'protein-deficient' originates from the combination of 'protein' and 'deficient', where 'protein' refers to essential nutrients and 'deficient' means lacking.

'protein-deficient' combines the word 'protein' from the Greek 'proteios' meaning 'primary' and 'deficient' from Latin 'deficere' meaning 'to fail or lack'.

Initially, it meant 'lacking in essential nutrients', but over time it evolved into its current meaning of 'lacking in protein specifically'.