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Why being full makes you want to eat more

Cleaning your plate and stuffing your stomach this Thanksgiving may just make you hungry for seconds, and a new study explains why.   

Researchers from the University of Vermont found that if fullness becomes associated with getting food, we may feel hunger even when we don’t physically need food.

So all those times your mother told you to clean your plate if you wanted dessert may have built a bad mental habit: the more I eat, the more tasty foods I can get. 

They also found that responses to hunger or fullness were learned more quickly than other cues, making the bad habit of eating after you’re full even harder to break. 

According to the study, this psychological conditioning helps to explain why we may go back to over-eating, even after a successful and effective diet.

If you’ve been conditioned to think that more, tasty food is coming when you’re full, you could actually wind up feeling hungry after eating a full meal

Dr Mark Bouton and Dr Scott Schepers taught 32 female rats that they would be given tasty treats if they pushed a lever while they were full, but not if they pushed it while they were hungry. 

After they’d been conditioned, the rats pushed the lever far more times if they were already full than when they were hungry. 

This showed the researchers that the learned pattern of getting food when they were full could actually be more powerful than the physical feelings of fullness or hunger. 

Previous research has found that hunger can be cued by external cues and conditions, not just internal ones, like the feeling of an empty stomach. 

This study elaborates on that, finding that external cues – the conditioning of the rats – can lead to the internal feeling of hunger too, even when we are full. 

Dr Gary Foster says that this is all just a result of standard conditioning. 

‘If you relate the behavior of eating to anything else, it becomes a habit,’ he says. 

We can’t know for certain if the rats in the experiment actually felt hunger, but we do know that they were conditioned to think they would get more, enjoyable foods under certain circumstances, in this case, when they had already been fed. 

For humans, any behavior can become ‘coupled,’ with eating, Dr Foster says. 

The more behaviors that get coupled with eating – getting home from work, going to the movies, getting in the car – the more times you might find yourself craving a snack.

Weight Watchers’ Dr Gary Foster’s tips for avoiding over-eating 

  • Uncouple eating from other activities. Try not getting popcorn next time you go to the movies, or drinking a sugary coffee drink just because you’re driving.
  • Make eating the event.  Enjoy the meal in and of itself, savor the taste, and pay attention to how sated you are.
  • A good test is to think about food like a friend. Would you pull out a book or watch TV when your friend came over? Then you should give your meal the same attention. 
  • Enjoy the holidays, know you’re going to eat more than usual, but make sure you plan to eat the things that are really worth it. Cheese and crackers may happen every day, but grandma’s sweet potatoes don’t! 

‘It’s not because people are hungry when they get in the car, or go to the movies,’ says Dr Foster, ‘it’s that eating becomes a secondary behavior, it has to go along with those activities.’ 

But that coupling can be ‘extinguished,’ to use the experiment’s term. 

The difference between humans and the rats in the experiment is that the rats were controlled and trained to associate food with times when they were full. 

‘We can do that in ways that are our own choice,’ says Dr Foster. 

He says it’s best to limit the number of things we associate with eating.

Instead, ‘make eating an event valued in and of itself. Taste the food, enjoy the experience,’ don’t give in to your weeknight tradition of Netflix and Chinese.

Avoiding over-eating is all about being mindful, he says. ‘If you go into a meal in a mindless, unplanned way, you’re more likely to overeat and be triggered. You won’t get that much pleasure, but still get the downside of over-consumption,’ he says. 

At the holidays, the meals often are the main event, and over-eating can feel like a part of the experience, an obligation. 

‘At Thanksgiving, the tradition is that I’m going to eat more than other days. No matter what, I’m going to have the pumpkin pie, because that’s the tradition,’ Dr Foster says. 

So instead, he says to eat what’s worth it.

‘It’s about progress not perfection, so [at the holidays], expect to eat more than usual, but pick your spots,’ says Dr Foster. ‘Do you really want to waste your time on cherry pie, if pumpkin pie is your thing?’