I’m sure you’ve seen the studies that come out from time to time showing that diet sodas are arguably kinda-sorta bad for you. (Their evidence is never very strong.) But did you see the new study that found diet soda was better than water for people with type 2 diabetes? Not only is it a real study, it was well-designed and we should be paying attention to it, according to an epidemiologist I talked to who was not involved in the study.
That epidemiologist is Gideon Meyerowitz-Katz of the University of Wollongong, who wrote about it here. When I asked him if it was a good or a bad thing that this study had mostly escaped notice by news media, he said “this is far more robust than most of the science that gets media coverage.” The study was not sponsored by any commercial drink company.
What the study found
In the delightfully named SODAS trial (Study Of Drinks with Artificial Sweeteners), researchers at the University of California, Irvine, and the University of Minnesota, Minneapolis, recruited adults who had type 2 diabetes and who had a habit of drinking artificially sweetened beverages (including, but not limited to, my one true love Diet Coke). The study was funded by the U.S. National Institutes of Health’s National Institute of Diabetes and Digestive and Kidney Diseases.
Half of them were asked to switch to drinking water instead, and everyone was provided with three servings a day of either their diet drink of choice, or a water of their choice (unsweetened seltzer included). The study ran for 24 weeks. There were 181 people enrolled, of which 179 finished the study, which is considered a fairly large group for a study of this type. (It’s twice as large as an older study I’ll contrast it with below.)
The main outcome the researchers studied was hemoglobin A1C (HbA1C) as measured by a blood test. This is a common test used to monitor glucose control in people who have diabetes or are at risk for it. The higher your HbA1C, the higher your blood glucose has probably been over the past three months or so.
The results: HbA1C got slightly better in the group that was drinking artificial sweeteners: from 7.19% to 7.14%. It got worse in the group that was drinking water, from 7.20% to 7.44%.
The researchers collected a few other metrics, for good measure. Fasting glucose, fasting insulin, and “time in range” as measured by a continuous glucose monitor all favored the diet drinks group. The people in the diet drinks group lost a little bit of weight (on average, two pounds) while those in the water group had stable weights. The researchers referred to this difference in weight loss as “statistically significant, but not clinically significant.” In other words, probably real, but too small to matter.
Bottom line: there was no real benefit to the people in the study switching from diet sodas to water; if anything, doing so may have slightly hurt their health.
What this means for you and your Diet Coke habit
OK, maybe I mean me and my Diet Coke habit. I fully admit to being biased here, but in an educated way. I like my Diet Coke. I’ve also been keeping an eye on research about artificial sweeteners over the years, and while I won’t necessarily defend my soda as health food, nothing has ever convinced me that it’s bad for me. (Sugar-sweetened sodas are a different story; those, we should probably all avoid.)
Now, we have a reasonably large, well-designed, independently-funded study showing that artificially sweetened drinks are possibly better for you than water. I still haven’t seen any news coverage of it, even though a study with the opposite results got coverage a few years back. That study involved 81 women with diabetes in a weight-loss trial, and their HbA1C improved slightly with water compared to diet drinks. Even so, one expert that Everyday Health spoke to about it said that he was “of the opinion that the health risks of diet sodas are overstated.” (Meanwhile, the authors of the most recent study point out that comparing that study to theirs isn’t quite apples-to-apples, since it was a weight loss trial and this one is not.)
That’s an important point to remember about any study on a specific food: they usually apply to a specific medical condition or population. We like to file them away in our mind as “Diet Coke good” or “Diet Coke bad,” but each study only gives us a piece of the puzzle, not a generality. For example this study tells us nothing about Diet Coke’s effects on people who have poorly controlled diabetes, or who don’t have diabetes at all; and it doesn’t say anything about measures other than those related to blood sugar. It didn’t even specifically study Diet Coke, although it’s likely that Diet Coke was one of the more popular beverages participants chose.
To be clear, it is entirely possible that this isn’t a real effect, and and that water and diet drinks are basically equivalent when it comes to your blood glucose and your health. Meyerowitz-Katz says this is probably the most likely explanation, but we can’t rule out the possibility that diet sodas may help glucose control in type 2 diabetes. Maybe they satisfy a sweet tooth and help people avoid other sugary snacks, for example.
The researchers write that their main takeaway is that “maintaining usual [artificially-sweetened beverage] intake may be a tool to continue to help manage T2D if glycemic measures are controlled and stable.” Meyerowitz-Katz agrees: “At worst, there is no difference between diet soft drinks and water when it comes to diabetes control. At best, the diet drinks might be sightly better.”
