Australasian Science: Australia's authority on science since 1938

Pure, White, But Maybe Not So Deadly

By Tim Olds

Is there something uniquely unhealthy about sugar above and beyond the excess calories?

There are some personal matters one is reticent about putting into print in a national magazine, but here is one: I take three sugars in my tea. I will also confess that breakfast cereal for me is pretty much just a vehicle for cream and sugar. So I’ve been a little alarmed by the recent controversies around sugar and sugar taxes.

Sugars are carbohydrates with a caloric density of about 16 kJ per gram. Table sugar (sucrose) is a combination of glucose and fructose. These sugars have slightly different molecular structures, and are broken down by different pathways in the body. High-fructose corn syrup, which is derived from corn and is widely used in the US, particularly in soft drinks, is also a mix of glucose and fructose but has a slightly different molecular structure to sucrose.

About 20% of calories in the US adult diet come from simple sugars, of which two-thirds is in the form of added sugars (table sugar and sugars added during manufacturing) and the rest from naturally occurring simple sugars (such as in honey and fruit). In the US, about one-third of all added sugars come from sugar-sweetened drinks. The World Health Organization suggests that no more than 10% of total energy intake, and preferably no more than 5%, should come from simple sugars.

It’s notoriously difficult to put together reliable data on trends in diet, but economic and dietary survey data indicate that consumption of added sugars has been falling for the past 15 years in the US and UK, and perhaps Australia.

There are two broad mechanisms proposed as to why sugar might be harmful for health. The most obvious one is that sugar provides excess calories, which in turn leads to obesity and obesity-related diseases. The second is that there is something uniquely bad about sugar above and beyond the excess calories. The consequences of high-sugar diets, it is argued, are worse than the consequences of equally calorie-excessive high-fat diets.

One version of this latter approach argues that the culprit is fructose. The fructose hypothesis is based largely on epidemiological evidence – increases in the use of high-fructose corn syrup mirrored increases in obesity – and studies in rodents and humans using pure fructose.

But the fructose hypothesis has been strongly criticised by the dietary establishment. The UK’s Scientific Advisory Committee on Nutrition in 2015 concluded that “there is insufficient evidence to demonstrate that fructose intake ... leads to adverse health outcomes independent of any effects related to its presence as a component of total and free sugars”. The American Medical Association and the Academy of Nutrition and Dietetics agree.

The epidemiological evidence linking fructose intake to obesity is particularly weak: spurious “ecological” correlations of this sort are very common. For example, over the period 2000–09, cheese consumption in the US was very highly correlated with deaths caused by entanglement in bedsheets. Of more relevance is a decline in fructose consumption since 1999 while obesity rates have continued to increase.

The clinical trial data have also been criticised for using excessive amounts of fructose – sometimes five times greater than the average US consumption and three times greater than the amount of sugar consumed by the top 5% of US consumers. Feeding people only fructose or only glucose also doesn’t mimic the way we actually eat – we almost always consume a mix of fructose and glucose. It’s a bit like feeding someone nothing but bananas for a week, and concluding that bananas are bad for us.

Finally, trials in which normal sugar intake was replaced with fructose without changing the total number of calories reported no effect on weight gain, blood pressure, internal fat or blood sugar or insulin levels. Therefore it seems that eating fructose in typical amounts does not lead to adverse health consequences or increase the risk of heart disease, diabetes or obesity over and above the effects of increased caloric intake.

Yet it has been suggested that it’s easier to over-consume sugar, particularly in liquid form, than other types of food. Sugar may also bypass some of the complex mechanisms that tell us we’ve had enough.

But there’s not a great deal of evidence to support this hypothesis. Sugars trigger satiety in much the same way as other nutrients. While fructose only results in small increases in insulin (a satiety signal), other mechanisms kick in so satiety is much the same as for glucose. Soft drinks suppress appetite to the same extent as the same number of calories consumed as milk or fruit juice.

It’s possible, however, that calories consumed in liquid form suppress appetite less than the same amount of calories consumed in solid form. In particular, thirst may trump hunger, and we may drink calorie-rich beverages to conquer thirst, the excess calories being collateral damage.

All this doesn’t mean that it’s OK to eat as much sugar as you like, or that reducing sugar intake, even through sugar taxes, is not a good strategy for reducing energy intake and obesity-related diseases. (I personally think it’s worth a go, but don’t expect miracles.) It probably does mean, however, that there’s nothing particularly deadly about sugar (or fructose, or soft drinks) per se, and that associations between sugar intake and poor health are probably just a matter of excess calories.

So now I can have a cup of tea, which as I mentioned I take with just one sugar.

Tim Olds leads the Health and Use of Time Group at the Sansom Institute for Health Research, University of South Australia. He has received funding from Coca-Cola Corporation for conference travel and accommodation, the National Health and Medical Research Council, the Australian Research Council, Beyond Blue, SA Health, the Department of Health and Ageing, the Australian Food and Grocery Council, the Financial Markets for Children Fund, and Channel 7.