For years, academics across the world have studied the effects fast food advertising has had on children and adolescents. With nearly 1-in-5 school-aged children in the United States qualifying as obese, these studies aim to figure out how TV commercials, product placement and the new frontier of digital marketing are leading to unhealthy lifestyles.

But let’s say you watch a commercial for a Big Mac. Do you immediately drive to McDonald’s and order the 563-calorie bomb? Not necessarily. However, fast food marketing seeps into your brain in a way you may not realize.

At the University of Michigan, associate professor Ashley Gearhardt runs The Food and Addiction Science and Treatment (FAST) lab, a simulated fast food restaurant that uses neuroimaging to study this sort of stimuli. She’s currently conducting a study on 180 teenagers and what happens in the striatum—the reward section of the brain—while viewing the ads, and how the ads can get “under the skin.” She showed teens three kinds of commercials: unhealthy fast food, healthier fast food and a control commercial for cell phones.

“When teenagers are seeing fast food commercials, it really seems to be activating reward centers of the brain more effectively than other types of advertisements,” Gearhardt told HuffPost about her preliminary findings (a published paper is forthcoming). “The teenagers that are showing this greatest reward activation of the brain seem to be at greater risk in gaining weight over time. It’s hard for people to defend against because it’s not a conscious process.”

She further explained that seeing something like a Big Mac on the screen doesn’t make you crave one—it makes you want everything in that category, and it’s happening on a biological level.

Read the full article at the HuffPost.