Here's everything you need to know about aspartame, the mysterious ingredient which people think causes cancer

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There’s nothing quite as satisfying as a cold, carbonated drink to quench your thirst. And if that drink happens to be deliciously sweet? Well, perfect. But the truth behind why many of our foods are so sweet is alarming experts.

Eminent physician Dr Joseph Mercola is one of many medical professionals who believes that aspartame - an artificial substance 200 times sweeter than sugar - should be avoided.

Cans of soda Credit: Getty

You may not know you are eating it and in the European Union, it is codified as E951. The sweetener, which the body breaks down into phenylalanine, aspartic acid and methanol, was the subject of Dr Mercola's book entitled Sweet Deception: Why Splenda, NutraSweet, and the FDA May Be Hazardous to Your Health.

As his website explains: "Aspartame accounts for over 75 percent of the adverse reactions to food additives reported to the FDA. Many of these reactions are very serious, including seizures and death."

Scientists test aspartame Credit: Getty

The substance's purported low-level side effects include headaches, dizziness, rashes and weight gain. As an alternative to sugar, aspartame is in a wealth of foods including drinks, cereals, chewing gum and tabletop sweeteners.

"Dr. Russell L. Blaylock, a professor of neurosurgery at the Medical University of Mississippi, recently published a book thoroughly detailing the damage that is caused by the ingestion of excessive aspartic acid from aspartame," states Dr Mercola's website. "Blaylock makes use of almost 500 scientific references to show how excess free excitatory amino acids such as aspartic acid and glutamic acid (about 99 percent of monosodium glutamate or MSG is glutamic acid) in our food supply are causing serious chronic neurological disorders and a myriad of other acute symptoms."

A slice of lemon in a fizzy drink Credit: Getty

"Aspartate and glutamate act as neurotransmitters in the brain by facilitating the transmission of information from neuron to neuron," it goes on to say. "Too much aspartate or glutamate in the brain kills certain neurons by allowing the influx of too much calcium into the cells. This influx triggers excessive amounts of free radicals, which kill the cells. The neural cell damage that can be caused by excessive aspartate and glutamate is why they are referred to as 'excitotoxins.' They 'excite' or stimulate the neural cells to death."

However, governing bodies such as the FDA (Food and Drug Administration) and EFSA (European Food Safety Authority) agree that aspartame is not dangerous in most cases. Yet since it was introduced to European countries in the 1980s, it has been the subject of much controversy.

Aspartame molecule Credit: Getty

A 1996 study seemed to suggest a link between aspartame and an increase in the number of diagnosed brain tumours. However, this study had very little scientific basis with more recent studies suggesting otherwise.However, the European Ramazzini Foundation of Oncology and Environmental Sciences published several long-term studies between 2006 and 2007 which linked aspartame with an increase in cancers in rats. The consumption of aspartame in rats, it suggested, positively affected the development of lymphomas and leukaemias.

Cola pouring into a glass Credit: Getty

However, in 2006 the US National Cancer Institute commissioned a study involving almost half a million test subjects. The investigation compared those who consumed drinks containing aspartame with those who did not. The results showed that those who consumed aspartame did not have an increased risk of leukaemia, lymphoma or brain cancer.

Aspartame, despite being the subject of many chain emails and scare stories, is now generally considered safe. That said, those suffering from a rare genetic condition called phenylketonuria (PKU) cannot break down phenylalanine and should therefore avoid it.

A clear, carbonated drink in a bottle Credit: Getty

An EFSA report stated: “PKU mothers with poorly controlled phenylalanine intake in their diet during pregnancy may give birth to babies with congenital heart diseases, microcephalus and impaired neurological function.”

There are plenty of opposing views on the subject, with many people saying it should be avoided. However, the majority of medical professionals would tell you that it's safe, as long as it's consumed within the 40-milligrams-per-kilo-of-bodyweight limit.

A fizzy drink in a glass Credit: Getty

The fact is, there are probably far more harmful things in your lifestyle. In fact, the World Health Organization classes bacon as a group one carcinogen - the same category as cigarettes and asbestos (though it should be noted that eating bacon is clearly not as harmful).

However, while some things which have generally been considered to exist within a grey area are actually widely considered to be safe, there are other substances which are generally considered harmful but which are actually harmless. For example, the story of how MSG came to be considered dangerous is a tale of disinformation, distrust and xenophobia.