In the realm of physiology, being “metabolically flexible” means that your body can use whatever fuel is available to meet its energy demands. It can readily switch between burning carbohydrates or burning fat (whether that’s fat you ingest or fat already stored in your cells).
While a metabolically inflexible individual gets cranky and lethargic if they go several hours without carbs, the metabolically flexible individual can run for miles powered only by eggs — or nothing at all — and can fast from food for a day or more without becoming irritable or listless.
Metabolic flexibility is not only a good goal for physical health, but an excellent paradigm to apply to one’s emotional and psychological condition.
The metabolically flexible psyche adeptly operates off routine, but is also animated by chaos. It enjoys solitude without loneliness, and can find a mountain as companionable as a person. It experiences sadness not as a function-debilitating burden, but as an introspection-facilitating stimulus. It finds criticism as motivating as compliments.
He who possesses this kind of hybrid, multi-fuel-combustion psyche knows that, with a few exceptions (and these are in degree rather than kind), every emotion and state, effectively metabolized, can serve as a healthy spur towards thought and action.
You achieve metabolic flexibility of body by intentionally going without carbohydrates or food. You achieve metabolic flexibility of mind in a similar way: exercising without music to practice being alone with your thoughts, spending the occasional weekend roughing it in the woods — choosing bits of voluntary hardship.
In this way, whether you are fasted or fed, whether life serves up a steady supply of the sweet and easily digestible, or presents a dish of plainer, sterner fare, you’ll have the adaptability to thrive — the ability to chew up the equivalent of iron nails and find it a delicious, satisfying meal.