It’s a funny thing we humans often do—eating when we are no longer hungry. I’ve been around children who say they are “full” and want to stop eating at dinner, and then ask for ice cream or chocolate a few minutes later.

And we’ve all been eating at a restaurant where the waiter asks if we have “saved room for dessert?” We never do, yet we often eat it anyway. We don’t have a dedicated “dessert stomach.” We are rarely legitimately hungry at the end of the main meal at a restaurant.

We’ve got two systems for controlling our behavior: the thoughtful, conscious system, and the procedural, habit system. Only one of the two can be in charge at once. If we are distracted, bored or sad, we are often controlled by the habit system to use proven ways out of those states. Habits are neither good nor bad—they are simply a way of streamlining common behaviors to make the choice easier to save mental energy. The problem is that many of the habits we develop around eating are unhealthy and unwise.

Your Early Years

Eating is a learned behavior. Perhaps your parents gave you food to calm distress when you were a child, which taught you that unhappiness is a reason to eat. These actions and patterns, explains Bee Wilson, author of First Bite: How We Learn to Eat, “teach us to silence our sadness with sugar,” and start very early in life.

Knowing how much to eat is something that infants are better at than older children or adults. Until age three, children have a remarkable ability to stop eating when they are full. Portion size doesn’t matter. They will eat until they aren’t hungry and then stop. After that age, we get worse at eating the right amount due to social pressures and learning. When it’s your birthday, you aren’t allowed to not want cake and ice cream.

Win or Lose, It’s All the Same

We are conditioned to use excess calories and junk foods to celebrate. One study was able to trigger celebratory binge eating by putting subjects in a good mood simply by watching a short (2.5 minute) heart-warming film. Subjects consumed 100 calories more of snack foods than a control group that watched a boring film. That’s a lot of calories for a relatively small boost in positivity.

Too many parents use treats like fast food or ice cream to celebrate a great day—and use the same foods to soothe a child’s sad feelings on a bad day. This lays the groundwork for consuming junk foods during every emotional high or low in life, irrespective of how hungry you actually are.

A Dessert Stomach?

Why do we get totally full from dinner, but still “have room” for dessert? “Sensory Specific Satiety” is why. As we eat a certain food, our hunger for that particular food declines, but our hunger for other, new foods remains fresh. The original evolutionary purpose of this was to promote a varied diet, back when our diet was less varied and we would have to work harder or travel farther to get variety. It’s created a mess now—you get kids who say they are full, then immediately ask for chocolate and you field questions from restaurant staff about how much room you saved for dessert.

It’s All in Your Head

The ventromedial prefrontal cortex (VPFC) is the part of your brain that activates with anticipation of reward—for example, food is on the way when you are hungry. Once you are full, VPFC activity is diminished, making you less interested in the food. However, once you’ve created a habit (like eating while watching TV or at the movies or when we are sad), VPFC activity is not diminished when you are full. You can thus still feel an anticipation of reward when dessert is on the way—even when you are “stuffed” at the restaurant after eating the main meal.

The habits we most often develop when it comes to eating are not great. Through learning, we crave sweets after a meal (yes, this is a learned response and not one that comes naturally). We keep picking at food in front of us after we are full just because it is in front of us. We clean our plates because that’s what we were taught to do. We eat more than we want or need of a given food because we love the way it tastes. And we eat cake and ice cream at our birthday party and we cave to pressure to eat it at others’ parties, even if we are not hungry.

From our evolutionary biology, we are driven to go after what is most accessible and easily available—a habit we still have to this day. Dopamine rises with anticipation when rewards are just around the corner. Dopamine’s attraction to the immediate distorts perspective we could have acquired with our more advanced cognitive abilities. So we soothe our sadness or boredom with a quick hit of junk food at night instead of listening to what our bodies really need, and what is connected to our long-term needs and goals.

A quick note about dopamine, which is often incorrectly identified as a “pleasure” neurotransmitter. It turns out that the intense pursuit of goals like sex, heroin and cheesecake has a lot more to do with desire than with pleasure. This is a critical distinction. Wanting something is not the same as liking something, and there is more space in our brain devoted to wanting than to liking. Pleasure is a dessert, a flash in the pan. Desire is what gets us moving…dopamine is the fuel of desire, not fun.

Be Your Own Boss

Here’s some good news: It’s all up to you. Bring more awareness to what your body is telling you. Listen to signs of fullness and retrain the brain by changing your habit patterns over time.