Having noticed my pants fitting a bit too snugly, and having foolishly counted the number of times I ate at the combination Taco Bell/KFC in one week (around 4), I have recently been considering trying to get into shape. (My recent use of our new fryer to create fried Oreos and fried cinnamon buns has added to these concerns as well.) Part of that involves renouncing the siren song of the Beefy 5-layer Burrito and steering myself toward salads and junk like that, what one might call “healthy” food.
Or mightn’t one? Some people insist that one mustn’t. Healthy, in these people’s world, means only possessing good health. Healthful is the only correct form for food and other objects that induce good health in others, they say.
And, as you might have supposed, they’re bonkers. Obviously, healthy and healthful are both valid in their respective meanings given above — good job on that front, at least — but there’s nothing wrong with using healthy to mean “promoting or inducing good health”. MWDEU says that the whole notion that something’s wrong with that usage can be traced back to 1881, when a fellow named Alfred Ayers declared it so in a book called The Verbalist. (Google Books has the 1909 edition online.) The trouble with Ayres’s declaration is that it spit in the face of at least 330 years of usage; the OED’s first citation for healthy, in 1552, defines the two words identically, and both meanings for healthy are attested all the way up to Ayres’s book’s publication. (Here’re a few examples, from 1744, 1793, and 1828.)
So unless you think Ayres knows something about English that no else does, you can safely ignore his broad-cloth assertion. It’s fine to use healthy to mean “promoting good health”, and the prescribed restriction is poppycock.
But there is a small seed of truth to Ayres’s belief: healthful has all but lost its ability to mean “possessing good health”. That’s weird, because healthful, following the commonest meaning of the -ful suffix, would be expected to mean “full of health”. But that meaning has been largely lost to healthy. “Healthy people” has 2,030,000 Google hits, “healthful people” only 4,960 — a 400:1 ratio. “Healthy food” has 3,590,000 Google hits, “healthful food” has 99,300 — a 36:1 ratio. In both cases, healthy is more common, but healthful is less overwhelmed in its “promoting health” meaning than in its “possessing health” meaning. I find this a nice counter-example to any claim that English suffixation is obligatorily logical.
And if you’ll excuse my ending on an aside, this is one of the weirdest pieces of advice I’ve ever heard: it’s wrong to use healthy as a literal adjective meaning “promoting health”, but it’s fine to use it to mean “metaphorically promoting health”. So (1a) would be wrong and (1b) would be fine.
(1a) I’m eating some healthy foods. [“BAD”]
(1b) I have a healthy fear of viruses. [“GOOD”]
That, my friends, is daft.
Summary: No matter what prescriptivists say, healthy can mean “possessing health”, as in healthy people, or “promoting health”, as in healthy food. Both meanings have been attested for 450 years, and the claim against the latter was an unjustified assertion from 1881 by a prescriptivist otherwise lost to the sands of history. Healthful can mean “promoting health” or “possessing health” as well, although the latter usage is nowadays rare.