'Invisible' sugar is behind the soaring rates of obesity, some experts now believe. And it's not just processed foods that are getting sweeter.
January is a grey month, a burnt-out shell between streamingly festive December and "back in the pink" February, when we all feel just about OK and our bank balances skip back into the black.
It is a time of navel gazing – quite literally – when the ghost of Christmas dinner past comes back to visit. A time when we look down at our much grown waistlines in despair and think: "I'd better do something about this."
But what to do? Some of us pledge to take exercise, get on that bike and find a waistline. Others promise to give up red meat, cut out the butter and learn to say "no" to that extra slice of chocolate cake.
In short, most of us will do what we always have done when we wanted to drop some weight. We'll follow the guidelines drilled into us by successive health tsars, chief medical officers and ministers of health down the years: we'll cut our intake of fat. It is the standard course – but it simply isn't working.
So what is the explanation? According to Dr Lustig, whose new book Fat Chance: The Bitter Truth about Sugar, it comes down to a change in diets in the 1970s; a change most of us probably didn't even notice. The Seventies saw the development of foods with manipulated low-fat contents. And low-fat food, according to Dr Lustig, is making us fat.
"When you remove fat from food, it tastes like cardboard, The food industry knows that. So when they took fat out, they had to add the carbohydrate in; and in particular fructose sugar," says Dr Lustig. So as the low-fat dogma took hold, we cut out the fat and started taking on vastly more fructose. In America fructose intake (mostly in the form of high-fructose corn syrup) has increased 100-fold since 1970.
The quantity of stand-alone bags of sugar sold – stuff lingering in granny's baking cupboard – has decreased. Yet in the period from 1990 to 2000 consumption of sugar went up by around a third – and a significant quantity of that is sucrose, which is 50 per cent made up of fructose. This is what researchers mean when they refer to the rise of "invisible sugar".
It is invisible in the sense that few of us notice it but it very much exists. Take, for instance, a Volvic Touch of Fruit Lemon and Lime (1.5 litres) – how much sugar would you guess was in that? You'd be hard pressed to guess: 16 sugar cubes. Or barbecue flavour Pringles? They have 1.5 cubes. A plain bagel? 1 cube.
How have we become accustomed to sugar in just about everything that passes our lips in such a relatively short period of time? According to Charles Spence, professor of experimental psychology at the University of Oxford, we are used to it because we eat more – and we eat more because we need more. "We experience it in increasing amounts and grow accustomed to it. Think of it like eating chillies – the more you eat, the more you need to eat to feel the level of heat."
This goes some way to explaining what the writer Felicity Lawrence found when she studied fruit and vegetable production in 2007. She discovered that farmers are increasingly concentrating on producing super-sweet varieties of fruit that hitherto had been thought sweet enough. Why? Because our whole diet has an ambient quantity of sugar in it – so a sweet apple suddenly seems bland.
Fat Chance: The Bitter Truth about Sugar by Dr Robert Lustig, priced £13.99, is published by Fourth Estate