Aspartame and Formaldehyde
Aspartame is an interesting molecule, more closely related to a protein than a sugar. It is formed of two amino acids (phenylalanine and aspartic acid) and a methyl ester. Our body metabolises it completely in the intestinal tract to its amino acid components and methanol, which is reduced by our body to formaldehyde and then formic acid. Because it is easily and fully metabolized, it is unlikely to enter our bloodstream whole.
One issue often raised is that one of the metabolites of aspartame is methanol, which accounts for about 10% of the broken down molecule. Methanol is poisonous to our body, but we are equipped to deal with it in small amounts. Once methanol reaches the liver, it is converted enzymatically to formaldehyde which is then mostly converted to formic acid, the substance to which all aspects of methanol poisoning are attributed. Methanol is found naturally in many fruits and vegetables as well, but it is found in conjunction with higher amounts of ethanol, which utilizes the same enzyme as methanol. When methanol is unsuccessfully converted, it is excreted harmlessly through our urine.
Many notable proponents of aspartame, including groups such as the Academy of Nutrition and Dietetics (formerly the American Dietetic Association, or ADA), argue that our body is equipped to rapidly metabolise methanol and formaldehyde, and that formaldehyde is actually a useful building block in small amounts.
To argue that formaldehyde is a useful building block in small amounts is like saying arsenic can be a useful building block–both formaldehyde and arsenic are used by our body in extremely small amounts, but they’re also both toxic when those amounts rise. Our body has enough formaldehyde naturally present to build anything it might need, consuming more will not provide any benefit.
Studies of smokers, who inhale formaldehyde directly into their system, demonstrate the potential dangers of even a very small amount of excess formaldehyde. A cigarette contains roughly 20 micrograms of formaldehyde, which once inhaled will be completely metabolised within 1-2 minutes. The problem is that the formaldehyde also very rapidly forms compounds known as formaldehyde-DNA adducts, which basically means the formaldehyde attaches itself irreversibly to our DNA.
In a healthy individual, these compounds would form rarely and be destroyed by safety measures built into our system, such as apoptosis (programmed cell death). In individuals who form a lot of these compounds, due to increased exposure to formaldehyde, they may end up building up and could play a role in the onset of certain cancers.
How Nutrasweet Can Damage Our DNA
The amount of methanol in a pack of Nutrasweet, once metabolized by our gut, is 3.5 milligrams, which is 3500 micrograms. Processed in our the liver, the vast majority of this methanol will end up as formic acid, but first the methanol is converted to formaldehyde. Once converted from methanol, formaldehyde is very rapidly turned into formic acid. Remember in the case of the cigarettes, though, that these formaldehyde-DNA adducts formed in less than a minute! We may not have a very long exposure to formaldehyde, but research suggests it doesn’t take very long or very much to damage the DNA!
One study demonstrated that this does indeed happen with ingestion of aspartame. The methanol portion of the molecule was labeled, so it could be tracked. This label is designed to remain even after the methanol is converted to formaldehyde or formic acid. In amounts of 20 mg/kg, 5% of the label remained after five hours, half of that in the liver. When the dose was increased to 200 mg/kg, even more was found, so the effect is thought to be dose-dependent and a contributor to the amounts of formaldehyde-DNA adducts formed.
20 mg/kg is a lot of aspartame, equivalent to 9-10 cans of diet soda a day for an average-weight female, but the formaldehyde-DNA adducts are formed irreversibly–once formaldehyde binds to the DNA of a cell, the only way to get rid of it is for the cell to die. If aspartame can cause the formation of these compounds, then even a small amount daily could contribute to a growing effect. 5% of 3500 micrograms (the methanol content of one pack of Nutrasweet) is 175 micrograms, which suggests that when all the metabolizing is done, 175 micrograms of formaldehyde might have remained behind, bound to your DNA. Don’t forget, the cigarettes mentioned earlier only contained 20 micrograms!