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Monday’s medical myth: sugar is the main culprit in obesity

Sugar doesn’t play a greater or lesser role in obesity than fat and other carbohydrates. Esther Gibbons

The debate about the health implications of sugar consumption began back in 1972 when Professor John Judkin, from the University of London, published Pure, White and Deadly, which linked sugar intake to heart disease and type 2 diabetes.

While more recent studies – such as the long-running Nurses’ Health Study – have found no such link, there are other important factors at play in the sugar debate.

Since the 1970s, we’ve seen a vast increase in the consumption of sugar-laden soft drinks and a dramatic rise in obesity. Children and adolescents are getting a greater proportion of their energy intake (up to 25%) from sugars, especially from soft drinks.

In Judkin’s day, sugars in biscuits, cakes, desserts and other sweet treats came with some nutrients, vitamins, minerals or fibre. Soft drinks have no such redeeming features.

Overall, the increase in sugar from soft drinks has been accompanied by a decrease in sugar in other forms, so total sugar consumption has not increased.

Not all sugar is equal

Sugar is a sweet, simple carbohydrate that takes three natural forms:

  • Fructose is found in fruits and vegetables such as apples, pears and onions.

  • Sucrose is derived from cane and beet sugar. It’s known as a disaccharide (a molecule of glucose and fructose bonded together).

  • Glucose is the sugar our bodies use to power the brain, heart and muscles. The body needs to tightly regulate its glucose because excessive levels in the blood (diabetes) can damage cells.

Sugar and obesity

So has sugar played a larger role than fat, protein and other forms of carbohydrates in Australia’s obesity epidemic?

Probably not. There has been little change in the proportions of fat, carbohydrate and protein in our diet over the past 30 years. But total energy intake has increased – we’re gaining weight because we’re eating more of everything.

Overall, it seems that total sugar intake hasn’t played an undue role in the increase in obesity.

Domestic sugar consumption fell from 55kg per head in 1976 to 50kg per head in 1984 and it seems to have remained stable ever since (though data is only available to 1996). Sugar production hasn’t increased since 1996 and sugar-product imports are negligible, accounting for just 5% of confectionery and bakery goods.

Soft drinks are the exception and now account for a fifth of the average Australian’s sugar intake. Consumption of soft drinks doubled from 47 litres per head in 1969 to 113 litres per head in 1999.

Sugar and heart disease

There’s no doubt that sugar-sweetened beverages are associated with type 2 diabetes. Studies show women who consume more than one soft drink a day have a 40% to 80% increased risk of diabetes and a 28% to 32% greater risk of heart disease.

But sugar isn’t alone in increasing these risks. Eating large quantities of any carbohydrate with a high glycemic index (white bread, for instance) can double the risk of heart disease and diabetes.

Likewise, consuming large amounts of trans fat has been shown to increase the risk of heart disease by 33%. So sugar in soft drinks increases the risk of disease by a similar amount to trans fat and white bread.

Sugar and weight loss

A 2009 study of the effects of high liquid sugar intake found those who consumed a quarter of their daily energy intake as liquid sugar - either glucose or fructose – were more likely to have a greater appetite and gained around 3kg over the ten-week study period.

They will also notice other metabolic changes, such as increased blood fats and higher insulin levels, which increase their risk of heart disease.

Even when there’s no overall weight gain, excessive consumption of sucrose-based soft drink can raise liver fat. This makes insulin work less effectively, raises blood glucose and can also lead to long-term liver disease.

So will quitting sugar help you lose weight?

Swapping soft drinks for water or even diet drinks will undoubtedly help you lose weight. And cutting out other sugar-containing foods and drinks will help you reduce your total calorie intake because of the associated reduction in starch and fat intake. This will lead to longer-term weight loss.

But removing “natural” sugars – and therefore eliminating nutrient-rich fruits and milk – is not a sensible solution. Sugar, as a nutrient class, does not contribute any more to obesity than an excess of fat or carbohydrates.

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