Victoria Beckham's secret diet weapon. InstagramSweetleaf

You don't have to be a big fan of Victoria Beckham to be impressed by how the 44-year-old mother of four maintains her reed-slim figure.

She has revealed that she exercises for at least two hours every day interestingly, she also swears by a flavoured liquid sweetener which you can add to coffee, smoothies, milkshakes or yoghurt to transform any food into a low-calorie, guilt-free treat.

Could this be the secret of eternal slenderness for the rest of us?

In a recent Instagram post, the fashion designer shared a picture of a tiny bottle of chocolate and caramel-flavoured liquid stevia drops and asked her legion of fans if anyone knew where she could buy them in her home city of London.

Well, Victoria, you'll have to take to the internet to buy the Sweetleaf brand, but luckily there are a couple of very similar varieties available in British stores.

Artificial sweeteners have been the dieter's friend for decades, so what makes these flavoured stevia drops particularly special?

The key, it seems, lies in their handbag-sized portability, the wealth of indulgent flavours and the fact that stevia is lauded by many as the most ‘natural' form of sugar substitute available.

Many other types of sweetener, such as aspartame, saccharin, sorbitol and sucralose, are chemically derived and can leave a bitter aftertaste, but stevia jostles for position at the top of the pile because of its natural origins (it is extracted from the leaves of the stevia plant).

With little-to-no glycaemic index (meaning it shouldn't affect blood sugar levels) and zero calories, it has become the sweetener of choice among the trendy "clean-eating" brigade.

Victoria Beckham's nutritionist, Amelia Freer recommends it ‘for use now and then for a treat', and trendy lifestyle and weight-loss guru Louise Parker (whose clients include the Duchess of Cambridge) reveals it's one of her cupboard essentials.

"I'm a huge fan," she says. "It's a great product to sweeten anything from creamy bowls of porridge to protein shakes, so you can "save" your sugars for the weekend when you're craving a glass of wine or pain au chocolat.

"I use it in smoothies or mix into cocoa powder to make sugar-free hot chocolate. You can even beat it into egg whites with cinnamon to create a coating on both sweet and salty protein-rich snacks."

Certainly, for anyone watching their weight, it is easy to see how a few drops of highly flavoured sweetness can make even the most draconian diet plan seem palatable.

Daily Mail