The fact that the human body metabolizes ethanol to derive energy is a fundamental biochemical truism that requires no citation.
The claim states that the human body extracts energy from ethanol through metabolic pathways. This is a basic, universally established physiological fact: ethanol is metabolized in the liver via alcohol dehydrogenase and aldehyde dehydrogenase, yielding acetate which enters the citric acid cycle to produce ATP. Because this is a matter of common scientific knowledge, no citation is needed and Step 0 classifies it as such.