These terms refer to the residue of the metabolism of foods. The mineral salts of sodium, potassium, magnesium, and calcium are base-forming, while phosphorus, sulphur and chlorine are acid-forming. Which of these predominates in foods determines whether the residue is acidic or basic (alkaline); meat, cheese, eggs and cereals leave an acidic residue, while milk, vegetables, and some fruits leave a basic residue.