Brian Wansink, PhD, knows that food fools most of the people, most of the time. Take a study he conducted at a Chicago movie theater. Unsuspecting moviegoers—most full from lunch and expecting a matinee, not a snack—were surprised to receive a free medium or jumbo bucket of popcorn when they arrived for the flick. They munched on the popcorn during the show, but what they didn’t know was that Wansink and his graduate students had filled the buckets with five-day-old popcorn. The stale snack was measured before and after the moviegoers chowed down, and then Wansink got to work.

It turns out that people given the jumbo tubs of popcorn ate 50 percent more than those who received medium containers, even though none of the participants entered the theater hungry and the popcorn was well past its prime. The findings, like everything else Wansink researches in his food lab at Cornell University, help explain something scientists studying the burgeoning obesity epidemic and type 2 diabetes have wondered about for years: Why, in the name of all that is Hostess, do we eat what we eat?

It’s Chemistry, Baby
There’s always a reason for our overeating, and usually it has something to do with our environment, our habits, or food chemistry—the science of creating addictive food that’ll have people coming back for more. Even those without a background in food science can figure out which types of foods people find most appealing. Just look around you. Fried chicken, cheeseburgers, and pizza are all high in fat. Most are high in salt, as are potato chips, bacon, and french fries. Sugar completes the trifecta, and it’s found in everything from the baked goods we so love to our coffee drinks and supposedly healthful breakfast foods. “That’s the trio: fat, salt, and sweet,” says Marcia Pelchat, PhD, a food scientist at the Monell Chemical Senses Center who studies why people crave the foods they do. “Over 90 percent of the foods that people report craving are high in fat. They could be fat and salt, fat and sweet. They could be high in protein, but fat is right there.”

Consider a Snickers bar: chocolate (fat and sugar) with peanuts (salt), nougat (sugar), and caramel (fat and sugar). The combination of tastes makes it nearly impossible to stop at one bite. “If food tastes really good, it sort of makes us want to eat more,” says Pelchat. “So if we’re eating something high in fat and sugar and salt, that will stimulate, at least for a while, our desire to eat.”

David Kessler, MD, former commissioner of the Food and Drug Administration, explains this idea in his book The End of Overeating: Taking Control of the Insatiable American Appetite when he notes his inability to eat just one M&M. The food industry, he says, is all too familiar with the trio of tastes, engineering foods with just the right amount of fat, sugar, and salt to make people chow down, again and again. It’s the idea behind the old Lay’s potato chip slogan “Betcha can’t eat just one” and Pringles chips’ “Once you pop, you can’t stop.”

According to Gail Vance Civille, president of Sensory Spectrum, a company that researches the taste, smell, look, and feel of food and advises companies on what consumers like to eat, the onus isn’t just on the food industry. “It’s more of a collusion between the consumers and the food companies,” she says. That is, manufacturers produce the foods consumers eat (and buy) most often.

Partly to blame is our brain chemistry. “The body responds to [foods high in fat, sugar, and salt] by producing sort of a high, if you will, with the stimulation of portions of the brain,” says Vance Civille. “What happens is the body then continues to seek out that hit and continues to sort of crave the types of foods and food sensory impressions that make you happy.” The scenario is similar to drug addiction, with one major difference: Quitting cold turkey’s not an option. We need to eat to live.

A Force of Habit
Food chemistry goes hand-in-hand with experience. “People crave comfort food in moments of distress,” Vance Civille says. “What causes it is that there was a point in my life where I felt safe and secure with this food around me, and therefore when I have a stressful situation I’m going to crave this food because it makes me feel better.”

This is similar to food habits, which Pelchat says also feed cravings. Eat the same breakfast day after day, and the one day you eat something different, you might crave your regular breakfast. That’s a good thing if you’re eating a healthy meal of oatmeal or a veggie omelet. But if you make a regular habit of having, say, a doughnut with your morning coffee, the routine could be just as much behind your craving as the pastry’s fat, salt, and sugar content.

Taking it a step further, Pelchat says economics may get the whole ball rolling: Foods high in fat, salt, and sugar are typically cheap, which makes people more likely to habitually eat them, which in turn drives cravings.

Blame Your Environment
Eating should be an easy process. The stomach releases a hormone called ghrelin that signals to the brain it’s time to eat. Another hormone, this one called leptin, tells the brain to stop eating when you’re satisfied. Simple, right?

