As soon as I'm done writing this post, I'm going next door to return the box of Trader Joe's Multigrain O's cereal I bought the other day.

It seemed like such a good idea when I saw it — perched colorfully with its identical siblings on the end cap — that I went for it, even thought I'd bought plain old regular O's at the Stop and Shop 15 minutes prior.

Both were for Joe, of course, who fulfills the kids-love-Cherios stereotype admirably. I knew he'd all those O's soon enough, and the TJ's box just shouted good tidings: Not only was it multigrain, but it promised 14 grams of whole grains per serving, 29 percent of the RDI for whole grains. (How whole grains appear in a box of O shapes, I don't know, but I'm sure they can back that up. I guess. I mean, they're marketers, not (outirght) liars.)

The package also cries out low fat in orange capital letters, on top of a list of 9 vitamins and minerals the cereal is "an excellent source" of.

So I was pretty surprised when I got home, though perhaps I shouldn't have been, that Trader Joe's Multigrain O's cereal, is a glazed sugary cereal. Sugar is the second ingredient, and brown sugar is the sixth. Every ounce has six grams of sugar.

The Stop and Shop house brand Os also have sugar, of course, but they are not glazed, and they don't, to me, taste sweet, though that's subjective and another issue entirely.

That brings up what David Katz of Yale calls the ONAAT fallacy, in which marketers boast about whatever good news they can about a product, in part so they can boast while not talking about the bad stuff.

This isn't a new phenomenon, of course. I recall my dear Mama Ruth, 15-20 years ago and already elderly then, proudly reporting that she'd bought the low-fat version of something, not realizing it was still high in calories and not what any objective person would call healthful. And, of course, the technique is as old as selling.

Katz's acronym stands for "one nutrient at a time," and the fallacy is "the false, but insidiously persistent notion, that the nutritional quality of a food, or the relevant nutrition guidance for a given patient, can in fact be gauged just that way, one nutrient at a time." That was one of his complaints about the Gary Taubes story "Is Sugar Toxic?": In his over-long, somewhat muddy, but direct rejoinder to Taubes, Katz wrote on HuffPost: "A diet can contain sugar, and specifically fructose, and be optimal for health. A diet could be low in sugar, but high in sodium or trans fat, or deficient in fiber and omega-3 fat — and be far from optimal."

Therefore, he said, it is unhelpful to speak against any one nutrient, which I don't agree with. Just because marketers will sieze upon whatever they can to make their numbers, it's not wrong to point out the potential ill effects of a substance.

What is wrong is making sugary cereal without saying straightforwardly that it is sugary cereal. If they're proud enough to make it the second-most common ingredient, they ought to be proud enough to put it on the front of the package.