Here is a English usage worksheet on distinguishing between the adjectives healthy and healthful when deploying these words in prose. This is a full-page worksheet with a one-paragraph reading and ten modified cloze exercises. Like all the materials under the masthead “Common Errors in English Usage,” this one is adapted from Paul Brians’ excellent book of the same name; did you know he allows access to it for free at the Washington State University website?
In this reading, Professor Brians subtly argues that the difference between healthy and healthful has eroded to such a degree that the words are indistinguishable now. So, after working with them in these exercises, students can debate whether or not we need both of these words in our lexicons.
If you find typos in this document, I would appreciate a notification. And, as always, if you find this material useful in your practice, I would be grateful to hear what you think of it. I seek your peer review.