I often hear “healthy” — as in “healthy food” — when people mean “healthful”.

Problem:
The adjective “healthy” should not be used when one specifically is referring to something that brings about good health.

Explanation:
The primary definition of the adjective “healthy” is having or enjoying good health. The primary definition of the adjective “healthful” is conducive to good health. The secondary or tertiary definition of “healthy” has become conducive to good health, which is unfortunate and should be avoided.

I believe that the use of “healthy” in place of “healthful” supports my “Devolution toward Simpler” hypothesis. It’s simpler to say “healthy” than to say “healthful”, so many will call something “healthy” when what they really mean is “healthful”.

Still, it is worthwhile to use the appropriate word. Otherwise, you risk confusing the reader or listener.

For example, a healthy steer is different than a healthful steer. The first steer has good health; the second steer — presumably because of the eating of the beef produced from it — contributes to good health. Some vegetarians can reasonably argue that steers can be “healthy” but not “healthful”.

Solution:
Use “healthy” when you’re referring to possessing good health or characteristic of good health; use “healthful” when you’re referring to contributing to good health.