Seen any walnuts in your medicine cabinet lately? According to the Food and Drug Administration, that is precisely where you should find them. Because Diamond Foods made truthful claims about the health benefits of consuming walnuts that the FDA didn’t approve, it sent the company a letter declaring, “Your walnut products are drugs” — and “new drugs” at that — and, therefore, “they may not legally be marketed … in the United States without an approved new drug application.” The agency even threatened Diamond with “seizure” if it failed to comply. Diamond’s transgression was to make “financial investments to educate...