(UPI) -- U.S. researchers say sugar does not appear to have a metabolic boost for self-control.

Psychological scientist Daniel C. Molden of Northwestern University in Chicago and colleagues said many had thought self-control relied on carbohydrate metabolism -- people deplete their carbohydrate stores as they exert self-control, making it more difficult to exert self-control until the stores are built up again.

Molden and colleagues decided to test this model in a series of four experiments in which participants' baseline glucose levels were assessed prior to performing tasks that required self-control.

The researchers found no evidence for a relationship between self-control and glucose metabolism.

"Follow-up studies indicated that participants who rinsed their mouths with a carbohydrate solution showed improved self-control, despite the fact that they didn't ingest the solution and there was no observable change in their blood glucose levels," the study authors said in a statement. "These findings suggest a motivational as opposed to metabolic mechanism for self-control."

The study was published in the journal Psychological Science.