it 是形式主语:
to take care of what you eat.不定式是真正的主语.
留心/注意你所吃的东西.
can help your body (grow strong)
能帮助你的身体(变强壮)
can help your body——这是谓语和宾语.
括号内的(grow strong) 是省略了to 的不定式,做宾补.