We have a limited supply of willpower, study suggests

Seth Wenig / AP file

Self-control is a limited commodity that runs low as you use it. So once your pool dries up, you'll struggle when faced with temptation, finds a new study in the Journal of Consumer Research.

Researchers asked 16 people to perform self-control tasks while being monitored by an fMRI scanner. During the first session, people were assigned to either a demanding mental task or easier task. Two weeks later, they swapped tasks.

The results: Brain scans from the first session showed promising activity in both the participants' anterior cingulate cortex (ACC)--an area that deals with decision-making--and dorsolateral prefrontal cortex (DLPFC), an area that helps manage self-control.

But after the second session, those who were exposed to the demanding task first showed less activity in their DFPFC. Simply put, "if you exert a significant amount of self-control at one time, you'll have a hard time exerting it later," says lead study author William Hedgcock, Ph.D., a neuroscientist at the University of Iowa.

Let's say you're sitting in front of a plate of brownies at work, but you resist because you're on a diet. Hedgcock's research shows the next time you're faced with sweets--whether it's later tonight or two days from now--you'll be more likely to cave. Why? Hedgcock believes it's because your self-control is like a muscle: If you use it extensively in the short term, it will wear out and become exhausted. And time is really the only thing that helps it recover.

To prevent your self-control engine from running out of fuel, use your resources more wisely, or make less drastic choices, says Hedgcock. That's easier said than done, but here's an example: If you're on a diet but still craving something sweet, opt for a smoothie over a large sundae, rather than caving or withholding completely.

That way, you satisfy your craving and exercise some self-control, but also refrain from overworking it, says Hedgcock. (For more tips on keeping your mind sharp, discover 27 Ways to Power Up Your Brain.)

More from Men's Health: