Many of those Searle studies that Gross questioned are now lumped into the data that says aspartame is safe. And though the question of aspartame causing brain tumors has largely been dismissed over the years, there hasn’t been much new data on the subject. In fact, a 1987 General Accounting Office report states that 28 out of 69 scientists said more research was needed in the areas of “neurological functions, brain tumors, seizures, headaches, and adverse effects on children and pregnant women.” Nonetheless, the report added, research was ongoing in all areas except brain tumors. What’s more, the FDA dissuaded the National Toxicology Program (NTP) from doing further cancer research on aspartame. As the founder of the NTP, David Rall, put it, “It’s a wonderful way to ensure that it isn’t tested—discourage the testing group from testing it and then say it’s safe.”
…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.