Diet soda, Twinkies, and the Questions that Matter

Episode Summary: In this episode, I look at diet soda, artificial sweeteners, and the real-world question that matters most: compared with what, at what dose, for whom, and at what tradeoff?

Diet Coke, Twinkies, and the Questions That Matter

I start with a memory from medical training: a cardiology professor walking around with a Diet Coke in one hand and a Twinkie in his pocket. Was he making a smart tradeoff, or fooling himself? That image captures the artificial sweetener debate well. A diet soda may be a useful substitute if it replaces a sugary drink, but it becomes less compelling if it simply gives us permission to eat more ultra-processed foods.

The cleanest case for artificial sweeteners is substitution. In the CHOICE trial, adults who replaced caloric beverages with water or diet drinks lost a modest amount of weight over six months, suggesting that noncaloric beverages can help when they replace sugar-sweetened drinks.  The SWITCH trial similarly found that people assigned to non-nutritive sweetened beverages did at least as well as those assigned to water after a 52-week weight management program. 

I also explore the common fears around artificial sweeteners. The cancer concern has roots in older animal studies involving very high doses, but the National Cancer Institute notes that the saccharin bladder cancer mechanism seen in rats does not apply to humans, and saccharin was removed from the U.S. carcinogen list in 2000.  A large French observational study, NutriNet-Santé, did find a small association between artificial sweetener intake and cancer risk, especially aspartame and acesulfame-K, but observational studies can’t prove causation and are vulnerable to residual confounding. 

On weight gain and glucose metabolism, the evidence is less alarming than the headlines. Randomized trials do not support the idea that diet soda inevitably causes weight gain. And in the SODAS trial, replacing artificially sweetened beverages with water in adults with type 2 diabetes did not improve glycemic measures, which weakens the claim that diet drinks secretly worsen blood sugar control. 

The microbiome question is interesting but not settled. A well-known 2014 study suggested artificial sweeteners could alter the gut microbiome and glucose tolerance, but much of that evidence came from mice and a very small human experiment.  More recently, the SWEET study found that sweeteners and sweetness enhancers, when used within a healthy diet, supported weight-loss maintenance and were linked with beneficial gut microbiome shifts in adults with overweight or obesity. 

The real issue may not be whether Diet Coke is “good” or “bad.” Water wins the purity contest. But food and drink also provide pleasure, ritual, and sustainability. If a diet soda helps someone avoid sugar and enjoy lunch, that may be a reasonable bargain. But if it becomes a permission slip for a daily Twinkie, we should pay attention. Ultra-processed foods matter because in a controlled feeding study, people ate about 500 more calories per day when eating an ultra-processed diet. 

Takeaways

Ask the better question: not “Is diet soda good or bad?” but “Compared with what, at what dose, for whom, and at what tradeoff?”

Artificial sweeteners appear most useful when they replace sugar-sweetened drinks, and less useful when they replace water.

Diet soda may be a reasonable pleasure for many people, but it is worth noticing whether it helps reduce sugar—or simply makes the Twinkie in your pocket easier to justify.

