An apple
That's the claim by Nikki Owen, a practitioner of neuro-linguistic programming and TV commentator who is described as Britain's leading charisma expert.
'I've long been trying to impress on people the impact our thinking has on physical appearance,' says Nikki, 49, who lives in Kent.
'Each of us has the power within ourselves to create the life we want - not just a career and all the trappings, but also our looks.'
The love/hate test: Nikki Owen devised a simple experiment to prove a more youthful appearance could be down to saying kinder things to ourselves
To prove her point, Nikki has devised a simple experiment using apples, which have a similar water content - 60 per cent - to the human body.
'Cut an apple in two, put one half in a jar, label it "love" and say kind things to it for a week,' says Nikki, aware that it sounds completely bonkers. 'Then place the other half in a jar marked "hate" and be as spiteful as you like to it.
'At the end of the week, the hated part will be in a considerably worse state of decay than the half that was the subject of your affections.'
Hundreds of women have tried this experiment and the results are consistent. Nikki's theory is based on the work of Japanese scientist Dr Masaru Emoto. He's done countless studies that suggest the molecules in water crystals could be affected by our thoughts, words and feelings, thus determining the shape of the crystals.
His tests reveal that molecules exposed to happy or loving environments form beautiful, symmetrical crystals, while those exposed to unpleasant influences are misshapen.
'When you consider our bodies are approximately 60 per cent water, too, it begins to make sense that positive feelings are going to affect our mind and bodies. Being mean-spirited can create rot and decay,' says Nikki.
So, is it really time to bin the Creme de la Mer or is Nikki's theory just a load of old mumbo jumbo? Cosmetic doctor Dr Patrick Bowler appears on TV programmes such as 10 Years Younger and is medical director of Court House Clinics.
Though he's sceptical about the the apple experiment, he does think Nikki has a point.
'In a broad sense, I agree with what she says,' he says. 'There have been many studies looking at the effects of positive thinking on the immune systems of people with diseases such as cancer. Those who are positive seem to fare much better than those who are miserable and give up.
'More work needs to be done, but it's true that if you feel positive about yourself you are likely to look more radiant and therefore more youthful. Being happy and positive is only one part of looking younger, though. Your diet, lifestyle and genetics will always play a part.'
Nikki's advice about putting the theory into practice could make you squirm. She says if we look at ourselves in the mirror and tell our reflection it looks wonderful, we can expect an almost instant improvement in our faces.
'I know this will be difficult for 80 per cent of women,' she says. 'But get into the habit of saying positive things to yourself and your complexion will be fresher because that burden of negativity will be gone.
'It doesn't matter how much you invest in getting your hair done or the latest antiageing products, if you don't think you look good, you're never going to look your best.'
Clinical psychologist Dr Helen Nightingale supports Nikki's theory.
'Clearly just saying nice things to yourself won't magically erase wrinkles,' she says. 'But you are what you think so your thoughts will always impact on your behaviour, mood, body and looks.
'If having a vase of flowers on your windowsill makes you feel happier, it'll show in your face.'
Time, then, to treat yourself to a bunch of daffs and some happy thoughts.