PART I — The Hog
Energy, so it seems, is nothing more than moving electrons — chemical energy, that is. This includes caloric energy. The energy we get from foods is contained in the bonds between the individual atoms within each molecule. Mostly this energy comes from the macronutrients — the carbohydrates, fats, and protein — but for all too many the predominance of their dietary energy comes from alcohol. More about that another time.
Animals mostly obtain energy from carbohydrates and fats. More specifically, animals with the capacity for (and inclination to) locomotion prefer fats, at least for long-term energy storage. Gram for gram, fat metabolism provides more than double the energy as that of carbohydrates. Furthermore, and unlike carbohydrates, fats can be stored dehydrated (without water). This provides a distinct weight advantage compared to carbohydrate storage.
In combination, these two characteristics (energy-richness, and lighter storage) mean fats are six times more energy dense than carbohydrates — hence the mandatory attention to dietary fat intake for those looking to lose weight, and quite apart from the cardiovascular benefits.
As we slowly burn (combust) our food fuels, we are also aiming to minimise the ubiquitous oxidation of the functional and structural elements of our organism. Our bodies are in a constant battle against oxidation. Yes, we rust. And to that end we hear a lot today of antioxidants. That, too, is another topic for another day.
Efficient metabolism of fuels in humans is significantly favoured by an aerobic (oxygen-rich) environment. That man cannot live without oxygen is as plain as the nose on your face. But why do we need this oxygen? What is it about oxygen that is so absolute to our existence?
The external manifestations of low oxygen saturation in the blood is the foreboding blue discolouration of the skin and membranes, known as cyanosis. Cyanosis, per se, is only the external manifestation of low oxygen in blood. But this low blood oxygen level is a lagging outward display of the cellular switch to anaerobic metabolism.
And here’s the rub: anaerobic metabolism is — unfortunately — extremely inefficient at producing energy compared to metabolism in the presence of abundant oxygen. It is oxygen — via oxidative phosphorylation — that allows for efficient translation of chemical energy into a provision of immediately available cellular energy (ATP).
But what exactly about oxygen in the air that we breathe is so life-giving and preserving?
As it’s name suggests, oxygen is the great oxidiser (again, think rusting). In chemical terms, this means that oxygen has a very high affinity for electrons. That is, oxygen is a potent electron acceptor. Oxygen is an ‘electron hog’.
In all chemical reactions, it is the electrons that make the moves. Whizzing around the atomic nuclei, electrons often jump from one energy level to another as they come near other electrons from the same or nearby atoms. When an electron has cause to “zap” down an energy level (or orbital), it releases energy in a small, uniform, packet known as a quantum. It is this quantum that drives oxidative phosphorylation — the most efficient means, by far, of cellular energy formation.
Without oxygen, electrons have ultimately nowhere to go and oxidative phosphorylation stops. Electron carriers in the mitochondria back-up, bringing the Krebs cycle to a halt also. Man cannot tolerate this low-oxygen environment for more than 3-6 minutes, before our highly metabolic neurons are critically depleted of energy. Energy-deplete neurons lose the ability to control their electrochemical gradients and to fire and propagate impulses. Ultimately, organelle and cell membrane integrity is lost and the neuron quickly succumbs.
Oxygen, then, is about being able to create enough ATP (from those high-energy electrons) for the high-metabolic needs of, in particular, brain cells. High-energy electrons, stored in the chemical energy of food, are used to make vital ATP-energy for cell survival. Ultimately, it is the pull of oxygen that carries the high-energy electron on its path along the ox-phos respiration chain, to which they ultimately combine to form water as a by-product.
Oxygen is the final electron acceptor — the “magnet” that pulls the high-energy electrons down the electron chain, releasing quanta of energy as they go (which is utilised to synthesise ATP from ADP). Oxygen is an electron hog. And the electron hog drives ATP production. Less oxygen: much less efficient ATP production. Little or no oxygen: not enough ATP produced to keep the cellular machinery alive.