My first thought was, 'Oh, here we go again. What is it this time? Grapefruit? Coconut? Only eating things that begin with a P?' An editor at a women's magazine asked me to test-drive the 'hot new diet' that 'everyone is talking about'. 'It's supposed to be brilliant - people swear by it.'
Yes, like we swore by (and then at) the Cabbage Soup Diet, the Hay Diet, the Blood Group Diet, the Lose Yourself Up Your Fundament Diet ... but then something crumbles. A little voice within bleats this might be The One. There is something hugely provocative about the possibility of losing weight. And so here I am on the GI diet - the red-hot, right-now, tell-your-friends regime.
Like most women, I'm a pushover when it comes to dieting claims. Why else would we spend £2 billion in the UK each year on slimming aids and diet foods, but still lumber around with a 23 per cent obesity rate ? Why else would 12.8 million Britons be dieting at any given moment, 60 per cent of whom are on a specific programme carrying medical or celebrity endorsement?
We're suckers for it, saps for any old spiel that the colossal slimming industry can throw at us. Spin us another yarn about stunning inch loss or amazing celebrity shrinkage, and we'll buy it. A £95 unguent to eliminate cellulite? I'll take three, thank you. A mystery metabolic pill that promises to turn you into Kate Moss ? Mmm, yes please. A cauldron of bubbling vegetable debris, boiled for weeks and then decanted into Tupperware for the trip to work? Yes, I did the Cabbage Soup Diet like everyone else. There was a moment back in 1996 when every workplace in the land reeked of sprouts . Not that it deterred us. We'll go to any extremes to diet, as long as someone genuinely thin tells us it works.
That's why, for a second at least, the latest fad diet to hit the headlines seems almost reasonable. It's Liz Hurley's absurd 76-Bites-a-Day diet, which leaves her 5'9" frame weighing a wafer-thin 7.5 stones. According to hubbub, she dines on a nursery plate, with doll-sized cutlery to make her portion-controlled meals appear larger . Silly mare, I say. But (here comes that voice again), she does look great in Versace...
These days, diets are like shoes or handbags. Each season, another one comes along to turn our pretty heads. Who wasn't on the Atkins last year, hands up? And now, the whole no-carb fad is dead in the water . It is possible that we would have tired of Atkins anyway . But, let's be honest here: the Atkins programme was all but impossible to maintain. It required absolute discipline, a steely determination to face bacon and eggs each morning; a couch potato with a sweet tooth had no hope. Until, that is, the GI diet arrived.
'It's new! It's safe! And it works!' came the fanfare a few months back. GI is a lean, mean fighting machine of a diet, already with its own line-up of slimline celebs, including Naomi Campbell, Kim Cattrall, Kylie Minogue and the Clintons. Between you and me, this really could be the Big One. The bottom line, for me at least, is that a pair of jeans two sizes smaller cannot lie (I am now the proud owner of a brand new pair of size 10 low-rise denims that fit).
I am 18 pounds thinner than I was at Christmas. Which is about the weight of a full-grown Jack Russell. Friends grab me by the wrist and bark greenly, 'What have you done?' Who wouldn't want a piece of that? The GI diet is based around foods that release sugars slowly into the bloodstream, supplying a steady supply of energy with no unruly peaks and troughs. Carbohydrates are the ones to watch here - since fats and proteins have little immediate effect on blood sugar. But not all carbs are created equal. The fundamental idea is that porridge, pulses, whole-grains and other hippie comestibles eliminate the hunger pangs born of sugar lows; they keep you satiated for longer, leaving you less open to the pernicious call of the fridge.
Dr Jennie Brand-Miller, professor of human nutrition at the University of Sydney and among the first to popularise the approach (in her native Australia she is known as 'GI Jennie'), explains why it works:
'We know there's no single magic bullet to losing weight. But this is effective for controlling the appetite - which is the key to weight loss. If you're hungry, with intense cravings which are a feature of a conventional low-fat diet, these glycaemic spikes and troughs will signal to the nervous system to stock up on fuel.' And what do you most fancy when you hit a sugar low? Exactly those chocolate Hobnobs which got you there in the first place. Eliminate the roller coaster and, hey presto, you eat less. You lose weight. And you buy size 10 jeans.
The speed at which a food is digested is measured by the Glycaemic Index, which scores glucose at 100 and rates other foods against that number (an apple, for example, scores 38). Refined, highly processed, sugary foods, broadly speaking, have a high GI. Consume them and your blood sugar level will leap and your pancreas will respond by releasing insulin.
