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Since 1982, Diet Coke has been the preferred drink of many millions of people. In fact you probably know at least one person who drinks at least 3 cans of the sugar-free nectar just to get through the day. Diet coke addiction is rife; there are multiple 12 step programs available for those who feel their intake has reached worrying levels and want to ditch the habit. But should they be worried? The origins of the low calorie soft drink were harmless enough. It was originally developed in response to the worrying concern that a can of regular ‘full-fat’ Coke contains approximately 10 teaspoons of sugar (40.5g). Maintaining the sweet taste was no mean feat. Diet Coke uses the artificial sweeteners aspartame and acesulfame-K instead of the high fructose corn syrup used in regular Coca-Cola. Combined, they give a more sugary taste than aspartame alone.
But what is this ‘aspartame’? It sounds like a horrible, man-made chemical! Well, Aspartame is a non- saccharide sweetener which has been used as a sugar substitute since 1974, when it was first approved for use by the Food and Drug Administration (FDA) in the USA. It was discovered by a happy accident in 1965, when chemist James M. Schlatter was working on an antiulcer drug and licked his finger to turn a page. Instead of getting a nasty shock the chemical he had made was incredibly sweet. He had made aspartame which is 200 times sweeter that regular sucrose; it is not calorie free but the amount required to produce the same sweet taste as sucrose is so small it contributes practically nothing to the calorie content of an end product. As an added bonus it does not exacerbate tooth decay, keeping dentists everywhere happy!
The safety of aspartame has come under no end of scrutiny; most famously it was attacked by Ms Nancy Markle (a pseudonym, as it turned out) in her summary of the World Environmental Conference in 1999 where it was attributed to side effects ranging from cramps to blurred vision to vertigo. Most commonly it is accused of causing cancer and weakening bones. A quick Google of the “aspartame risks” will take you 131,000 websites informing you of the dangers of aspartame disease; one website will inform you of a rehab clinic dedicated to helping patients shake the effects of aspartame use.
Few of these anti-aspartame sites are supported by substantial amounts of research data, and many are just scare mongering, they do however stem from a real concern that when aspartame metabolises in the body the component parts will cause a toxic build up. It is this thought process which has lead to the miscommunication of certain scientific fact in the media. What is perhaps most worrying is that the science behind these claims is often logical enough to convince some of a toxic nightmare.
The chemistry of aspartame is relatively straight forward; it is a methyl ester of aspartic acid and the phenylalanine dipeptide. Once ingested it is broken down immediately into its three separate chemicals: aspartate, phenylalanine and methanol. Thus aspartame itself never enters the bloodstream; any suggestion aspartame is an ‘evil-doer’ tends to ignore this fact. It is the toxicity of the component parts which has raised concerns over the safety of aspartame as a sweetener. On its own aspartate has been shown to cause neuronal necrosis, phenylalanine to cause mental retardation in PKU sensitive people and methanol at high levels can lead to blindness.
The effects of methanol have been studied both when it is ingested on its own, or as a by-product from aspartame hydrolysis. Large quantities of methanol directly increase both the blood methanol and formate concentrations. A dose of 10mL of pure methanol can cause immediate blindness while the lethal dose is 100mL. This logically would mean a danger to those with high blood methanol levels, potentially causing metabolic acidosis; a condition with symptoms including rapid breathing, confusion and lethargy. While this all sounds very dramatic, it should not be forgotten that methanol is also released into the body after the eating of fruit and the drinking of fruit juice. To put it in context a 250ml glass of juice will provide 4-6 times more methanol than the same volume of Diet Coke. Yet we are encouraged to drink fruit juice as part of our 5 a day intake. The human body is more than well equipped to deal with the small amount of methanol released in the digestion of food and drink. Our livers convert methanol into formaldehyde which is only ever used by the body and not stored, if there is excess formaldehyde that the body does not need it then it will be converted to formic acid which in turn is excreted in the urine or broken down to carbon dioxide and water.
The second by-product, aspartate, was thought to exert toxic effects because it is an excitatory amino acid. As you might have guessed, excitatory amino acids can “excite” the neurotransmitters so much that they become damaged, resulting in memory loss and aggravating conditions such as Parkinson’s disease. Another hypothesis was that individuals sensitive to MSG (another excitatory amino acid), given the nickname ‘Chinese restaurant syndrome’, would also be affected by of aspartame. However, similarly to methanol, no side effects were exhibited when various groups were given high doses of aspartame. Aspartame loading occurs when the next dose of aspartame is ingested before the blood plasma levels of the by-products have returned to normal. As most sugar free beverage drinkers will consume multiple cans, glasses, or gallons over a 24 hour period, the idea of aspartame loading was investigated. Yet again, none of the side effects listed above were experience, nor did aspartame loading have a significant effect on the plasma aspartate concentration.
Finally, the last and most dangerous component of aspartame: phenylalanine. While normally found in the brain, excessive levels of this chemical is linked to mental retardation in persons with PKU. Phenylketonuria or PKU is the inability to process proteins properly leading to a build up in phenylalanine. While this is a genetic disease and those with it would know to stay away from food stuffs which produce phenylalanine a common misconception among the anti aspartame groups is that phenylalanine affects people without PKU in the same way, potentially causing seizures. Yet again these claims have been shown to be false, even with the highest levels of aspartame 200mg/kg/day and with multiple aspartame loading throughout a 24 hour period; the small increase in plasma levels of phenylalanine poses no significant risk.
All of the tests have been carried out to the highest aspartame levels, a dose of 200mg/kg body weight; no ill effects have been documented from this high dosage. This level of aspartame equates to 106 cans of soft drink each day, with the best will in the world, this Diet Coke loving writer could not consume 35 litres of the sugar free drink daily but even if someone could manage this task they would still not experience any of the supposed side effects.
In the UK aspartame was first approved by the Food Standards Agency in 1982, this has since been reaffirmed in 1992, following the publishing of new literature confirming the original findings of the UK’s Committee on Toxicity, Consumer Products and the Environment (COT). Yet again in 2001, over 500 papers were reviewed by the Scientific Committee on Food (SCF) concerning the safety of aspartame and its adverse effects. The widespread use of aspartame has been approved in over 90 countries worldwide, and the safety of aspartame has been affirmed by the FDA 26 times in the last 23 years. The research is there, and it is very clear: aspartame at normal or elevated levels is not a danger to any persons’ health.As put by Lewis D Stegink
The science of toxicology is based on the premise that all compounds are toxic at some dose. Salt, water, sugar and even a mother’s love produce deleterious effects when given in inappropriate amounts.
Lewis D Stegink
Critical Reviews in Toxicology DOI: 10.1080/10408440701516184 http://www.ajcn.org/content/46/1/204
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