In 1996, John Olney, a professor of pathology and immunology at Washington University Medical School, claimed to have found epidemiological evidence that the introduction of aspartame in the US was connected to an increase in an aggressive form of brain tumor called glioblastomas. But this was criticized for just being a correlation and dismissed by the FDA.Then, from 2006 to 2010, the Ramazzini Institute in Italy published three papers with evidence of cancers in laboratory animals exposed to aspartame. In the longest and largest study, which went on for seven years in 1,900 rats, researchers found surprisingly high rates of lymphomas, leukemias, and other tumors, including kidney tumors. A follow-up study in 2007, which exposed mice to aspartame in the womb and through the entire lifespan, found the same kinds of cancers in addition to breast cancer. A third study in 2010 found cancer of the liver and lung in male mice. These findings provoked controversy as well, with questions swirling about the laboratory itself. Industry quickly criticized the findings for alleged flaws in the research.The Center for Science in the Public Interest (CSPI) conducted a detailed investigation into the findings reported by the Ramazzini Institute, filing FOIA requests for further information. Lisa Lefferts, senior scientist at CSPI, said they found the criticisms to be entirely without merit, and characterized the findings this way: "There is consistent evidence from well-designed, independent studies that aspartame causes cancer in animals and therefore, it may also cause cancers in humans. It is pretty compelling evidence and we recommend that consumers avoid it."
A longterm study in humans found a positive association between aspartame intake and risks for non-Hodgkin lymphomas and multiple myeloma in men, and leukemia in both men and women.
The checkered history and scientific findings on the sweetener raise a lot of concern—but these aren't the only factors to consider. What about its stated purpose: to reduce calorie consumption, aid in weight loss, and perhaps lower diabetes risk?It's well established that there is a correlation between being overweight and diet soda consumption, but the question is which way the association works. Do people who are overweight tend to drink diet soda, or is something about the diet soda contributing to weight gain? A 2015 study found that long-term consumption was associated with increased waist circumference. And a 2016 study found that mothers who consumed diet soda while pregnant had babies with a two-fold higher risk of being overweight at age one.While the question of whether the sweetener causes weight gain, diabetes, or other metabolic disease is unsettled, there are some remarkable correlations. A 2013 Purdue review over 40 years found that people who regularly consume artificial sweeteners are at increased risk for obesity, type 2 diabetes, metabolic syndrome, and cardiovascular disease. A 2013 analysis of more than 66,000 women showed that consumption of both sugar-sweetened beverages and artificially-sweetened beverages was associated with increased risk for type 2 diabetes. And another major finding came when researchers from Harvard Medical School analyzed data from the Nurse's Health Study and found that women who drank more than two artificially sweetened sodas per day had a twofold increased risk for kidney function decline over two decades.
"Am I concerned? Absolutely," Lustig says. "Would I drink the stuff? No way in hell."