One of the great moves Nietzsche makes in "Ecce Homo" is to introduce the figure, the function, of metabolism. His view of metabolism is not limited to the digestion of food. Books, events, art, people: these are all things that we take up, that we consume, and that we metabolically distribute: we use this part, not that, at this or that speed, in this or that manner.
Our very selection of things — friends, recreation, location, literature — stems from our appetite, from our taste. ("Stems" is not quite right because it suggests there is a self before taste, which is not quite right. We are our taste; or our taste makes us; or we are our tasting.) Each of us desires — and needs — different things. We are drawn to different things. The strong, according to Nietzsche, are those who instinctively desire those things that fortify health, that enliven, that strengthen. The weak — the decadent — are those who choose things that make them sick and tired, that make them weak (a tautology? No: the weak are, well, weak — they perpetuate their weakness).
We know these people (usually in our families or jobs). We know this weakness in ourselves — we find ourselves doing things that are shitty. I don't mean things like drinking and fucking and getting high; I don't mean shitty in a moral sense. I mean shitty in the sense of how it affects our fundamental health. (A certain amount of booze, and certain booze, fortifies me for sure. There is a line between alcoholism and a certain metabolic need but this line can, at times, become confused by some.)
This, to me, is what's so troubling about watching someone absentmindedly eat through a bag of Doritos or a pack of cigarettes or a bottle of Jim Beam. Of course, there is the rare person for whom such things are in fact enlivening. But these are rare people. Witnessing such flagrant displays of bad instinct is painful (especially in oneself). It's watching someone — sometimes oneself — die badly.
We eat the world and, in so doing, make ourselves: a productive consumption. And metabolism sits at the juncture of self and world (along with taste — taste is the tongue and fingers of metabolism). We take in the world and make sense of it within the elaborate engine of our being, an engine that includes intestines and moods, erections and dreams, burps and ideas. Metabolism is the function of taking in and spitting out the world, of distributing the world in a particular manner, at a particular speed, making sense and making self.
All things have some kind of metabolic function. A rock, for instance, takes in sun and dirt and earth and bugs and rain in its own way. Different rocks do it in different ways and certainly in ways that are different than what you or I do — although certain people have rock-like metabolisms (not a bad thing, mind you).
We choose books, we choose recreation, we choose work, we choose friends and lovers just as we choose food. It's all a matter of appetite, taste, and metabolic distribution.
From time to time I like to pause and look at my life, at how I make my way through the day, through the week, through the year. I consider how often I find myself in distasteful situations — fighting with friends, with co-workers, with family members, cursing at cars (I never fight with friends — perhaps because I don't have any friends. Which may be why I don't have any friends. But I'm always surprised to learn that people do, in fact, fight with friends. This seems odd to me, But many things are odd to me). These are signs of a sickly metabolism at work and is a call for change.
According to Nietzsche, the strong are those who discipline themselves, who train their instincts (another great move Nietzsche makes: we can train our instincts!). The strong work themselves over like a piece of art, like a sculpture, chipping away the poor instincts, strengthening the strong ones.
To consume this life well — and hence to make oneself well — is an on-going negotiation. Of course, metabolism is itself the act of negotiating — which makes negotiating one's metabolism tricky. But such is this Mobius life: a hammer making itself with a hammer.