There’s a person for every diet plan. There are low-carbohydrate diets, low-fat diets, macrobiotic diets, vegetarian diets, raw food diets, etc., and for every diet, there is a different list of acceptable food. One thing that I’ve seen all diets have in common, however, is the espousal of eating healthy, eating a healthy diet, and living healthy.
Unfortunately, you can’t eat healthy. But don’t panic; it’s not all bad news. You can eat healthful food, and you can engage in healthful eating and even live a healthful lifestyle.
Healthy means free of disease. You can eat healthy vegetables (free of disease)—and, considering the alternative, who wouldn’t want to—but, generally, when you see or hear slogans calling for healthy eating, what they should really be saying is healthful eating.
Healthful means that something contributes to health, as in eat healthful food (food that is conducive to health), eat a healthful diet (a diet that is conducive to health), and live a healthful lifestyle (a lifestyle that is conducive to health).
A person can be healthy, and as I’ve already said, food can be healthy IF you’re describing food that is free of disease; otherwise, if you’re talking about something that encourages health or contributes to health, the word is healthful.
Some people (and some dictionaries) use both interchangeably, citing their uses as synonymous by some 16th Century writers; however, I’ve found inconsistencies both between dictionaries and within dictionaries.
Note: Being a writer doesn’t mean that you know everything about grammar. We like to assume that every writer knows and every editor knows everything about grammar and language, but we don’t. My own approach is to use the logic that extends from established grammar rules, and using healthful and healthy as synonyms doesn’t make sense, both based on my own logic and the inconsistencies that I’ve seen in dictionaries. The media as a whole likes to use them interchangeably, but you might, by now, know how I feel about the media’s negative influence on grammar.
Of course, you have to decide for yourself. My advice: Don’t mix healthful and healthy; it could be a recipe for disaster.
Sherry’s Grammar List and Paul’s book–Literally, the Best Language Book Ever