Now, insulin is the villain. Its business is to reduce the level of glucose in the bloodstream by diverting it to body tissues for immediate use, or by storing it as fat. It also has the weighty responsibility of inhibiting the conversion of body fat back into glucose for the body to burn (a hangover from our feast-or-famine cave days).
The point is that insulin not only helps the body accumulate fat, it also guards against its depletion. In short, it's Enemy Number One. If you want to lose weight, it is crucial to maintain low insulin levels. There are clear similarities with a conventional calorie-controlled diet (eat less food, and you'll consume fewer caloris ... eat less sugar, ditto), and indeed with Atkins, who dubbed insulin the 'fattening hormone' and rightly proposed that refined carbs are the core of the West's growing obesity problem.
The difference is that the GI diet encourages the consumption of slow-burning carbs - the things that keep you fuller longer - together with health-giving, antioxidant-rich fruit and veg. The upshot is a manageable, varied diet that won't clog your arteries, kill your kidneys or rot your breath.
'It's the advice we've been giving for the past 10 years, but with these added labels of high and low GI,' says Claire MacEvilly, a nutritionist at the MRC Human Nutrition Research laboratory in Cambridge. But it's the labels that make the difference, darling. It's the labels we love. There's nothing like a new set of labels to keep the dieting classes happy.
Except the GI diet really is nothing new. Its scientific basis was established by Dr David Jenkins, professor of nutrition at the University of Toronto, some 25 years ago during his investigations into appropriate foods for diabetics. ('Things take time,' says a typically laconic Jenkins from his laboratory in Canada.) Hundreds of clinical studies have since proved the value of GI, and it has been huge in Australia (thanks largely to Jennie Brand-Miller) for more than a decade.
Interestingly, it is a close relative of the later stages of the South Beach Diet, and is almost identical to the Montignac Diet. But in Britain, until recently, we have all but ignored the idea. Why should this be? And, crucially, why are we suddenly all over it like syrup on waffles?
Entertainingly enough, it's all down to spin. As we all know, there's gold in slimming. Great kingdoms of cash. Atkins Nutritionals, for instance, of which Robert Atkins owned 80 per cent, sold for over $500 million in 2003.
What's interesting about the GI diet, and what probably stalled its progress, is that it belongs to no one. The rights don't exist. If, after a leisurely read of OFM over breakfast, you fancy slinging together a few lentil recipes and some cod science about blood sugar levels, there's nothing to stop you from publishing your very own GI manual. 'GI is a concept,' says Jenkins. 'We have contributed, and continue to contribute ...we do not believe anyone has the rights to ownership.'
'There is no ownership because it comes out of science, rather than from some cardiologist's head,' says Jennie Brand-Miller, in a pop against Atkins. 'We were the first to write a GI book for the public in 1995, to describe the science behind it in a plain English format for the benefit of diabetics ... I don't think any of us thought of it as relevant to weight loss at the time.' And neither did Jenkins in 1981. 'We saw cardiovascular disease as a potentially important application,' he says. 'Its use in body weight control was not our original focus.'
Was this, perhaps, a missed opportunity to develop a global brand? Dr Brand-Miller, who is heralded by her British publisher Hodder Mobius as 'the creator of the GI Diet', concedes that mistakes were made. 'One of the things we did wrong - and I blame my American publisher for this - was that the title that sold so well in Australia [The GI Factor] was changed to The Glucose Revolution for the US market, on the grounds that 'GI' had to do with GI Joe, or gastrointestinal there. So later, Rick had the perfect opportunity to come out with the GI diet. He rode this wave of recognition ...'
Ah yes, Rick. Rick Gallop, Canadian author of The GI Diet and former president of the Heart and Stroke Foundation of Ontario, is rarely off the UK best seller lists these days. He is, so far as the British public are aware, Mr GI himself. But Brand-Miller's not bitter. 'I am a scientist first,' she says. 'My objective is to see the science trickle down to the person on the street. I'd never consider ownership of it. In fact Gallop just dumbed down the message. We aimed for a more educated audience - for dieticians and uninitiated health professionals. David Jenkins and [his associate] Tom Wolever didn't do a good job of explaining it to people from the outset. They are both so involved in the science that they didn't know how to translate it for ordinary people. Rick has done well by aiming at a lower level.'
'The GI idea has been around for years,' admits Gallop. 'So it was a question of packaging , making it - pardon the pun - digestible. If anything, I am the accidental author, I don't lay claim to some great strategy. The timing was fortuitous, there's nothing more sophisticated to it than that.'
