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Aspartame and Animal Models

Steven Novella MD, has written an excellent article about aspartame: Aspartame – Truth vs Fiction. The article is on the Science-Based Medicine website, a website I have recommended several times. I will not summarize Novella’s comments as I think the article should be read in its entirety. I will comment however on one aspect of the aspartame controversy.

Aspartame is an artificial sweetener that was synthesized in 1965 and approved by the FDA in 1974. It is broken down to numerous chemicals one of which is phenylalanine, and therefore people with phenylketonuria (PKU) must avoid products containing aspartame. Otherwise it appears pretty safe.

And that’s where the controversy comes in.

Based largely on experiments with rodents, aspartame has been linked to a number of condition and symptoms. The medical literature clearly shows that aspartame is safe for most people. Some headaches have been attributed to aspartame but many chemicals and situations can trigger headaches so that is nothing to get excited about (unless you are the headache sufferer in which case you should avoid aspartame). But animal studies have revealed that aspartame can cause adverse reactions and conditions, some of which could be life threatening. Other animal studies have not shown these reactions. Suffice it to say the animal-based research literature is mixed.

This gets me to my usual point; animals cannot predict human response to drugs and disease. But it also illustrates another point I make, but usually less explicitly. Different animals also react differently. There is variation among species as well as within species. One strain of mouse may react to a drug very differently than another strain. What this means is that if you are a drug company and want to show that your drug is safe, you can always find a strain or species of animals that can take kilograms of the drug without adverse reactions. On the other hand, if you are making a competitor to that drug your company can find a strain or species that manifests like threatening reactions to your competitor’s drug. Everybody wins.

Of course, when everybody wins nobody wins and that is exactly the case here. The purpose of using animals in most forms of research, but especially in drug testing, is to predict human response. Examples like aspartame demonstrate the futility of this. (See Animal Models in Light of Evolutionfor the science behind this and FAQs About the Use of Animals in Science: A handbook for the scientifically perplexed for more accessible examples.) When different species and strains respond very differently, one must question the value of using animals to test for human response. Further, science has not figured out how to pick the correct species before human testing. Even when the mechanisms of metabolism for the drug are known and a species can be found that reproduces this, scientists cannot get around the fact that humans and animals are differently complex. Yes, animals are intact systems but they differently intact from humans. As I have said many times, very small differences between intact complex systems can negate the many similarities.

I am not the only one that has figured this out. Patients and patient advocacy groups are also questioning the utility of animal models. For example, Megan Rechin has written a nice article on the Myelin Repair Foundation’s website. I wrote a short comment following the article.

(My recommendation of a website or article should not be misconstrued as implying that the website or author agree with me on the issue of animals in research.)


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