The glycemic index (GI) is not just bad science, it has a dangerous loophole big enough to drive an ice-cream truck through. Its time it went to the place where old (and wrong) public health messages go to die.

Wendy’s Chocollo (with waffle cone), Bulla Light vanilla ice-cream, Nestle Milo, Uncle Toby’s Choc Chip Crunchy Muesli Bar and CSR LoGiCane Sugar all have something in common. Yes, they’d all look pretty good on the dessert menu, but they also share something else. The owners of each of these products (and almost 100 others like them) have paid for the right to display a GI symbol.

Much like its more famous cousin (the Heart Foundation tick), the GI symbol is designed to guide confused consumers towards “healthier choices” in the supermarket.

The symbol alerts us to foods that have a low glycemic index. The GI is a measure of the amount that a food affects our blood-sugar levels. Our body converts most of the carbohydrates in our food to blood glucose. This causes a spike and then a decline in the amount of glucose we have in circulation.

But not all foods are equal. Some (such as glucose) spike our blood sugar levels more quickly than others (such as potatoes). This is because the carbohydrates in some foods are more quickly converted to blood sugar than others.

The glycemic index of a food is measured by comparing the way a healthy person’s blood-sugar level responds (over a two-hour period) to 50g of glucose and how they respond to 50g of carbohydrate in the food being tested (let’s say boiled potatoes). If the tested food produces an effect that is 70% of the one measured for the glucose, then it is said to have a GI of 70. A low GI food is one that has a GI of 55 or less (meaning that the blood-sugar response is 55% of that of pure glucose over a two-hour period).

The theory goes that if we could make sure we were eating just the foods that have a low impact on our blood sugar, then we would keep our blood-sugar levels more even (and presumably somehow be more healthy as a result). I say presumably because there is a real scarcity of credible evidence that the GI of a food has any measurable (positive) health impact.

GI may be a pointless academic exercise but it is not a harmless one. It has a hidden danger in that the carbohydrate it assigns the lowest (and therefore the best) rating is fructose (it has a GI of 19). Fructose is a very sweet tasting (almost twice as sweet as sugar) carbohydrate that does not produce a significant blood sugar response.

When this little quirk of fructose was first discovered (in the early 1980s) it was pronounced a miracle sugar for people with diabetes. They could have sweets just like everyone else and their blood sugar would never spike as long as the sweets were made with fructose. Even some sugar was OK too (because, being half fructose, it also has a low(ish) GI).

Diabetes organisations the world over happily advised diabetics they could eat sugar or, even better, pure fructose. Unfortunately for sweet tooths everywhere, by about 2001, it was becoming abundantly clear that the “no free lunch” rule applied (or was it no free pudding?). Fructose was even more dangerous for diabetics than sugar.

It turned out that the reason fructose didn’t have a big glycemic index was because it is converted to fat (by our liver) and not circulating blood sugar (like just about every other carbohydrate). Telling diabetics (or anyone else, but particularly diabetics) to consume a substance that was immediately converted to fat was a very bad idea (verging on the culpably negligent).

The American Diabetes Association quietly withdrew its recommendation in 2002, but the message never got through to Australia. The Australian Diabetes Council tells us it “wants to end the myth that sugar causes diabetes”, apparently because sugar-free diets aren’t “much fun”.

And the folks selling the Low-GI stickers (the GI Foundation — a collaboration of University of Sydney, Diabetes Australia and the Juvenile Diabetes Research Foundation) still tell us it is “best to ignore the sugar content of a food and instead focus on the food’s GI”. A director of the GI Foundation (Sydney University nutritionist Jennie Brand-Miller) even went so far as to say recently that “Unlike saturated fats, trans fats, salt and alcohol, sugar doesn’t actually do any direct harm to the human body”.

For the past decade (at least), the research on fructose (and sugar) has shown again and again that exactly the opposite is true. Fructose consumption is a causal factor in obesity, heart disease, hypertension and type II diabetes. It is implicated strongly in cancer growth and it is highly likely to be behind the explosion in the number of cases of chronic kidney disease and fatty liver disease.

That all sounds pretty harmful to me. So perhaps that is why the American Heart Association recommended (after reviewing all the evidence in 2009) that Americans needed to dramatically reduce their sugar consumption. Men should consume no more than nine teaspoons of sugar a day (about a can of soft drink’s worth). That’s less than half the current (vague) Australian recommendation (of about 23 teaspoons a day).

The glycemic index seemed like a good idea in the eighties. It held out hope (for a dessert-filled future) to millions of diabetics everywhere. But science eventually found out what was really going on (as it usually does) and the world moved on.

In Australia we got stuck on the notion that GI should work (and to this day stubbornly refuse to acknowledge the fructose loophole). The food industry leapt on the marketing power of a “healthy label” that meant it could still use as much sugar as it wanted. Positions became entrenched. Reputations were built. And as a result we now have folks such as the GI Foundation and the Australian Diabetes Council telling us there’s nothing wrong with eating sugar.

This would all be mildly entertaining if we weren’t talking about real people with very real (and very life-threatening) problems. Every day in Australia nine peoplelose a limb to type II diabetes (and 275 more people develop the disease). Every day the number of obese children grows like never before. Every day the number of new cases of chronic kidney disease sets a  benchmark.

The science says all of this misery (and lots more) can be traced to eating sugar. So how about we stop playing ducks and drakes with quaint scientific notions (that protect the processed food industry from having to face reality). How about we start caring about the people who follow the advice they see on a packet of food. How about we face the truth about sugar and demand that those we pay to care — do.