Are diet drinks a smart swap?

02:15, Mar 04 2014
Diet coke
YES WE CAN: Health professionals are divided on artificially-sweetened drinks.

The message about too much sugar is starting to resonate in Kiwi homes and is reflected in the rise of "diet" or "zero sugar" fizzy drinks on supermarket shelves.

With so much noise about the danger of sugary drinks and their impact on this country's obesity crisis, it's no surprise to see a rise in sales of artificially-sweetened drinks.

But are diet drinks a valid alternative?

Health professionals are divided - yes, it's good to reduce sugar but there is still huge concern about the effect on our teeth from these highly acidic drinks. And food activists claim the artificial sweetener aspartame, the go-to sugar replacement, is to blame for everything from vaginal irritation and infertility to headaches and multiple sclerosis.


Dr Rob Beaglehole, principal dental officer for Nelson Marlborough District Health Board, refers to obesity as a "preventable crisis".


Eliminating sugar from fizzy drink would make a "huge impact", he says, as the bulk of risk is removed with sugar. However, from a dental perspective, diet drinks are no healthy alternative.

"[Diet drinks] may be free of calories but not of consequences, especially to the teeth."

Diet drinks still have low pH levels, meaning they are acidic. Water, as a neutral solution, has a pH about 7.

"Coca Cola for example, has a pH of 2.3. A diet coke has a pH of 3," Beaglehole says.

"Acid can cause tooth decay and enamel [the substance that covers a tooth] erosion. Diet drinks, even though they don't have sugar, still wear away teeth. I've seen such cases where they have been worn away to the nerves, and you just have to take them out."

"As dentists, we recommend drinking water or unflavoured milk. For treats, fruit juice diluted at least 50 per cent. The main issue with all fizzy drinks is that they displace healthy options."

Also of concern is the still sugary taste of diet drinks, which Beaglehole describes as "maintaining a taste for sweetness, which can lead to poor diet choices".

Murray Thomson, professor of dental epidemiology and public health at the University Otago, agrees with Beaglehole, describing diet drinks as "the lesser of two evils".

"If we have them regularly, the acid in them erodes the teeth and also makes them more susceptible to wear when we chew," Thomson says. "Soft drinks are best kept as a treat for special occasions, not as daily or twice-daily alternatives to water."

In an ideal world, children would not drink soft drinks at all on a regular basis, he said.

But sometimes the lesser of two evils is the preferred choice, says Boyd Swinburn, professor of Population Nutrition and Global Health at the University of Auckland.

"There's a gap between what's ideal and what's achievable," he says. The lesser evil may, at this stage, be the realistic option.

He worries for the third of New Zealand children who will make the transition from healthy to overweight before they become adults. Not to mention the third who are already overweight, and who will remain that way.

"In the first instance, shifting from sugary drinks to diet versions is not as good as water, but it's a step in the right direction. By removing the sugar, that gets rid of the obesity related problem. However, the issue of high acidity and dental erosion still remains," he says.


When I was working, one university holiday, at a tasting demonstration, few people were keen to try anything with "artificial" sweeteners. Why? Because it's unnatural, they said, as they loaded their trollies with sugary drinks.

Recently, attitudes have started to change. Sugar sweetened drinks are in long term decline, Coca Cola Oceania general manager Paul Fitzgerald says.

Low calorie brands now account for 25 per cent of the company's range. One in three soft drinks purchased today in New Zealand are sugar-free.

Fitzgerald says as part of Coca Cola's 2013 public commitment to fighting obesity, it's offering more "no" and "low" calorie beverage options, to reflect that "Kiwis are making different choices to suit their lifestyles".

The company develops a variety of low and no-calorie drinks using a variety of non-nutritive sweeteners, including stevia, aspartame and others, either individually or in combination.

Within the wider food industry, aspartame is the preferred sugar alternative, because its intense sweetness (200 times that of sugar) goes a long way and it doesn't alter the product's taste profile (unlike the "natural", plant- derived sweetener, stevia).

However, anti-aspartame activists are widespread and outspoken. A quick Google search for "aspartame" reveals alarming results.

In 2007, a food safety expert received death threats over her assurances that aspartame was safe. Sandra Daly, the deputy chief executive of the New Zealand Food Safety Authority (NZFSA), was accused of "poisoning" New Zealanders in messages on internet blog sites. One blogger posted: "Someone please kill the bitch."

Conflicting opinions bombard the public, unnecessarily tainting aspartame's reputation.

Ian Shaw, a professor of toxicology and author of Food Safety , doesn't like the idea of using synthetic additives of any sort but aspartame is an exception, he says. It's safe.

"This is very unusual for me to say this, but no, most people should not be worried about ingesting aspartame. Toxicologists look at additives to assess risk they pose to human health. For aspartame, the risk is very low for most people."

A small number of people have a rare inherited disorder called phenylketonuria (PKU). These people are unable to break down phenylalanine - a component of aspartame, leading to harmful levels of it in the blood stream. Usually people with PKU are diagnosed shortly after birth, with a blood prick, and will be following a strict diet to avoid phenylalanine.

"[PKU sufferers] are absolutely aware of who they are," says Shaw. "The requirement is that [aspartame] is indeed labelled, so these people can easily avoid it."

Shaw says aspartame has gained a reputation for what it is - a synthetic additive - rather than for what it does.

"The companies that are using it have been through very very extensive toxicity testing. Simply because it's so widely used. You would see the side effects very quickly in the population. The companies would be in court. They would lose their livelihoods. They are clearly being extremely careful. Which is good, that's how it should be."

But what about, as one advocacy group says online, the "poisons" that aspartame releases into the human body upon digestion?

Simply not true, Shaw says. In fact, many fruits break down into the same chemicals, and contain much higher levels of them.

"An awful lot of natural compounds are an awful lot worse than man made ones. The chemistry of the natural ones can someone have the same chemistry of man made ones. One of the big problems is that the public are getting a whole load of views from different places. And there's a little boring scientist or regulator sitting in the corner whispering, this is OK. And then there are 27 activists yelling and screaming, and people are much more likely to hear the activists than the scientist."

Such paranoia does have a positive side, he says, in that it keeps the companies and regulators on their toes. That is a good thing.

But it can distract from the larger problem - in every sense of the word - which is perhaps a bit closer to home.


New Zealanders, on average, consume about 54kg of sugar per person per year. That is equivalent to 37 teaspoons of sugar per person per day. The World Health Organisation recommends an average adult has 12 teaspoons of sugar per day.


First discovered in 1965, Aspartame is a sweetener used to replace sugar in a range of food and drinks. Aspartame has been blamed for range of negative health effects, around cancer, neurological effects, and allergic reactions. More than 90 countries worldwide, including New Zealand, have independently reviewed aspartame and found it safe for humans.

Aspartame cannot be used in baking or cooking because it is unstable when heated. It also breaks down in liquids during prolonged storage, and artificially sweetened products are labelled to reflect this.

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