'low-magnesium' originates from Modern English, formed by combining the adjective 'low' (ultimately from Old English roots meaning 'not high' or 'of small amount') and the element name 'magnesium' (from New Latin 'magnesium', ultimately from Greek 'Magnesia', a place name where certain minerals were found).

'magnesium' entered scientific vocabulary in the late 18th/early 19th century from New Latin 'magnesium', itself derived from the Greek place-name 'Magnesia'; 'low' has been used in English since Old English to mean 'not high' or 'small in amount'. The compound 'low-magnesium' is a modern English descriptive formation combining these two words.

Initially, 'magnesium' referred to minerals associated with Magnesia, and later became the name of the chemical element; 'low' has long meant 'not high' or 'small in amount'. Together the compound simply denotes 'having a low amount of magnesium' without major semantic shift.