The debate rages on, with conflicting studies and opinions.

In December, the European Union's food safety watchdog, the European Food Safety Authority (EFSA), released a risk assessment report saying that aspartame and its breakdown products poses no health risks at approved consumption levels.

The report concluded that the no-calorie sweetener could be used by pregnant women and that it does not cause cancer, harm the brain or nervous system, or affect behaviour or cognitive function.

The acceptable daily intake is set by the EFSA at 40 milligrams per kilogram of body weight per day. That is equivalent to 2,400mg for a person who weighs 60kg. The US Food and Drug Administration has set the limit at 50mg/kg.

A can of diet soda usually contains about 180 milligrams of aspartame, according to the American Cancer Society, so a typical adult would have to drink more than 13 cans to exceed the recommended limit.

A University of Adelaide study has since revealed that drinks sweetened by Ace K and sucralose had the same effect on a healthy human gut as a glass of water.

The finding, published in the journal, was contrary to other studies that showed artificial sweeteners have a negative impact on the body, including the storage of fat.

The study also questioned whether these sweeteners had any benefit, such as producing responses that signal fullness to the brain.

"So far it appears that artificial sweeteners have limited impact in the short term, but in people in a pre-diabetic or diabetic state, who are more likely to be regularly high users of artificial sweeteners, it might be a different story altogether," says study co-author Dr Richard Young, a senior postdoctoral researcher at the university's Nerve Gut Research Laboratory.

In Hong Kong, a number of artificial sweeteners are permitted for food use, including Ace K, aspartame, cyclamate, saccharin and sucralose.

The law requires that such food additives must be listed by their functional classes and specific names or identification numbers on food labels.

The EFSA was asked to fully re-evaluate aspartame after European MPs raised concerns.

Aspartame is made up of two amino acids: aspartic acid and phenylalanine. When digested, aspartame is broken down into its constituents.

Because of this, people with phenylketonuria (PKU), a metabolic disorder that stops the breakdown of phenylalanine, should avoid the sweetener. Phenylalanine builds up in the blood of PKU sufferers and can affect the brain and lead to seizures and other serious medical issues. But for everyone else, aspartame has been deemed by health authorities to be safe.

The EFSA's panel on food additives and nutrient sources added to foods reviewed nearly 2,000 studies and datasets from the 1960s to the present that were "produced to internationally recognised scientific standards".

In addition, it held a public consultation, receiving more than 200 comments from the public, non-governmental organisations, academics, national food safety agencies, and journalists.

Two studies on aspartame published in 2010 stood out. The first study claimed that pregnant Danish women who consumed artificially sweetened soft drinks had an increased risk of pre-term delivery.

The second study, from Italy, claimed that aspartame could cause lung and liver cancers in male mice that were fed the artificial sweetener throughout their lives.

Previous complaints about aspartame included headaches, allergic reactions, behavioural changes, and cancers of the blood and brain. But the panel found that there was either no or little evidence for any of the concerns.

For the 2010 study of Danish pregnant women, the ESFA found that "there is no evidence available in this study to support a causal relationship between the consumption of artificially sweetened soft drinks and pre-term delivery."

A more recent study from 2012, conducted in Norway, found a "barely discernible association" between artificially sweetened soft drinks and pre-term delivery.

As for the second 2010 report claiming that aspartame caused cancer in male mice, the ESFA concluded that "the validity of the study and its statistical approach cannot be assessed and its results cannot be interpreted".

Another conclusion was that the breakdown products of aspartame - aspartic acid, phenylalanine and methanol - exist naturally in fruit and vegetables.

The exposure to these compounds from consumption of aspartame was low.

"This opinion represents one of the most comprehensive risk assessments of aspartame ever undertaken," said Alicja Mortensen, who chaired the panel.

But do artificial sweeteners help to curb sugar consumption? A study by Yale University of School of Medicine published in September last year found that it is hard to fool the brain by providing it with "energy-less" sweet flavours, leading to a higher likelihood of sugar consumption later.

The study, conducted on mice, identified a specific physiological brain signal that is critical for determining choice between sugars and sweeteners.

This signal regulates dopamine levels - a chemical necessary for reward signalling in the brain - and only arises when sugar is broken down into a form where it is usable as fuel for cells of the body to function.

"According to the data, when we apply substances that interfere with a critical step of the 'sugar-to-energy pathway', the interest of the animals in artificial sweetener decreases significantly, along with important reductions in brain dopamine levels," says the study's lead researcher, Professor Ivan de Araujo.

"This is verified by the fact that when hungry mice - who thus have low sugar levels - are given a choice between artificial sweeteners and sugars, they are more likely to completely switch their preferences towards sugars even if the artificial sweetener is much sweeter than the sugar solution," de Araujo says.

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Common artificial sweeteners

Brand names: Sunett, Sweet One

• A combination of an organic acid and potassium, it is about 200 times sweeter than sugar.
• Used in food and drinks, and as a tabletop sweetener.
• Heat-stable and can be used in cooking.

Brand names: Equal, NutraSweet

• A molecule consisting of two amino acids - phenylalanine and aspartic acid.
• About 200 times sweeter than sugar.
• Not heat-stable and therefore not suggested for use in cooking.

Brand names: Sweet'N Low, Sweet Twin, Necta Sweet

• Oldest low-calorie sweetener approved for food and drink use.
• About 300 times sweeter than sugar.
• Used in many diet foods and drinks; may have a bitter or metallic aftertaste.
• Brand names: Splenda
• Made from a process that begins with regular table sugar (sucrose).
• About 600 times sweeter than sugar.
• Heat-stable and therefore used almost anywhere sugar is used, including in cooking.