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Diet soda helps with weight loss?

You know the moment you learned that your parents were wrong and your face doesn't actually freeze ugly when you make faces at others? Well, I just had a moment like that today. A randomized control trial (RCT, second highest level of evidence btw) from last October stated that non-nutritive sweetened beverages, aka diet sodas actually help with weight loss vs drinking only water. Let me repeat that in a different way, the study reported that diet soda wasn't just neutral, but that it actually promoted better weight loss than just water intake. Double take. Say what? Triple take. This seems a little too good to be true, like when my uncle told me I could get a 100 dollars (doll hairs) for scratching his back; utter garbage. Well thanks to my uncle, I think a little more critically now. Just like my uncle displayed a few red flags, I see two in this study that I'll discuss a couple paragraphs down.


The participants were all pretty similar in health status: they were all within the BMI range of 27-35 and they were between the ages of 18-65. By the end of the study, due to covid and other difficulties, they lost a bunch of people and were down to 262 participants, still a significant number in a RCT. They were randomized into two groups: The "sad" water-only drinkers and the diet soda/water drinkers. The first phase was 12 weeks of assisted weight loss, phase two was 40 weeks of assisted weight maintenance and then 12 weeks of non-assisted weight maintenance. The length of the study is one of the things that makes it noteworthy because it rebukes the doubt that it's just an initial response in the induction phase of the weight loss program, which has been asked in previous short term studies. Throughout the entire study, the diet soda/water group faired better with a weight loss of 1.4 kg more on average than the water-only group. May not seem like a lot but when most nutritionists and providers agree that diet soda makes you fatter, this data creates a stir.


A whole bunch of questions arise when reading this study, like . .uh . . how? My first thought was, well maybe the diet soda curbs the cravings for other treats that are filled with sugar. Then I thought, or maybe the carbonation filled the tummy up more than just straight water so when it came time to eat, the participants ate less. Hmm, not sure about that. My last thought was, maybe the caffeine intake raises the heart rate a smidgen and creates a faster burn, probably not. Either way, the data is decently clear, diet soda not only doesn't cause weight gain but it appears to help. While I'm not as cautious of diet soda as I was a day ago, let's discuss the red flags so that we can understand this study with our eyes wide open.


The first red flag was that this study was funded by one of my favorite organizations (sarcasm), The American Beverage Association, also known as a conglomerate of buddies lobbying government to push more soda and juice down our gullets. When I say buddies, I'm of course talking about Coca Cola, Pepsi and Keurig (Dr. Pepper) et al. They are pretty good at their job by the way, you may have noticed. Pretty soon, sodas and juices will be the beverages of choice over breastmilk, jk, but seriously. My red flag-o-meter always goes off when I see a self-interest group funding a study like this. The study authors make note of the conflict of interest but state that the ABA didn't intervene at all. That might actually be the case but when a scientist wants to keep the bank roll rolling, sometimes results can unintentionally be swayed. We saw this in multiple General Mills funded studies that moved the needle on government nutrition advise. We see the result of that at Disneyland.


The second red flag is that during the study, covid reared its ugly head with all of its social distancing glory; participants no longer met with the study researchers but had to send in photos of foods and diet sodas that they consumed. This reduces the control part of a randomized control trial. I'm not sure if you have ever unintentionally eaten something while at a party and forgotten to log it, but it's a thing. You are probably asking the question, but wouldn't this be a problem for both groups and you would be right, it technically would, but the control part of RCT is really important. It almost undermines an entire study if control is called into question, especially if the the group doing the study is funded by someone that wants the data to go a certain way.


Aside from weight, here is a concern that researchers and gurus have theorized but not proven, as far as I know. Diet soda might cause gut health problems. This is a legitimate concern but as far as I can tell, we do not have any RCT's that I can find that prove it. The idea is that non-nutritive sweeteners kill off good bacteria and cause inflammation giving rise to dysbiosis (imbalance of good and not so good bacteria) and potentially bacterial overgrowth in the small intestine, sounds gross huh. These maladies have been associated heavily with insulin resistance, cardiovascular disease, mental health problems, skin disorder and many other fun harmful things. Again, just theories as far as I know. I know that gut health issues are on the rise, I know that the previously stated diseases are massively on the rise, I know that diet soda consumption is on the rise but unfortunately correlational evidence is super not helpful, especially when social media gets ahold of it.


Here is the deal, one of three things happened in this study. One, the authors falsified information to benefit their wallets per the ABA, two, they unintentionally (incompetently) swayed data toward better results in favor of diet soda or number three, this data is legit and people looking to lose weight shouldn't be afraid of diet soda. My take is that the study is either number 2 or 3 and if it is number 2, the data wouldn't be swayed all that much. An unintentional data error due to bias wouldn't be so much to cause a massive difference. . . . I don't think. Another anecdotal data point to consider is that the most I have asked my patients to do in regards to diet soda is to drink less, I have never completely restricted it. I just tell my patients to not track their diet soda as their water intake and guess what, they still lose weight. So while I recommend not trusting the next uncle that says he will pay for a back scratch, maybe diet sodas are ok during the pursuit of weight loss. Just don't forget about the water intake.

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