Aspartame
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Text Box: Aspartame/ NutraSweet/ Equal   Classification ADI ADI CEDI CEDI Aspartame Nutritive Sweetener; 4kcal/gm 50mg/kg body wt/day according to FDA; 40mg/kg body wt/day according to EFSA About 20 cans of diet soda estimated highest average use is 13.96 gm/kg body wt/day about 12 yogurts (170gm size) or 5.5 cans of diet soda Metabolism: Aspartame is broken down in the gut to phenylalanine, aspartic acid, and methanol.  Aspartic acid and phenylalanine are amino acids, the building blocks of proteins. Methanol is an alcohol that is rapidly converted by the liver to formaldehyde, which is then rapidly converted to formic acid.  Formic acid has a half life of several hours in the body and is excreted in urine. Proposed theories of toxicity: Methanol: Formic acid is actually the culprit in methanol toxicity and can cause acidosis, eye injury, and central nervous system depression at very high doses.  In at least one study, the level of methanol in the blood after ingestion of even large doses of aspartame was much lower than that known to cause toxicity.  And, after consumption of the amount of aspartame in about 15 diet 12 oz. soft drinks, the amount of methanol in the blood of human test subjects was below the detectable level.  All of that being said, consider that the EPA has set the safe daily intake level (RfD, like the ADI) for methanol at 0.5mg/kg/day, or 35mg for a 70 kg person.  One liter of diet soda has been estimated to lead to 55 mg methanol upon consumption.  That means that one 44oz Big Gulp surpasses the RfD for methanol. Studies have not, however, demonstrated a toxicity with this level of consumption. Phenylalanine, an amino acid, is toxic to a specific population of individuals who have phenylketonuria, a disease typically diagnosed at birth in the United States. Aspartame is not approved for phenylketonurics and they should not ingest it. Aspartic Acid: There also exists an hypothesis that the aspartic acid from aspartame metabolism could cause damage to the brain. This theory proposes that after consumption, blood levels of aspartic acid spike. Aspartic acid is an amino acid, a building block of proteins, that is also an excitatory neurotransmitter. It is hypothesized that spikes in aspartic acid would lead to high concentrations of aspartic acid in areas unprotected by the blood brain barrier and that these high levels could lead to excitotoxicity and death of neurons.  Fetuses and infants with immature blood brain barriers would be particularly at risk, as would anyone with any number of illnesses that would make the blood brain barrier leaky.  What role this hypothesis plays in case reports of aspartame linked to headaches, seizures, ADHD is unknown.  Cancer: Additionally, some studies have linked aspartame to cancer in laboratory rodents.  In recent years, Dr. Soffritti and colleagues of the European Ramazzini Foundation of Oncology and Environmental Sciences have found that prenatal and lifetime exposure to aspartame at levels slightly higher to much higher than the ADI have lead to an increase in lymphoma, leukemia, bladder, and mammary tumors in their laboratory rats. The EFSA (European Food Safety Authority) challenged this research by stating that the rat colony in question was for some reason, perhaps due to a viral infection, more prone to tumors than other rats. The EPA has recently reviewed the Ramazzini Foundation research and has not found that to be the case. In a paper published in Environmental and Molecular Mutagenesis, Jane Caldwell of the EPA discovered no reason, other than the treatment given in the study, for the animals to have an increase in tumors. To my knowledge the FDA has not acted on this finding. This is just a sampling of the proposed theories of aspartame toxicity, there are many more.