A girl sits down to a plate loaded with pizza. A boy gets a few baby carrots. Immediately, both kids’ brains start taking stock what’s in front of them. Consciously, the kids might be thinking “Yum” or “Yuck.” But their brains are also processing how much food is there — a feast, or just a nibble. And they’re cataloguing whether it contains a lot of calories per bite or just a little. Different parts of the brain are responsible for handling these two questions, a new study finds. The answers they come up with could limit the diner’s self-control.
Studies show that the more food there is on a plate, the more someone is likely to eat. Nutritionists call that the “portion size effect.” It doesn’t matter what kind of food it is. It also doesn’t matter whether the diner is young or old, male or female, alone or in a group. The bigger the portion, the bigger the appetite.
Laural English is a nutritionist at Pennsylvania State University in University Park. She knows that many eating habits that kids pick up in early childhood will still be there when they are adults. So she and her colleagues wanted to find out what happens in the brain when a child sees a large portion of food. Knowing what drives kids’ eating habits might help families create healthier lifelong habits.
Calories are a measurement of the amount of energy contained in food. English and her team also wondered if it matters whether a large serving is packed with calories (such as pizza), or less energy dense (such as carrots).
“When you’re sitting down to eat a meal, you don’t appreciate all the different impacts or cues in front of you,” notes Kathleen Keller, who helped run the study. “Size, smell, taste, the way food is presented — all have an impact on what the brain perceives and also what you eat,” she says. The new study is the first to look separately at how the brain reacts to portion size and the calories in it, she says.
What happens when the brain perceives a meal?
The research team recruited 36 children to take part. All were aged 7 to 10. Half were boys, half were girls. Nearly all had a healthy weight. To make sure that all of them were hungry, the researchers asked the kids not to eat for two hours before the study began. When kids arrived, the researchers had them climb into a magnetic resonance imaging (MRI) machine. It looks like a giant donut standing on its side, with a bed sticking out of the center. It uses magnets and radio waves to map the flow of blood in someone’s body.
Each child had to lay down on the bed with his or her head inside the donut. Staying very still was important. Moving one’s head more than the thickness of a dime would ruin the scan, notes Keller. To help avoid that,…