Like the tasty foodstuffs they frequently declare war on, it seems all diets come with a sell-by date. This month has seen time called on Dr Atkins' low carbohydrate road to svelteness, as the late doctor's heirs in Atkins Nutritional filed for bankruptcy protection in the US, with debts of $300m. There were few mourners among the slimming classes, who are in the process of swapping allegiances again - this time from the GI to the GL diet.
The Atkins influence is not entirely over, however. Its direct successor, the GI diet, uses the glycaemic index, a database created by Australian researchers to measure the speed at which foods are broken down by the body and which underpinned the book Dr Atkins' New Diet Revolution. Foods with a high GI (honey, potatoes, white bread and beer) break down quickly and cause a spike in blood sugar, which in turn causes a spike in blood insulin, which turns the excess blood sugar into fat. The sudden drop in blood sugar leaves the body hungry again, and searching for its next food fix. In something of a triple whammy, insulin also inhibits the conversion of fat back into glucose for the body to burn off as energy, an unwelcome throwback to the needs of our hunter-gatherer ancestors to be able to store fat over the lean seasons.
Dieters who stick to low GI foods (those that score less than 55) produce less insulin. Among the ranks of the virtuous are some of the usual suspects - green vegetables and lentils - but there are some gratifyingly unusual ones too. Dark chocolate gets a score of 22 because its high fat content slows digestion, and for this reason nuts and avocados are also popular.
Some nutritionists have worried that such endorsements may lead dieters to feel they have a green light to tuck into these highly calorific foods with abandon. Their fears might not be groundless, GI dieters are credited with a 600 per cent rise in the sales of Brazil nuts in the UK.
GI does come with many of the trappings of a fad diet - surprising superfoods, celebrity adherents such as the Clintons and Sex and the City's Kim Cattrall - but it is actually more of a long-term healthy eating plan. The World Health Organisation has endorsed low-GI eating and the reasonably conservative British Dietetic Association, which declared itself "very pleased to see the back of the Atkins diet", says low-GI foods can help weight-loss by regulating appetite.
"Slow steady rises and falls in glucose may help you feel full for longer," says a BDA spokesman. "But it isn't a magic bullet for weight loss." The adage that the only guaranteed way to lose weight is to burn more calories than you're putting into your body still holds.
Although there is nothing to rival the controversial theories of Dr Atkins (the infamous bad breath associated with his diet was a result of his obsession with inducing ketosis, a physiological state where the body starts rapidly to cannibalise its fat stores), GI has thrown up a few anomalies. Certain fruits and vegetables, for instance, clock up high GIs, most notably fresh watermelon gets a higher GI score than ice cream. So enter the glycaemic load (GL), it is the same but better.
GL is the result of GI's maths being redone by the Department of Nutrition at Harvard Medical School. Essentially it has recalculated the scores according to the portion sizes people actually eat. GI ratings are based on a flat score of how 50g of fast carbs in that food will affect your blood sugar. Foods with a score of 10 or under are classified as low GL, 11-19 as medium GL, and anything 20-plus as high.
"There's no doubt the carb content does affect insulin and the GI is valid," says Dr Fedon Lindberg, author of GL book The Greek Doctor's Diet. "But the current scores are not a true reflection of the food's potential to cause harm or make good. These GI figures don't take into account portion sizes."
So carrots have a GI of 58, up there with white bread. But you would need to eat a portion of about 700g for them to affect you in this way; a typical serving of 100g would give them a GL score of 4. Similarly, watermelon's GI of 72 is based on the 50g of fast carbs contained in a whole fruit. Working on the assumption that even the most fervent melonophile is more likely to restrict themselves to a couple of slices, the GL comes down to 4.
It is not all more food, less flab on the GL diet. Many types of pasta and rice, which have low to medium GI scores, clock up high GL scores. In many cases you would be better off with potatoes (small new ones get the thumbs up from some GL dieticians, chips and packet mash potatoes get the thumbs down).
Ultimately, both GL and GI are flawed because they measure food as an isolated element in a laboratory, rather than as a component of a real-life meal. "There's no such thing as the GI of a potato," says Dr Marc Hellerstein, a professor of nutrition at California's Berkeley college. "It depends what you are eating with it."
GL could work as an exact science if all our meals consisted of a single food but we slap butter on our toast, put Parmesan on our pasta, and eat our chicken with vegetables roasted in olive oil. Then we wash it down with a glass of orange juice. And so each meal has its own unique GL, impossible to measure accurately because our combinations of foods are potentially infinite.
At the moment using GL as a guide to healthy eating seems a good strategy. But in the 20 years prior to Atkins' fall from grace we have seen low calorie diets trashed by doctors claiming the body just becomes more efficient at squeezing fat out of the calories you put in, and low-fat diets discredited as food manufacturers merely replace natural fats with calorific sugars. Who is to say low-GL will not go the same way, with a new slimming panacea waiting in the wings to replace it? My personal favourite at the moment is the Jesus Diet, the work of Florida doctor Don Colbert, who has prescribed the New Testament's staples of fish, fresh fruit and vegetables, and red wine to solve America's obesity crisis.
Gimmicky? Let he who is without love-handles cast the first stone.
HOW THE ATKINS DIET FELL FROM GRACE
Like many humbled empires, Atkins has been brought down by some of the factors that made it successful in the first place. Regardless of the veracity of the science behind them, most diets work initially because they set limits to what you can eat. Atkins’ attack on carbs cut out easy snacking (unhealthy crisps to seemingly more healthy fruit smoothies), and replaced it with less convenient alternatives - it is one thing to throw a bagel into your briefcase on the way to work, another to do the same thing with a fried egg or rashers of bacon.
The net result is that in the short term dieters eat fewer calories. But in the long term? Everyone knows an Atkins dieter who has “put it all on again”. “Low-carb diets are hard and perhaps people found they did not work in the long term,” says Lynn Dornblaser of market analysts Mintel. “Certainly Americans found it hard to maintain eliminating whole categories of food.”
There are other theories behind Atkins’ fall from grace. In his intriguing memoirs ‘The Hungry Years’, food addict-turned-Atkins enthusiast William Leith posits the idea that to champion a low-carb diet is to bring the wrath of the food industry down on your head. Advocate, say, a low-fat diet and producers can easily recalibrate - what they lose on cream they will make up on skimmed milk. “But millers and potato farmers work in high-bulk, low-margin industries. If their sales drop by just a few per cent they have to lay off thousands of workers,” writes Leith. “Low-carb, in other words, potentially harms the food industry in a way that low-fat does not.” And the knock-ons can be dramatic, in 2004 the Federation of Bakers estimated sliced loaf sales had dropped by 200,000 tonnes since 2002. MS
Mike Shallcross is associate editor of Men's Health magazine.
