Healthy or heathful?

[Lennihollander]

First of all, I have a huge question that needs answering. It’s not a hard vocabulary question but sometimes it bothers me a lot. It would be excellent if someone could tell me how to differentiate “healthy” and “healthful”. It’s very important since this word comes up quite often in my exercises about word forms.
For example: These fruits and drinks are healthful for our bodies. Why don’t we use “healthy”?
Secondly, could you give me the correct tense of the verb below?
If you read in bad light, your eyes (ruin). Is it “will be ruined”?
Thank you in advance!

[Our_Tort_System]

The distinction in meaning between healthy (“possessing good health”) and healthful (“conducive to good health”) was ascribed to the two terms only as late as the 1880s. This distinction, though tenaciously supported by some critics, is belied by citational evidencehealthy has been used to mean “healthful” since the 16th century. Use of healthy in this sense is to be found in the works of many distinguished writers, with this example from John Locke being typical: “Gardening . . . and working in wood, are fit and healthy recreations for a man of study or business.” Therefore, both healthy and healthful are correct in these contexts: a healthy climate, a healthful climate; a healthful diet, a healthy diet.

Courtecy of thefreedictionary.com/healthy

[Bookaholic_English]

I think healthful is an old fashioned word and used mainly to describe food. Now, healthy can be used to describe not only physical quality but also healthful food.