Transcript

Diet Soda And The Twinkie Test

SPEAKER_00 0:02

I like diet soda. Part of me thinks, why waste calories on regular soda if I'm perfectly happy with the diet version? Sounds like a pretty good trade. Most of the pleasure, none of the sugar. But then I remember my cardiology professor walking around with a diet coke in one hand and a Twinkie in his pocket. Was he on to something? Or was he misguided? Let's find out. Hi, I'm Dr. Bobby Du Bois, and welcome to Live Long and Well, a podcast where we will talk about what you can do to live as long as possible and with as much energy and figure that you wish. Together we will explore what practical and evidence-supported steps you can take. Come join me on this very important journey, and I hope that you feel empowered along the way. I'm a physician, Iron Man triathlete, and have published several hundred scientific studies. I'm honored to be your guide. Welcome, End of One Nation, and my dear listeners, to episode number 71. Diet Coke, Twinkies, and the Questions That Matter compared to what and at what trade-off. When I was in my medical training, one of my cardiology professors had a habit I never forgot. He'd walk around with a Diet Coke in one hand and a Twinkie in his pocket. He was a really smart cardiologist and a bit overweight. At the time I remember thinking, is this really the nutritional strategy of a heart expert? On the one hand, maybe he was being perfectly rational. If he wanted something cold and fizzy, caffeinated and sweet, the Diet Coke spared him the sugar and calories of a regular Coke. Maybe this was harm reduction. Enjoy the Twinkie if you must, but at least don't wash it down with another 150 calories of liquid sugar. But there were other possibilities. What if the Diet Coke was not innocent? What if the artificial sweetener was doing harm on its own? Increasing your cancer risk, altering metabolism, changing the microbiome, or driving cravings. And what if the Diet Coke made the Twinkie easier to justify? That memory stayed with me, partly because I understand the logic. I enjoy diet sodas too, often in the afternoon when I'm thinking about a snack. My thoughts go like this. If I like the diet version, why spend the calories on the regular one? Why waste sugar and calories on a soda when I can save those calories for something I enjoy more, like yummy peanut butter or a brownie? So I'm not a completely unbiased observer. I'm motivated by that old memory of my professor and by my own habits. I want to know whether the bargain makes sense. Is a diet soda a smart trade-off? Is it a harmless pleasure? Is it a metabolic trick? Or is it a permission slip for Twinkies? Then there's the Twinkie itself, a symbol of ultra-processed food. Was one Twinkie a day really so terrible? Or was it just a clue to a bigger problem? That image, diet coke in one hand twinkie in the pocket, is the artificial sweetener debate in miniature. Was my professor onto something? And when I choose

Compared To What Trade Off

SPEAKER_00 4:18

the diet soda, am I? To figure this out, there are critical questions. Compared to what? And at what trade-off? Compared with a regular Coke, diet coke may look like a win. Compared with water, maybe less so. What if we compare three options? A Diet Coke plus a Twinkie, regular Coke plus a Twinkie, or water plus some fruit. Now the story gets more complicated. And that second question at what trade-off is important? In a perfect world, we would get all the benefits with no downside. Sweetness, fizz, caffeine, with no sugar, no calories, no cancer concern, no microbiome concern, no appetite effect, and no permission slip for the Twinkie. Wouldn't that be great? Well, diet soda tempts us with that promise. Maybe it really is close to that for many people. Most of the pleasure of soda, almost none of the sugar calories. But maybe the bargain isn't completely free. So let's keep coming back to the questions compared to what and at what trade-off.

The Best Case For Substitution

SPEAKER_00 5:42

Part one, the simplest case for artificial sweeteners. Well, before diving in, let's set the stage. Non-sugar sweeteners are really common. Half of Americans consume some each day, although about 30% don't use them at all. The most common ones are Splenda or Sucralose, Sweetenlow, or Saccharin, Equal, or Aspartame and Stevia. I call them non-sugar sweeteners as they aren't all artificial. Stevia is a natural sweetener. But today I'll call them non-sugar sweeteners or artificial sweeteners to have kind of a general term. These non-sugar sweeteners really work. They're super sweet, perhaps 200 to 600 times more sweetness than sugar. And they're in many foods and drinks. Here's the simplest and perhaps best case for non-sugar sweeteners. Substitution. If someone is drinking calories, a regular Coke or a sugar sweetened juice, and they replace those calories with a non-caloric beverage they still enjoy, that may reduce enough calories to matter. One important study here is the choice trial. Choose healthy options consciously every day. This study randomized 318 adults who were overweight or obese. Participants were randomized to several groups. In the first one, they replaced sugary beverages with water. The second group replaced sugary beverages with diet ones. Over six months, both groups lost about 2% of body weight. Not a dramatic result. But replacing caloric beverages with non-caloric ones produced modest weight loss. That's the cleanest case for diet soda. Fewer calories, a bit more weight loss. Now, the study doesn't show that diet soda is good for you or that diet soda makes you thin. But if the alternative is a sugary drink, a diet drink may be a useful swap. So if my professor's diet coke replaced a regular Coke, this study points in his favor. He wasn't making a perfect choice, but he may have been making a better one. And this is the theme that will run through the whole episode. Artificial sweeteners look best when they replace sugar. They look weaker when they replace water. And they look most suspicious when they become a permission slip for that twinkie. That's the best case for diet sodas or non-sugar sweeteners.

