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The use of healthy is preferred over helpful.
The American Heritage® Book of English Usage.
A Practical and Authoritative Guide to Contemporary English. 1996.
3. Word Choice: New Uses, Common Confusion, and Constraints
§ 156. healthy / healthful
Some people like to maintain a distinction between healthy and healthful. Healthy, they say, should be used to mean “possessing good health,” and only healthful should mean “conducive to good health.” People who hold this view are swimming against the tide of history, for healthy has been used to mean “healthful” since the 16th century. You can find the “healthful” use of healthy 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.