Well, not quite. “As long as you only eat when you’re hungry, you shouldn’t get fat,” says Pelchat. “But the problem is that we eat in response to cues in the environment.” Anyone who has ever scarfed down a big piece of pie after a large meal knows that hunger and fullness aren’t always all that’s involved in eating. Too often, we decide when to eat, what to eat, and how much to eat based on external food cues.

“People make over 250 decisions about food a day. It’s not just whether you have a soup or salad. It’s how much salad, what dressing, a little bit or a lot, whether you’re going to finish your salad or not,” says Wansink, whose book Mindless Eating: Why We Eat More Than We Think explores how outside factors influence these decisions. “We end up being influenced by the things around us in ways that we’re not aware of. It may be the size of the plate [or] the lighting. It could be what the person’s doing next to us.”

Proximity: Consider Wansink’s movie theater popcorn experiment. Though most participants had just eaten lunch, they ate the popcorn anyway. “When things are in front of us, it matters less how much we like it than what the cue is,” Wansink says. “These cues are hugely powerful. They’re more powerful than the taste of the food and the taste of the popcorn.” That’s why participants kept eating stale popcorn.
We’ll even eat more food when it’s right in front of us than if it’s 3 feet away. (Wansink studied this, too, and found participants ate more candy from a dish on their desks than from a desk just a step away.) Scientists find we’ll eat more candies when they’re unwrapped in a jar—think M&Ms—than wrapped—such as Hershey’s Kisses.

Container Size: At the movie theater, instead of stopping when they were full, most eaters gauged satisfaction based on the size of their popcorn tub. “The size of that bucket has a huge impact on us,” Wansink says. “The size of a bucket or bowl suggests to us what we think the consumption norm is.” It’s why we eat more when served on large dishes than appetizer-sized ones.

A Clean Plate: In another study, Wansink and colleagues rigged a bottomless soup bowl and monitored how much participants ate compared with those who ate out of a normal bowl. Even though they ate 73 percent more than people whose soup bowls didn’t automatically refill, participants who received the bottomless bowl didn’t think they consumed more. That’s because both groups gauged fullness based on an empty bowl—not on how satisfied they were.

Time of Day: Even the clock plays a role in whether or not we eat, especially for those who are overweight or obese. “It’s been known for years that overweight people may be more responsive to these environmental cues for eating than normal-weight people,” says Pelchat. She describes a study in which the eating habits of normal-weight and overweight people were studied as the researchers changed the clock. When overweight people (incorrectly) believed it was close to dinnertime, they ate more than when they thought it was afternoon. The normal-weight people, on the other hand, didn’t change their eating habits based on the time.

Outsmarting Yourself
You can’t just stop eating. But cutting back on those highly palatable—yet really bad-for-you—foods will do your body good. In fact, Pelchat says, taste can change. “If you give up sugar or greatly reduce the amount in your food, after about a month your most preferred level of sweetness will go way down,” she says.

In a study at Monell, researchers put hospital patients on a low-salt diet, with half of the group able to shake salt on their food. The scientists found at the end of the study that those who had gone without added salt tolerated a lower level of sodium in their food than they had at the start. The other group’s taste preference didn’t change.

Getting to the point of literally changing your taste requires persistence. “The cravings are highest in the first week or two, and then they tend to decrease,” says Pelchat. “You just have to stick it out if you’re committed to making that change.”

Of course, you don’t have to completely give up fat, sugar, and salt. In fact, abstaining from such pleasures might even make the process harder because we tend to crave forbidden foods. “You can at least weaken some habits and cravings just by sticking to a new diet,” says Pelchat. Instead of cutting, try replacing. “You can never really get rid of a chocolate craving or a craving for french fries, but if you start eating fruits and vegetables and grilled fish and things like that, you’ll miss [those healthy foods] when they’re not there.”

Dealing with environmental cues is another issue in itself. The solution to what Wansink calls mindless eating—scarfing down food on autopilot—usually isn’t mindful eating, he says. “The solution for most people is to change our environment so that we can mindlessly eat less rather than mindlessly overeat,” he says. That may include using smaller plates, moving the candy jar off your desk, or asking for half your restaurant meal boxed up before it arrives at your table. (For more tips, see “Mindless No More,” right.)

How do we change the role food chemistry and psychology play in what we eat? “That’s a tall order,” says Vance Civille, “but I think it’s a very legitimate way to think about solving some of the issues with [type 2] diabetes. I really think that part of the solution to this is teaching children how to eat and teaching parents how to cook and relish food as . . . something that is part of the culture of our families.”