Gallop certainly benefited from a series of developments that took the GI to its UK tipping point in 2004. Last August, for instance, US research published in The Lancet showed that the GI diet led to weight loss, reduced body fat and reduced risk factors for diabetes and heart disease in rats.
Meanwhile, the 'death' of Atkins - man and method - had left us receptive to the next big thing. As Gallop says, 'There has been more noise about [GI] in the last few months because people are suddenly looking for an alternative to the most successful diet of the last few years. Atkins left them feeling deprived, bored, limited, hungry and frustrated ...' And, lest we forget, fat all over again once we so much as looked at a muffin.
But our relationship with carbs had altered in those Atkins years. They suddenly became critical to any discussion of diet, though they had barely been mentioned during the low-fat decades. We were ready, spurred on by an increasing awareness of the twin modern plagues of diabetes and obesity, to contemplate the concept of the Glycaemic Index - thanks as much to psychology as science. And once those early adopters had started on the road to GI, there was no stopping its momentum. Modern diets are more contagious than measles.
One of the glories of dieting, and one of the ways diet fads are disseminated so quickly once they've worked up a bit of steam, is that we're endlessly fascinated by talking about what we can and can't, do and don't eat. I know for a fact that 12 people are on GI because of me, and that's not even counting you lot. If we're not banging on about food intolerances and wheat allergies, we're fixated by Courtney Love's weight gain, Sadie Frost's new figure, Kate Winslet's dietary tips. We're glued to Rick Stein, John Burton Race, Ramsay and Oliver on the box, gripped by Gillian McKeith's nannying mock-shock ('Would you look at all these Scotch eggs you're eating in a week! Och, I bet you have aaaawful flatulence!')
Our endless fascination has bred a certain understanding of the basics of sound nutrition and sensible eating. We all know deep down how to lose weight (eat less ... exercise more ... drink water ... yawn) but still we're on a constant lookout for the secret formula that will see off our wretched love handles. Diet addicts - nearly 13 million of us - like being told what to do. It gives us something to blame if it all goes belly up (or out). But why do we so need the crutch of a regime?
According to Dr Andrew Hill, senior lecturer in behavioural sciences at Leeds University, it is the very abundance of food that has turned us into a nation of serial dieters. 'The problem is how to negotiate the huge choice now available ,' he contends. 'It is only in the last micro-second of human evolution that we have become surrounded by a sea of calories. We've become international, non-seasonal feeders and for an increasing proportion of people, this represents a challenge. We simply don't have the psychological controls to cope.
Our biological system is tilted in favour of over-consumption, and telling a hungry person to eat "less" is pointless. How on earth should we restructure and limit what we eat? Why not latch onto a diet, which is essentially a form of coded behaviour? It is easier than going it alone.'
Brand-Miller, too, recognises the importance of dieting psychology. 'If you start talking about high and low blood sugar levels, a lot of people, particularly women tune in. They know what it feels like, you've pressed the right buttons.' It also explains why Gallop's jolly traffic-light system of designating which foods are low, medium or high GI, is proving such a hit over here.
Here's Barbara Amiel Black, wife of beleaguered media baron Conrad Black, with a small homage: 'I'm a binge eater, chocoholic, sit at my desk day and night, can't be bothered to weigh foods or count calories, but help, I am vain! Rick Gallop has been my diet coach for years ... That chart will be taped to my forearm in restaurants - and on the fridge. This is my diet book forever.'
Packaging, marketing, spin - all played a part in Britain's burgeoning GI revolution. And so too did Ruben Renton, aged one. 'Tesco put me in charge of diet and health when son number two had just been born,' explains Hamish Renton, the man credited with introducing GI living to kitchens across the nation. 'I was doing my fair share of night-time nappy changing and so on, and I noticed I was exhausted in the afternoons, and the pounds were creeping on. I tried Atkins, but it didn't feel right excluding carbs. I came across GI studies and thought that it could have some mileage. To find out about GI, though, you have to go to Australia.'
Nine months later, following a team trip to Sydney, Tesco swung its behemothic weight behind the littleknown concept of GI. Today, the company undertakes GI testing at labs in Oxford, Reading and Melbourne. It has GI-labelled 250 of its key products so there's no complicated counting. No peering at the small print on a yoghurt pot - just a bold circle indicating whether your pitta pouches pass muster.
