Best thing in life that’s free: (1) protein molecules in cytoplasm battered by kinetic energy of water molecules, (2) each protein molecule receives 107 KBT/ms. (3) this moves protein stochastically between its various conformations (mostly inactive). However, sooner or later they become active (actually very soon). We need to stabilize the one active form that needs just a tiny bit more energy: ~20 KBT over 1ms.

So where does this come from.  Less would be insufficient; more would be wasteful. This energy comes from

ATP (universal energy packet that drives most cellular reactions) delivers 20 KBT (optimal). So, to drive intracellular chemistry, the enzyme ATP synthase makes 45kg/day! It is just cranking it out! This is not a simple enzyme, but rather a nano-turbine that grabs ADP + PO4-3, forcing them together to produce 1 ATP with every 1/3 turn. Each turbine in the mitochondrial membrane rotates at 9,000 rpm!

So, the question is: How efficient? i.e., how much energy is used to drive the turbine is converted into ATP? The answer is: 90%. So, what this means is that we have an optimally sized energy packet is optimally produced.

How efficiently does the whole animal capture nutrients from food? The Gut optimizes nutrient absorption across scales: nanometers to meters.

Here is a picture of the Intestinal microvilli (90nm diam).

The surface area of the Microvillar is increased and they are packed optimally for protein transporters.  They are as small as can be and are packed tightly together They are completely covered on the surface with protean transporters that pump in glucose and all of the nutrients from the gut that go into the bloodstream.