The fascinating reason why you can't resist a glass of wine in the evening

There's a reason why many of us just can't resist a glass of wine or a chocolate snack in the evening. 

Scientists say they have the "strongest evidence yet" that willpower is a limited resource, the reports.

They claim attempting to resist temptation early in the day means we're far more likely to lack self-control at night - an effect known as "ego-depletion".

Researchers from Texas A&M University carried out two experiments to prove that the ego-depletion effect exists.

In the first experiment, 657 students were asked to either write for five minutes about a recent trip or write about a trip without using the letters 'A' or 'N' – which required more self-control.

Following this, participants completed one of two versions of the Stroop task - either they had to name the ink colour of colour-denoting words, such as the word 'red' written in blue ink, or the ink colour of emotional or neutral words.

Ignoring the meaning of colour words and focusing on ink colour takes a degree of self-control.

Results showed that participants who completed the more difficult version of the writing task responded just as fast, but made more mistakes on the Stroop tasks than the control group.

In their study, which is publicly available on the PsyArXiv preprint website, the researchers, led by Dr Katie Garrison, wrote: "This pattern represents unambiguous evidence for poorer attention control under ego depletion."

In the second experiment, 350 participants completed either the easy or difficult writing task, and then the Attention Network Test.

This test involves repeatedly indicating the direction of arrows on a computer screen, while ignoring the direction of other, distracting arrows.

Results showed that participants who completed the harder writing task made more errors on the Attention Network Test.

Again, this is consistent with the ego depletion theory. 

While the reason why ego depletion occurs remains unclear, the researchers now plan to investigate this further.

They added: "The evidence for an ego-depletion effect on attention control reported here should encourage explorations into mechanisms driving the effect. 

"For instance, does depletion result from a drop in resources, a strategic conservation of resources, or a motivated shift away from have-to goals toward want-to goals?

"The answer remains to be seen, but the current experiments provide new evidence that this is still a question worth asking."

This article was first published on Daily Mail and is republished here with permission.