When trying to lose weight have you found yourself sneaking visits to the cookie jar despite a promise to yourself that this time it wouldn't happen? Well a new study suggests a better strategy is not having cookies in the house in the first place. Avoiding temptation appears to be more effective for self-control than willpower, especially for very impulsive people.

"Precommitment," defined as "the voluntary restriction of access to temptations," is a "more effective self-control strategy than willpower," say researchers, from the Universities of Cambridge in the UK and Dusseldorf in Germany, in a report published online this week in the journal Neuron.

Another example is saving for the future. Precommitment is locking your money away in a savings account with stiff withdrawal penalties, or cutting up the credit card. The study suggests this is likely to work better than promising yourself you won't touch the money in the regular bank account, or you won't use the credit card.

Lead author Molly Crockett, who worked on the study while at Cambridge and is now at University College London (UCL) told the press:

"Our research suggests that the most effective way to beat temptations is to avoid facing them in the first place."

Brain scans used to test willpower

The researchers compared the effectiveness of precommitment versus willpower in healthy male volunteers while using fMRI (functional magnetic resonance imaging) to examine the brain mechanisms involved.

They gave the volunteers a series of options where they had to choose between a "small reward" (a mildly enjoyable erotic image) that they could have straight away, or a "large reward" (extremely enjoyable erotic image) that they would have to wait for.

(This is reminiscent of the famous marshmallow experiment - one now, or two later? - that tested impulse control in preschoolers 40 years ago and was recently revisited by researchers from the University of Rochester in the US.)

The researchers chose to use erotic pictures as the rewards in this study because they are instantly rewarding at the time of viewing. Thus they could monitor what was happening in the volunteers' brains in real time.

Money, for example, was not an option, despite the strong effect it might have, because the reward is not instant, the volunteers would only be able to reap it when they left the lab.

For some of the choices the volunteers could have the small reward at any time and they had to resist it in order to opt for the larger reward, which would be on offer later.

For other choices, the volunteers had the option to precommit: if they did this they would not have the continuous temptation of the small reward being available while they waited for the larger one.

During these various experiments, the researchers monitored the volunteers' brain activity as they made their various decisions.

The results showed that the volunteers, especially the more impulsive ones, were more likely to get the larger reward when they used precommitment than when they used willpower (removing the temptation of the small reward altogether worked better than trying to resist it).

Brain connection between willpower and thinking about the future

When they looked at the brain scans, the researchers found that frontopolar cortex, a brain region that is involved in thinking about the future, was active in precommitment decisions.

But what was also interesting was that when the frontopolar cortex was activated during precommitment, it communicated more with another brain region that is important for willpower, the dorsolateral prefrontal cortex.

Co-author Tobias Kalenscher, from the University of Dusseldorf, where he specializes in looking at the neural and mental underpinnings of choices, says the findings are exciting because they suggest there is a brain mechanism for precommitment.

Thinking about the future appears to engage a region that is already connected with a region essential for willpower, and perhaps this is what guides behavior toward precommitment.

The researchers hope their discoveries open the door for future studies to better understand why we succeed and fail in self-control.

Meanwhile, leave the credit card at home and wheel your supermarket trolley straight past that cookie aisle...