It all comes down to willpower, right? Muster the resolve to skip dessert, and you have a shot at losing that spare tire. Succumb to your temptations, however, and it's a sign of weakness.
But is it that simple?
A study in Psychological Science suggests that our inability to resist that chocolate cake isn't necessarily of weak willpower is weak but worn-down resistance, because our ability to overcome temptation is actually reduced at the same time that the power of the temptation increases.
In the study, participants first underwent an exercise meant to exhaust their willpower: They watched a seven-minute documentary on Canadian bighorn mountain sheep. That documentary on its own didn’t exhaust people’s willpower significantly, of course. But the distracting words scrolling across the screen did. Half the participants were told to watch the documentary and read the words as they scrolled in front of their field of vision only if they wanted to. No significant willpower test there: If you are curious what the words are, you look at it. If not, you don’t.
But the other half of the participants were instructed specifically not to read the words—they were told to maintain their focus on the sheep and nothing but the sheep. Seven minutes of ignoring scrolling words while watching sheep? It's exhausting just to think about it.
And willpower exhaustion was a key element of the study, because previous research has shown that willpower is depletable. Exert it for seven minutes and you have less to draw on in the near future.
Which leads us to part two of the study: The researchers placed these participants in an fMRI machine and flashed pictures of deliciously unhealthy foods. They wanted to see which parts of people’s brains lit up in front of these tempting delicacies. (It should be noted that all the participants in this study reported trying to lose weight, and all had fasted before the study which probably means their willpower was already somewhat depleted before they entered the lab.)
Here's what happened: The fMRI images revealed differences across the two groups of participants in their ability to resist temptation. They found neurologic evidence of depleted willpower among the people who spent seven minutes not reading those pesky words. But that's not all they found: Those people whose willpower had been relatively depleted also showed increased activity in regions of the brain associated with “Q reactivity”—basically, the activity in these brain regions revealed that the food pictures looked tastier to depleted participants than it did to non-depleted ones.
Think of it this way: You’re on a diet. You have a tough day at work, and an awful commute back home (where it took all your remaining willpower not to instigate a road rage incident with the guy who cut in front of you on the highway) and now you open up your fridge to have a healthy salad. But then you spot a tempting container of macaroni and cheese. Not only are you too exhausted to resist the temptation, but the macaroni and cheese actually strikes you as something that would be so delicious to eat.
Under such conditions, your spare tire isn’t going anywhere.
Previously posted on Forbes.com