This isn't supposed to be irreverent, so please don't take it as so, but the human body is one of God's greatest creations and yesterday in a class we learned the price the body pays to recycle. This entry may take a little biochemistry background to understand, but I'll do my best to make it so all can play along. If you get lost in the biochemistry, the last paragraph is where I finally get around to making my point.
We need energy all the time and glucose is generally known to provide a considerable amount of that energy (we're not talking about fat today, but I know that it plays a huge role as well). To give us energy (ATP), sugar (glucose) goes through glycolysis which changes it from the 6 carbon glucose to a 3 carbon pyruvate molecule. We get a couple ATPs for every glucose molecule that goes through glycolysis. The body can either change pyruvate to Acytl CoA to enter the Krebs cycle where it will yield LOTS of ATP, or it can be converted to Lactic acid (you know, the stuff that makes your muscles burn during high intensity exercises). Previously it was thought the only time that pyruvate went to lactic acid was during high intensity exercise, but they are now finding that at rest, a considerable amount of pyruvate changes to lactic acid (in my field we call that exciting research, do you feel yourself getting excited?)
Lactic acid breaks down almost immediately to lactate and a hydrogen ion. We're going to forget about the hydrogen ion for the rest of this post. What does lactate do? It has always been considered a bad thing, why is it being produced by muscles at all times? It turns out that lactate can enter cells and ultimately the mitochondria where it is transferred to pyruvate, Acytl CoA and goes through the Krebs cycle. So we now have this lactate stuff that can go anywhere in the body and be used as fuel. At rest, 20-30% of all energy comes from lactate, and it is preferred over glucose as a fuel source. (This is another point where you are supposed to be excited).
During times of rest when lactate is especially high (like right after exercise), lactate is the preferred substrate for replenishing glycogen stores. This is the part where I have proof that God recycles. Instead of using glucose that is floating around in the blood which would take no alterations to be put into a glycogen molecule, the body chooses lactate to make glycogen. That will cost the body 6-10 ATP! (remember we only got a few ATP from converting glucose to lactate). So the body uses the stuff just sitting around to make new glycogen and prepare for the next exercise bout. Not only does our body recycle the lactate, but it goes through a great expense to undertake the recycling process. Why were we designed like that? I don't know, but it certainly seems to me that the One who created us didn't want to be wasteful. What are we doing to the earth that He created for us?