Ajinomoto Group AJINOMOTO GROUP Worldwide

Psychology Today

University of Pittsburgh
UPMC Health System Weight Management Center
3811 O'Hara Street
Pittsburgh PA 15213-2593

Robert Epstein, Ph.D.
Psychology Today
11th Floor
49 E. 21st St
New York, NY 10010

Dear Dr. Epstein:

I would like to comment on the article "Dangerous Diet Drinks" that appeared in the March/April 200l edition of Psychology Today. This article was based on the result of a study conducted on a group of college psychology students that was reported as an abstract at a scientific meeting last fall. The abstract states that self-reported use of aspartame among college students was associated with an impairment of one measure of memory. The authors suggest that the perceived effect may be related to the accumulation of aspartame metabolites in the nervous system. In considering this abstract, which has not been reviewed by scientific peers for reliability of design, your readers should consider several facts:

First, the study apparently relied on self-reports of aspartame use (via a nutrition survey) to determine who ingested the sweetener. No indication is given as to whether use levels of aspartame were assessed. It is a well-established fact that dietary recall (i.e., self-report) is notoriously unreliable as a method for establishing nutritional and dietary habits. Hence, it is not possible from the design of this study to know if those who reported using aspartame actually did, or how much they consumed. Moreover, it is not possible to know if those who reported not using the sweetener actually did not consume it. The basis for distinguishing users from non-users is thus unreliable: we cannot accurately pick out the aspartame users from the non-users in this study.

Second, we are not provided with any information regarding subject selection, other than reported use of aspartame. Hence, we cannot know if other important features of members of each group could account for the presence or lack of effects.

Third, the investigators attribute the memory effect they saw to the build-up of aspartame metabolites in the nervous system. These metabolites are methanol, aspartate and phenylalanine. It should be noted that a substantial body of research, conducted in humans in the 1980's, showed that none of these aspartame break-down products accumulates in the blood, even under conditions of extremely high levels of intake. For these compounds to accumulate in the nervous system, they must first pass through the blood. Since no increases in their levels in blood occur, there can be no increases in their levels in the nervous system. Thus, there is no build-up of aspartame metabolites.

Fourth, a number of carefully-designed, published studies in humans have shown the absence of nervous system effects of aspartame. To reopen this issue some 12-15 years later, one would expect that an investigator would undertake a study of extremely careful design, to insure a convincing outcome against this impressive, earlier literature showing no effects. Such appears not to be the case in the study that is the object of the column.

In my opinion, therefore, given the clear utility of caloric substitutes like aspartame in helping individuals to control their weight, to reduce tooth decay, and to maintain a low blood sugar level (very important for diabetics), the public is not well served by raising concerns about aspartame safety based on a very flawed study.


John D. Fernstrom, Ph.D.
Professor of Psychiatry, Pharmacology & Neuroscience
Research Director, UPMC Health System Weight Management Center
University of Pittsburgh
3811 O'Hara Street
Pittsburgh PA 15213-2593

9 April 2001