Health is not everything.

A, rice and steamed bread are rich in starch, which belongs to sugar and is the main supplier of human energy. Correct.

B, zinc and iron belong to trace elements, and calcium belongs to macro elements. Not correct.

C, fruit is rich in vitamins, eating fruit can't eat fat. Not correct.

D, sodium ion can regulate the balance of body fluids, but it can't help digestion. Not correct.

So choose: a.