'metabolically' originates from Modern English, formed from the adjective 'metabolic' + the adverbial suffix '-ally'; 'metabolic' ultimately comes from Greek 'metabolē' meaning 'change'.

'metabolē' (Greek) passed into Late Latin/New Latin as 'metabolismus' and then into English as 'metabolism'; from this came the adjective 'metabolic' (English), and the adverb 'metabolically' developed from that adjective with the suffix '-ally'.

Initially the Greek root meant 'change' in a general sense; over time it became specialized to denote chemical changes in living organisms (metabolism), and 'metabolically' now means 'in terms of metabolism' or 'by metabolic processes'.