It starts with a single potato chip. After some rapid-fire munching, you find your fingers coated in oil and salt. Before you know it, you’ve devoured an entire bag of chips while you're sitting in front of the TV.

Or maybe your food of passion is ice cream or pizza. Regardless, it’s caloric overload when you've polished off an entire large container all by yourself.

Mindless eating becomes a habit when people shovel food into their mouths, blissfully unaware of how much they’re eating, how full they feel and what the food actually tastes like.

Here’s a suggestion from one study conducted at the University of Southern California: Switch hands.

People who snacked using their nondominant hands reduced about 30% of their total intake, compared with those using their dominant hands, according to the study, which was published online in the journal Personality and Social Psychology Bulletin.

“If people disrupt the physical sequence of action that is in automatic eating, that’s one way to gain some control,” said David Neal, who had been an assistant professor in psychology at USC at the time of the study. Since then, he has left to start his own company, Empirica Research.

For the study, Neal and his colleagues gave each participant a bag of popcorn - some were stale popcorn (popped a week ago), and others were fresh (popped less than an hour ago).

They sat in a dark movie theater and watched several trailers while they were within convenient reach of their popcorn bags. In questionnaires, they indicated whether they habitually ate popcorn in the movie theaters or not.

After the participants left, researchers weighed the popcorn bags. They found that the people who indicated that they regularly ate popcorn during a movie screening ate about 63% of the popcorn bag - regardless of whether it was stale or fresh.

“If you are the sort of person who bought and ate popcorn a lot in the past, as long as you’re in the environment, you continue to eat the food even when it’s stale and horrible,” Neal said.

Being in the dark movie theater environment with popcorn at easy access seemed to trigger an automatic eating habit, he said.

“People believe their eating is controlled by internal preferences,” he said. “We think how much we eat is guided by how hungry we are or taste of the food options. But in reality, that’s not the case. The environment plays a big role.”

So the researchers altered the environment. Instead of a movie theater, they set up a dark meeting room with music videos projected on a screen with popcorn at the ready. The participants didn’t eat as much popcorn when their environment changed.

For the final study, they asked participants to use their nondominant hand if they chose to eat the popcorn inside a movie theater.

The amount of stale popcorn eaten by habitual popcorn lovers dropped about 30%. The amount of fresh popcorn eaten also dropped, but the difference was slight.

“It’s inconvenient and disruptive to eat with the nondominant hand, but that effect is much stronger when the food is horrible,” Neal said. “It suggests it’s not just inconvenience. It makes you think, ‘Is there a value of what I’m doing? Does this taste good? Am I hungry?’ If the answer is no, you stop eating.”

The researchers borrowed this trick from neuroimaging studies that have shown that people’s habits are disrupted when they’re asked to perform tasks using their nondominant hand.

Dining out at a fancy restaurant using your nondominant hand might make for a really clumsy and awkward meal. So, this advice might be more practical when you’re sitting in front of the TV, where your snacking could get out of control.

“The general idea is that relying on willpower and self-control is often not very effectual,” Neal said. “It doesn’t get people to change health behavior.”

Try changing your environment that triggers mindless eating behaviors, he suggested. You could try switching to smaller plates and utensils to eat less, stashing junk food out of reach in shelves, or you could try eating with your left hand (if you’re a righty) or your right hand (if you’re a lefty).

But this tip may not work out if you’re ambidextrous.