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Are diet foods bad for your memory?

Psychologist Tim Barth studies the effects of aspartame.

By Rick Waters '95

Since the artificial sweetener aspartame (commonly found in NutraSweet and other products) became popular as a sugar substitute, some weight-conscious users have complained of memory problems and headaches that disappear when they cut it from their diet.

No study has ever confirmed this link, but Timothy Barth, chair of TCU's psychology department and an expert on brain injuries, got to thinking -- people who suffer head traumas occasionally experience lapses in memory function. Could there be a connection?

Barth believes so. Immediately following an injury, the brain releases an excess of neurochemicals that limit its ability to prevent toxic chemicals from accumulating, and that can lead to additional brain damage. One of those chemicals is similar to a metabolite called aspartic acid, which the body makes after taking aspartame.

"So for anyone who consumes aspartame right after brain injury, that might exacerbate their behavioral problems," Barth says.

For the rest of us, our memory concerns may be psychological. A person dieting because of low self-esteem and anxious about memory function might be prone to perceived memory problems.

Research has been controversial. NutraSweet-funded studies show no connection to memory problems, while independent studies indicate otherwise. Barth believes more study needs to be done with at-risk groups and long-term users.

To help sort out the possibilities, his team gave 90 students a nutrition survey and a memory questionnaire before they took short-term memory tests. Aspartame users reported more memory problems than nonusers, especially forgetting to perform a task at a certain time or forgetting a regular routine.

However, on short-term memory tests, such as remembering a word list, phone numbers or a series of faces, everyone performed about the same.

But Barth's most telling research was done with rats and their recovery after brain injury. He found that rats fed aspartame struggled with daily sensory motor tests while those that didn't take aspartame recovered in about 10 days.

"We think that after two weeks, the blood-brain barrier should be working more efficiently, and the release of neurochemicals should be over," Barth says. "So we hypothesized that if we administered the testing two weeks after injury, instead of right after, there should be no difference in the groups.

Further tests confirmed this. "They seemed to suggest that aspartame may slow down the recovery process, and if you wait long enough the behavioral function may return to normal."

The team repeated the process with monosodium glutamate, which is similar in structure to aspartame. Same results. Barth says that the three studies together "converge on the idea that food additives, when consumed, may be a problem right around the time of brain injury."

Barth plans to publish his findings in the Journal of Neurotrauma but only after long-term testing.

Contact Barth at