by Nicola Garrett

It’s hard to know what to believe when it comes to sugar. Some say it’s toxic and directly responsible for a range of chronic diseases; others say it’s simply another form of over-consumed kilojoules. We’ve asked one of the world’s leading researchers on the topic to take us through the latest evidence.

When it comes to sugar there are a few points on which most experts agree. Much of the sugar we consume is hidden in foods most of us eat every day. Too much sugar is bad for your teeth. We need to limit how much added sugar we consume in our diet, especially sugary drinks.

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Beyond these points, it can be hard to know what to believe in the sugar debate.

Sucrose, which is made up of fructose and glucose, is the most common form of added sugar used in Australia. We’ve long been told refined sugars like, sucrose, are nothing more than empty kilojoules and aside from being bad for your teeth and contributing to extra centimetres on your waist, they’re unlikely to affect your health.

But a growing body of research links sugar consumption to significant health issues including obesity, type 2 diabetes and heart disease. This has lead to anti-sugar campaigners, such as US endocrinologist Professor Robert Lustig, to call for sugar to be regulated and taxed, much like alcohol or tobacco.

Teasing apart the hard science from the hype on this topic is difficult, so we've asked Professor Jim Mann, who's spent decades studying the impact of sugars on our health, to take us through the research.

Sugar is making us fat

Obesity rates in Australia are climbing faster than anywhere else in the world; a recent study in The Lancet revealed 63 per cent of us are overweight. This is a concern as obesity is a major risk factor for type 2 diabetes, cardiovascular disease and some cancers.

But how much can we blame sugar for our expanding waistlines?

Mann, a professor in the Department of Human Nutrition and Medicine at University of Otago in New Zealand, and his colleagues have reviewed the evidence for the revision of the WHO guidelines. They found 68 studies that directly looked at the effects of free sugars – those added to foods or naturally occurring – on body weight.

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Their analysis showed that reducing the amount of free sugars in the diet had a small but significant effect on body weight in adults – an average reduction of 0.8 kilograms.

Interestingly, they found that an increase in sugar intake was associated with a corresponding 0.75 kg increase in body weight. This parallel effect, the authors suggested, was due to changes in the amount of energy (kilojoules) consumed, since replacing sugars with other carbohydrates did not result in any change in body weight.

Mann argues sugar contributes to obesity because it is high in kilojoules and you can consume a lot of it without even realizing it, especially if you're consuming it in the form of sweetened drinks.

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"If [sugar] is taken in liquid form it seems that the body or the brain is incapable of detecting those calories and converting that into a feeling of satiety. Whereas if you have sugar or any other calories in solid form it seems that the body says 'right I've just had some calories and sugar'".

"If we have a diet that has a lot of sugar then you are going to gain weight because it's just so easy to have those calories."

However there are those that believe the adverse effects of sugar go beyond the kilojoules and the inevitable weight gain.

Lustig refers to sugar as a toxic 'poison', and believes it is solely responsible for a number of chronic diseases, including heart disease, cancer and type 2 diabetes.

His theory is that excessive amounts of sugar drive up insulin secretion that triggers the body to use the sugar either as fuel or to store as fat. As well, insulin blocks the hormone leptin, which sends signals to the brain to tell us when we've had enough to eat, which essentially means that if we don't have enough of it we'll just keep on eating.

This is why Lustig wants sugar to be regulated like tobacco and alcohol, but many consider his views to be extreme, or at the very least, overstated.

Yet there is some evidence sugar has an effect beyond calories and weight gain. In particular, fructose can be particularly detrimental, says Mann. In their recent review of studies, Mann and his colleagues found sugar had a negative effect on blood pressure and cholesterol, which was independent of any weight gain.

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"It does seem that sugar has a small effect on BP and lipids, it may mean that in susceptible individuals it has a bigger effect but overall there is definitely an effect".

Despite this, Mann doesn't describe sugar as a toxic substance.

"There probably is more to sugar than just calories but maybe Lustig has overstated the cause," he says.

And the big question is that if there is an effect of sugar beyond calories we don't actually know how important the effect of that is globally, he says.

"How big a contribution does the non-calorie component of sugar contribute to the epidemic of ill health that we have?"

What about type 2 diabetes?

Most experts say any link between sugar and type 2 diabetes is indirect and more to do with the weight gain that comes from the extra kilojoules many of us consume as sugar. Being overweight is a known risk factor for type 2 diabetes.

But in recent years there's been some evidence suggesting sugary drinks can increase your diabetes risk.

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"There is data that suggests that sugar increases the risk of diabetes, but how big that risk is remains to be seen," Mann says.

In a study of more than 90,000 women, those who had one or more sugar-sweetened soft drinks a day were twice as likely to have developed type 2 diabetes during the study compared with those who did not consume sweetened drinks. But many of these women had also gained weight.

However, researchers from the Stanford School of Medicine in the US examined data on sugar and diabetes rates from 175 countries and found a link between sugar and diabetes that was independent of obesity rates.

For every additional 150 calories of sugar per person per day, the prevalence of diabetes in the population rose by 1 per cent, even after taking into account obesity, physical activity, and other types of calories.

While the findings do not prove that sugar causes diabetes the researchers say that the findings provide support for studies that have suggested that sugar affects the liver and pancreas in ways that other types of food or obesity do not.

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Is sugar directly linked to heart disease?

As well as evidence showing that sugar directly increases blood pressure and cholesterol, both known risk factors for heart disease, research suggests there could be a more direct link between added sugars and heart disease.

A recent US paper, based on a study that followed a large number of adults for over 14 years, found that consuming added sugars significantly increased the risk of death from heart disease. Over the course of the study, participants who consumed 25 per cent or more of their daily calories as sugar were more than twice as likely to die from heart disease as those whose diets included less than 10 per cent added sugar.

Other research showed that women with diets that had a high glycemic load (increased blood glucose associated with sugar intake) had an increased risk of coronary heart disease, with those in the highest bracket of consumption having a more than two-fold increased risk over 10 years of follow-up.

And a study that followed 40,000 men for two decades found that those who had one can of sugary drink per day had a 20 per cent higher risk of having a heart attack or dying from a heart attack than men who rarely consumed sugary drinks.

But these studies alone aren't enough to prove that sugar causes heart disease, as it's not clear that the link is directly attributable to sugar and not another confounding factor.

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In a scientific statement on cardiovascular disease and sugar the American Heart Association suggests: "No data suggest that sugar intake per se is advantageous, and some data suggest it may be detrimental. Taken in total [the studies] indicate that high sugar intake should be avoided. Sugar has no nutritional value other than to provide calories."

Sugar and cancer

While some cancers have been linked to sugar it is hard to say just exactly what the link is, says Mann.

"When it comes to causes of cancer sugar may be very relevant but the link is likely to be indirect ... Sugar contributes to obesity and of course obesity is a major risk factor for a number of very important cancers like postmenopausal cancers, and colorectal cancers," he says.

The bottom line

So after going through all the research, Mann's view is that we should all adopt the WHO guidelines and reduce the amount of sugars we consume in our diet to no more than 10 per cent of our total energy.

"We're not going to be able to cut out sugar entirely, that's impossible and nor should you. But people should get most of their sugar from natural sources, and by natural I don't mean honey, or cane sugar, I mean sugar that occurs naturally in fruit and vegetables.

"I buy into these WHO guidelines because I was part of developing them. Definitely reduce to 10 per cent or less."

This article originally appeared on the ABC and has been republished with permission

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