Cancer Fear And Weight Paradox

SPEAKER_00 8:42

But now we need to explore the issues that folks say are really bad. Part two, the myths. Myth one, artificial sweeteners cause cancer. Let's start with the scariest claim. Artificial sweeteners cause cancer. Now, this myth didn't come from nowhere. The first major danger signal was not a spartane, it was cyclamates and saccharin. In the late 1960s and 70s, animal studies linked those sweeteners with bladder cancer in male rats. Based upon information like this, cyclomates were banned in the United States in 1969, and for a while, saccharin was put on a cancer list. This began the cancer fear. But like most health issues, it's more nuanced. Dose and biology matter. Those early rat studies exposed the animals to massive doses of these sweeteners. One author estimated the exposure was roughly equivalent to hundreds of diet sodas per day. And with saccharine, the National Cancer Institute later noted that although high dose saccharin was linked with bladder cancer in rats, that mechanism didn't apply to humans. And saccharin was removed from the U.S. carcinogen list in 2000. The modern cancer concern is more subtle. A big human study you might hear about is Nutranet Sante, a French observational cohort. It included over 100,000 adults and found that those people who consumed more artificial sweeteners had a slightly higher overall cancer risk compared with those who didn't consume them, with a hazard ratio of 1.13 or potentially a 13% increase in cancer risk. Now, what should we make of this study? The study was observational, meaning they didn't randomize folks to either drink or not drink artificially sweetened beverages. Rather, they just asked what folks ate and drank, and then observed what happened to them. And it's very possible that people who use more artificial sweeteners differ from people who don't in body weight, diet behavior, diabetes risk, medical surveillance, smoking alcohol, and many other ways. Now, the authors tried to adjust for many factors, but residual confounding is hard to eliminate. I conclude from most observational studies that the findings may be interesting, but absolutely not definitive. So the cancer myth has an origin with the rat studies, and then a potential signal from an observational study. My practical verdict, I understand the cancer concern, but don't think that having a couple of sodas a day will be the cause for me. A whole lot of other factors are likely way more important. Myth two, diet soda makes you gain weight. Now, the next myth is the diet soda paradox. Ping pull drink diet soda to avoid calories, but somehow they end up heavier. This myth came largely from observational studies, where diet soda drinkers often looked metabolically worse. They were heavier, had more diabetes, or gained more weight over time. But here's the evidence problem. People often switch to diet soda because they're already gaining weight or already worried about diabetes. That is reverse causation. If someone is told your glucose is high, lose weight, stop drinking regular soda, and then you switch to diet soda, you can't blame what happens on that soda. The diet soda may simply mark someone who is already at higher risk. That's why randomized trials matter. I mentioned the choice trial, where folks were randomized to drink diet beverages and lost weight. Another useful study is the switch trial, where 500 folks who were overweight or obese were randomized to either drink water or non-calorie sweeteners. They also were given general weight loss guidance. Here's what happened. At 52 weeks, the water group lost about 13 pounds, while the diet beverage group lost 16.5 pounds, a difference of about three pounds. The effect was modest, but if diet drinks inevitably cause weight gain, that's not the result you'd expect. So the verdict is not that diet soda is a great weight loss drug. But it seems pretty clear to me from the evidence that diet soda doesn't seem to cause weight gain.

