Diet experts voiced skepticism over new claims that aspartame poses a risk to the millions of people who consume it daily.
The Center for Science in the Public Interest, a nutrition and food safety advocacy group, called on the U.S. Food and Drug Administration to review the claims, which stem from research conducted by the European Ramazzini Foundation in Italy.
The foundation reported that rats who consumed aspartame in exceedingly large quantities were more likely to develop cancer. CSPI executive director Michael Jacobson considers this an important finding that should not be overlooked.
"I don't think consumers should panic, but the FDA should take the results of the new study very seriously. ...The new study won't be easily dismissed."
FDA spokesman Michael Herndon said that to date, the agency has not received any data from the new study, and therefore cannot comment on the findings.
However, he noted in a statement, "[T]he conclusions from this second European Ramazzini Foundation are not consistent with those from the large number of studies on aspartame that have been evaluated by FDA, including five previously conducted negative chronic carcinogenicity studies.
"Therefore, at this time, the FDA finds no reason to alter its previous conclusion that aspartame is safe as a general purpose sweetener in food."
Dr. David Katz, director of the Prevention Research Center at the Yale University School of Medicine, said he believes the new research will not change this conclusion, noting, "I do not have the impression this study changes the lay of the land."
He suggests that if aspartame were causing cancer in humans, agencies like the Centers for Disease Control and Prevention would have seen a dramatic rise in cancer rates since the artificial sweetener hit the market in 1981.
"Millions of people are exposed to high doses of aspartame daily, which means we have an enormous amount of observational data in humans," he said. "If aspartame were going to cause a meaningful uptick in human cancers, we've had a natural experiment -- namely, the continuous tracking of cancer trends by CDC -- to show us that movement of the needle. To date, it has not been seen."
Others also have doubts.
"This institute has issued very flawed studies in the past," said Keith-Thomas Ayoob, an associate professor and nutritionist at the Albert Einstein College of Medicine.
"The European Food Safety Authority, and many others, have discredited past studies by this institute, due to serious flaws," he said. "They presented this data months ago in New York but wouldn't let the study be reviewed before they made their announcement, or even after. It makes you wonder why."
A Tasty Target
The controversial new study was published in the June 13 issue of the journal Environmental Health Perspectives. In their report, the researchers from the Ramazzini Foundation gave aspartame to rats every day, starting before they were born; they suggest this is similar to how humans consume the food additive.
Some rats were given aspartame in an amount equal to twice the daily intake approved by the FDA, which would be about the same as 37.5 cans of diet soda per day for a 150-pound adult.
Others rats were given a lesser amount -- about 7.5 sodas for an adult, or 2.5 soft drinks per day for a 50-pound child.
The rats who consumed this lesser amount, similar to what many Americans consume in a day, did not show significantly increased rates of cancer.
The group given higher amounts, however, was found to have more tumors. Overall, the study authors suggest that the more aspartame a rat consumed, the higher its risk of cancer.
Experts, however, remain unconvinced.
"If the investigators examined the incidence of many different types of tumors, one would expect one to two to be significantly increased by chance alone, i.e., random, not real," said Susan Fisher, director of the division of epidemiology in the Department of Community and Preventive Medicine at the University of Rochester Medical Center.
Katz was also not swayed by the study's claims that rats that consumed more aspartame had higher rates of cancer in their blood and lymph nodes.
"We know that rats consistently exposed to fairly high doses of aspartame develop more leukemia and lymphoma, although these conditions are common in rats anyway," he said. "For all we know, exposing them to a high daily dose of sugar might do the same."
Sour Over Sweetener
This recent study was a follow-up to research published by the European Ramazzini Foundation in 2005 and 2006. The older experiments started rats on aspartame later in life, at 8 weeks old, and included much higher doses of the sweetener.
In response to these previous studies, the European Food Safety Authority reviewed relevant evidence from the United States National Toxicology Program and the United States National Cancer Institute and found no basis for the claim that aspartame would cause cancer in humans.
In April of this year, the FDA also stated that the studies in rats did not support the group's conclusions that the sugar substitute would raise human cancer rates.
Although experiments in rats are often done to test how chemicals will affect humans, some experts do not believe the results from one species will always translate to another.
"There are still questions regarding the similarities between rats and humans," Fisher said. "The animal model may not be perfectly analogous to what we may expect in humans."
Alan Wu, director of the chemistry and toxicology laboratories at San Francisco General Hospital, echoed that sentiment.
"Certainly, you can't make a generalization that it's always applicable; there are differences between species, human and rats, in how they deal with drugs," he said. "Toxicity in one species may not occur in the other."