we are part of two biomass-wide cycles--the Nitrogen and Carbon Cycles. Our wastes (and remnants!) in turn contribute carbon and nitrogen to this biomass. The foodies would have you believe these substances are unique and magical--they are not. We are simply a stage in the cycles--but thankfully so! Without them we would have died out millennia ago.
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