When a reporter asked Oprah Winfrey what makes some celebrities act like jerks, she said, "If you were a jerk before the fame, you just become a jerk with a bigger spotlight. Whoever you are really comes through."

Jerks are like that, and so is jerky — beef jerky, that is.

It's been around for centuries. The Conquistadors called the Incas' dried, smoked llama "charqui," from their word "ch'arki"; in North America, it became "jerky.”

But lately it's gotten a bigger spotlight, and what Johns Hopkins researchers have brought into focus will jerk you to attention.

Many processed meats, including most jerky, bacon, hot dogs, salami, and sausages, are preserved with nitrates. The Hopkins scientists' first study with mice found that after a few weeks on a diet laced with added nitrates, the animals developed mania-like hyperactivity.

That got the researchers wondering about the chemical's effect on human behavior.

So their recent study looked at 1,000 people with and without psychiatric disorders. It showed that over a 10-year period, those folks who had been hospitalized for mania were 3.5 times more likely to have eaten cured meats as the group without a psychiatric disorder.

One theory: The nitrates alter gut bacteria and that affects neurotransmitters (they're not just in your brain), leading to changes in mood, perception, and behavior.

We've long warned you off processed meat, because studies linked nitrates to some cancers, and the meats' fat content is heart-stopping.

Now there’s another reason to dodge added nitrates: they'll jerk your mood around.