McDonald's (NYSE:MCD) is blowing it.

After trying to convince consumers that its food isn't that bad, the king of the fast-food burger clowns now says that its fries, um, aren't as healthy as once thought. (Cue sarcastic voice.) Really?

The problem is with labeling. For months, McDonald's has claimed its fries were OK for those with food allergies because they didn't contain gluten or wheat or milk allergens. But that, apparently, wasn't quite true. According to the most recent ingredients list, McDonald's fries contain both wheat and milk. Whoops.

I'd chalk it up to an honest mistake, yet McDonald's never announced the labeling gaffe, and as such, I'm inclined to believe the company still doesn't take its mistake seriously. Indeed, a spokesperson told the Associated Press that McDonald's processes the fries to strip out offending proteins, which means, she says, that "those who have eaten the product should be able to continue to do so without incident."

My experience is that any exposure to an offending food, even in small doses, can have an impact -- from skin irritation to anaphylaxis. As such, I can find no good reason why McDonald's wasn't a bit more forthcoming.

Less important, but still significant for investors, is what this all means for the burger flipper's healthy choices strategy. Poor disclosure won't win customers. And that ought to be worrisome: Today, 11 million Americans suffer from food allergies, 2.2 million suffer from Celiac Disease (a disorder that prevents the digestion of gluten), and between 30 and 50 million are lactose-intolerant. In short: The health nuts make up a powerful market. But they expect to be dealt with honestly. Keeping an accurate ingredients list is the least they will expect. Are you listening, Ronald?

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Fool contributor Tim Beyers can't get enough of his three kids, two of whom have food allergies. Tim didn't own shares in any of the companies mentioned in this story at the time of publication. You can find out what's in his portfolio by checking Tim's Fool profile. The Motley Fool has an ironclad disclosure policy.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.