Huzzah! You’ve got the impetus to make a change in your life! But what to do first?

Eat really healthily? Start a new exercise programme? Quit smoking? Start saving money? Drink less? Master astrophysics and solve the photon underproduction crisis? How about doing them all at once!

No, you dafty. This is why most New Year’s Resolutions fail. Sure, you may feel all gee’d-up and ready for anything on the first of January, but if you’re trying to change four separate things all at once, you’ll get overwhelmed. And what happens when you get overwhelmed?

This is particularly important if you’re trying to eat more healthily or at a calorie deficit so you lose weight. One of the most fascinating things that has emerged recently in psychology is the finding that willpower is a finite resource. Professor Roy Baumeister at Florida State University has named this phenomenon ‘ego depletion’ and it is stunningly consistent in how it works.

In experiments conducted by him and his colleagues, people were made to sit alone in a room next to a plate of freshly baked cookies with the smell wafting over them, and either allowed to eat as many cookies as they wanted, or to resist the temptation and eat nothing. The test subjects were then taken to another room and given puzzles to do that were technically impossible to complete. Those who had been allowed to eat the cookies persisted at the puzzles for far longer than the test subjects who had been denied any snackage.

That’s right, sarcastic cat. It turns out that willpower can be drained by doing tasks that need it, leaving less available for other tasks. Hence why when you’ve had a stressful day at work involving kowtowing to your boss’s idiotic demands, you feel much less inclined to go to the gym later and much more inclined to neck a bottle of cabernet sauvignon and a giant pizza. There’s only so much willpower to go round and you can’t use it for everything.

‘But Hel,’ I hear you cry, ‘ isn’t there some way to build your stores of willpower back up again?’

I’m glad you asked, person reading this blog. There is indeed a way to build up willpower when it’s been depleted but it’s bad news for dieting. Basically, you have to eat something.

Yeah, it’s what Baumeister calls the ‘dieter’s catch-22’. Willpower is fuelled in the body by glucose – your blood sugar levels. If your willpower is low, a glucose hit from having a snack will bring it back up again. Cut down your diet and your glucose levels drop, and with it your willpower. But you need willpower to diet! Hence, the dieter’s catch-22.

So what can you do if you want to eat healthily? Are we basically all doomed to be fatties once we’ve put the weight on? No, not if you’re careful. Just don’t blitz your whole lifestyle all at once – you need to concentrate your willpower on forming good habits within one area and one alone. And the best way to conserve your willpower if you’re trying to diet is to structure your life so that eating healthily is easy.

Pack your lunches before you go out rather then running the gauntlet of the chocolate aisle in the supermarket later. If you’re eating at a restaurant, have an idea of what you’ll order in advance so you can eliminate the need to expend precious willpower on deciding once you get there. And start small and slow – you really don’t have to be Superman/Superwoman right from the get-go.