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The sweet truth about diet soda

A certain sugary carbonated cola beverage was introduced to the world as a tonic in the late 19th century. Fast-forward nearly 100 years: as waistlines began to expand at a rapid rate, people became more and more concerned with watching their weight. Enter diet soda. 

By Eulogi Rheeder

In the ’80s a new sweetener, called aspartame, became a key ingredient in a sugar-free diet version of the drink and was deemed safer than previous options. Today, aspartame is the go-to sweetener in all major diet drinks. However – much like its older sister saccharin – it has been the subject of many studies and much controversy, particularly around its role in the rise of cancer, depression and weight issues over the past 35 years.


The list of medical conditions linked to aspartame is pretty extensive: multiple sclerosis, lupus, seizures, depression and anxiety, migraines and birth defects. Most hair-raising is the chemical’s alleged role in causing cancer. One study in particular (conducted in 2005 by Italy’s European Ramazzini Foundation) found a high dose of aspartame may increase the risk of blood-related cancers – leukaemia and lymphoma – in rats.

Irene Labuschagne, dietitian at the Nutrition Information Centre at Stellenbosch University, has done extensive research on aspartame. She says more evidence is needed to prove that aspartame is, in fact, dangerous. ‘There are many reports floating around, but most of the articles are based on unsubstantiated research or anecdotal evidence,’ she explains. ‘For starters, the study that was conducted in Italy has since been proven inconclusive, as it lacked some important data to substantiate the claims – I’ve seen it and have to agree with the authorities who invalidated the findings.’

Irene explains that the US Food and Drug Administration (FDA) and the European Food Safety Authority (EFSA) – both of which are made up of trained medical, science and nutrition experts – have done extensive research into the substance and have not been able to find a conclusive link between aspartame and cancer.

Furthermore, the National Cancer Institute in the US ran a study in which cancer rates in more than 500 000 older adults were closely studied. The study found no increased risk of lymphoma, leukaemia or brain tumours in those who consumed drinks containing aspartame, compared to those who didn’t.


The scary rumours of cancer and tumours may have been largely disproved, but the sweetener has recently also been linked to depression. A 2013 study conducted by the US National Institutes of Health (NIH) surveyed 260 000 older adults and found that those individuals who drank four or more cups of diet soda sweetened with aspartame a day were 31% more likely to be diagnosed with depression over a 10-year period.

‘This is a tough one to answer,’ admits Irene. ‘I have seen and studied reports that prove a large daily dose (about 600 mg) of aspartame has no effect on the psychological and physiological functions of the brain, nor does it have an effect on the behavioural functioning in healthy adults. But one study did find that a small number of depressed patients experienced a worsening in depression when they consumed aspartame.’

However, Irene points out, the results of this study have not been confirmed, so she cannot conclude whether or not it is fact. ‘Still, individuals who suffer from depression should consult their doctors before introducing aspartame into their diets or altering their current level of intake.’


While science has proven, and continues to prove, the safety of aspartame in diet cooldrinks and all other food and drinks, Irene does give a stern warning against its consumption for people with phenylketonuria (PKU).

‘PKU is a rare hereditary metabolic disorder. Individuals suffering from it have elevated blood levels of phenylalanine because their bodies lack the sufficient enzymes to metabolise it. Aspartame is a huge source of phenylalanine and can be dangerous to people with this condition,’ she explains.

Irene is also very adamant that neither she nor any of her colleagues promote drinking diet cooldrinks. ‘In fact, I do not endorse any kind of soda consumption. It often replaces the nutritional value of certain items such as tea and coffee – these contain antioxidants that are highly beneficial for your body,’ she explains.

In addition, aspartame provides your body with only four calories per gram in energy, but because of the intense sweetness – it is 200 times sweeter than sugar – the amount of essential energy that you actually consume is negligible.‘Aspartame is only useful if it is paired with a well-balanced diet – not a pizza or burger and certainly not a meal devoid of any fresh vegetables, fruit or good protein.’

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