Since 8p in every British pound is spent in its aisles, Tesco's reach to the masses is phenomenal, more effective perhaps than anything the States could dream up to alter UK eating habits. As Renton says, 'We didn't want to overcomplicate things. It's a populist point really: a mum in Barnsley only needs to know that granary bread is low, white bread is high - if she wants to cut out some snacking, go for the granary.'
It seems that Barnsley mums are listening; 65,000 copies of Tesco's GI Guide have been sold since it was introduced in January ('We were gobsmacked by the rapidity of the sale; it indicated a huge untapped demand,' says Renton. 'The books are now changing hands on eBay'). The future may well see the development of foods bioengineered to modulate blood sugar levels, transforming traditionally high-glycaemic foods into low-glycaemic, healthier options. Tesco is currently sponsoring research and development into an understanding of what lowers the GI of a given food - 'the holy grail' whispers Renton.
Certainly, GI has the whiff of longevity about it. Sir Steven Redgrave, a diabetic, was an early convert. Anthony Worrall Thompson, himself a GI proselyte following his diagnosis with Syndrome X, a precursor to diabetes, sums it up: 'I see it as a lifestyle change rather than a diet with a big D. I expect I'll be on it for life.'
In typical evangelical form, Worrall Thompson publishes his glossy GI recipe book this month. 'Before GI, I was always tired by 4pm,' he says, 'and I just thought I was ageing. Now I start the day with porridge, I eat lots of whole-grains and nuts and I've lost two stone and my insulin problems are under control.' Indeed, it is hard to find an expert in nutrition who is not a fan of GI. Since it recommends a balanced diet including all food groups, the flour and potato lobbyists who became so aerated about Atkins have remained unruffled.
Of course, cautious commentators sling the usual 'not proven till it's proven' arrow, forgetting that the science has been around for a quarter of a century. Besides, a study of more than 90,000 women published late last year in the American Journal of Clinical Nutrition showed that women consuming a high GI diet had a 60 per cent greater risk of developing type 2 diabetes than those who had lower GI dietary intakes.
Persuasive stuff, but what criticism there is centres less on the diet's effect than on its methodology. Dissenters point out that the Glycaemic Index of a whole meal will bear very little relation to that of its constituent parts, since it is near impossible to ascertain the influence of additives, fats, previous meals, metabolic rate, whatever, on the performance of a single food. In response, the notion of Glycaemic Load has been developed, to assess the effect of 'real food intake' by multiplying the amount of carbohydrate consumed in grams by its GI score. Not simple, but probably nearer the mark if you're interested in accuracy.
The antagonists, such as they are, also dwell upon a handful of discrepant foods which appear to skew the logic of the diet and can put the unwary consumer off -track. One of these is watermelon - way off limits for a GI dieter, despite its apparent inoffensiveness. (Brand-Miller explains the anomaly: 'A very dilute solution of sugar - as you would find in watermelon - is delivered from the stomach to the small intestine with great rapidity. Therefore it has a high GI.') Peanut butter is another - curiously, it's a low-GI food. Similarly, whole milk is lower than skimmed, fruitcake lower than melba toast - because fat, like fibre, acts as a brake in the digestive process; it also signals the brain that you are satisfied and do not need more food.
The crux of the GI diet, it turns out, is that a low GI alone is not enough; a food must also be low in calories and low in saturated fats. 'Only then,' says Gallop, 'would it pass the test.' The idea is to look out for the right carbs (slow-burners) and the right fats (no hydrogenated oils ). It's also worth humming Gallop's mantras to yourself while you're sitting at traffic lights:
Never use sugar, always a substitute. Eat the fruit rather than drink its juice. Never puree, never mash. Eat raw. Avoid cheese and caffeine. Pasta is a side dish not a meal. Eat every three hours to avoid low blood sugar. Include protein in all meals. A rice cake is diet death. Cover half your plate with vegetables, then a quarter with carbs and a quarter with protein. Cook everything al dente, leaving your stomach to do the extra work ... Once the pounds begin to shift, you'll have no trouble remembering the GI drill. After all, weight loss does breed a certain mild satisfaction. Hell, it breeds a massive high, makes you want to whoop down the street, run naked through town and end up at a shop selling very small jeans. I know it's a bit pathetic. But, come on. Aren't we all?
· The GI Diet, by Rick Gallop (£10.99, Virgin)
· The GI Guide, by Rick Gallop and Hamish Renton (£3.99, Virgin)
· The New Glucose Revolution, by Jennie Brand-Miller (£8.99, Hodder Mobius)
· Antony Worrall Thompson's GI Diet, by Antony Worrall Thompson (£12.99, Kyle Cathie)