1. healthy 有两个意思，一是指“人本身健康的”，二是指“有益于健康的”。如：
Good food keeps you healthy. 好的饮食使你健康。
Cycling is certainly healthier than driving. 骑车肯定比开车有利于健康。
有时用于比喻义。如：
That book is not healthy reading for children. 那本书供小孩读不健康。
　　
2. healthful通常只表示“有益于健康的”。如：
Doing morning exercises is very healthful. 做早操对健康很有益。
Why don't you eat such healthy [healthful] foods? 你为什么不吃那些有益于健康的食物?
此词在现代英语中用得不多(已属过时用法)，一般用healthy代替。