Glucose Control Cravings And Microbes

SPEAKER_00 14:17

Myth three, diet soda ruins our glucose metabolism. Another argument is that artificial sweeteners may mess with our metabolism, our insulin levels, our glucose tolerance, and our risk of diabetes. This is biologically plausible. Sweet taste isn't just a flavor, it's part of a system involving the gut, the brain, hormones, and reward. But again, we need to move from a cool theory to some real evidence. The SODAS trial. Now, you gotta love the researchers for inventing fun names. And this one is the study of drinks with artificial sweeteners. The SODAS trial randomized 181 adults with type 2 diabetes who regularly consumed artificially sweetened beverages. One group continued drinking 24 ounces per day of those drinks. The other replaced that amount with plain water, still or sparkling, for 24 weeks. The trial found no evidence that substituting water improved glycemic-related clinical care measures. Or conversely, those who drank the diet drinks didn't have bad changes in their blood sugar. This is a nice myth busting study because it tests a very concrete claim. If diet beverages are secretly worsening glucose control, then replacing them with water should help. In sodas, it didn't. Now, that doesn't say Diet Coke is better than water or that all of us should drink diet soda, but it weakens the claim or debunks the myth that artificially sweetened beverages are metabolically harmful. With all the great names for these trials, I am still waiting for the Twinkie trial. So my practical verdict, the glucose metabolism concern is plausible, but the SODAS trial doesn't support the idea that replacing diet drinks with water improves glycemic control. So I don't think the myth is true that artificial sweeteners hurt our glucose control. And now for myth four. Diet soda tricks your brain and makes you eat cookies. Now, this is a pretty reasonable sounding myth. Sweet foods usually have a bunch of calories. Artificial sweeteners break that signal. So maybe the brain says, nice try. Now go find the real sugar. This is exactly why my professor's Twinkie matters. Perhaps, perhaps the diet code caused him to want the Twinkie. What's the evidence for this? There are animal studies suggesting that separating sweet taste from calories can affect appetite, reward, and metabolic signaling. And some people could experience diet soda this way. They drink the diet soda, it doesn't satisfy the sugar craving, and they go looking for that twinkie, cookie, brownie, or other sweet foods. Hmm. If this compensation effect were real for most people, then the beverage substitution trial should have failed. People would simply eat back the calories. But that isn't what we generally see. In the choice trial, replacing caloric with non-caloric beverages produced modest weight loss. In the switch trial, 500 folks assigned to artificially sweetened beverages did at least as well as the water group and actually maintained slightly more weight loss at 52 weeks. So the simple story, diet soda makes you eat cookies, is too strong. The better story is it likely depends on the per person and the purpose. Diet Coke is not the same psychological intervention for everyone. For one person, it's a tasty, cold, caffeinated beverage. Now, that person wants fizz, caffeine, and a ritual with lunch. In that case, Diet Coke may be a good substitute for regular Coke. For another person, it is an attempted substitute for dessert. They want the combination of sweetness and calories. In that case, Diet Coke may not scratch the itch. So the question isn't did Diet Coke cause me to eat the Twinkie? The better question is, did Diet Coke help my cardiology professor justify the Twinkie? My practical verdict. Diet sodas don't mean we're doomed to eat more Twinkies. The clinical trials don't support that for most people, but you can test this in yourself and find out. And now we get to myth five. Artificial sweeteners wreck the microbiome. This myth and concern is a pretty new one against artificial sweeteners. The idea is that these sweeteners may not contain calories, but these non-sugar sweeteners may still alter the gut microbiome. And those microbial changes may affect glucose tolerance or metabolic health. About 10 years ago, a study launched the buzz around this topic, which was titled Artificial Sweeteners Induce Glucose Intolerance by Altering the Gut Microbiota. But it's important to look closely at the study. The noteworthy findings were primarily in mice. The paper did include some observational human data and a tiny study in people. Just seven healthy volunteers. For that part of the study, the investigators found folks who didn't normally consume artificial sweeteners and gave them hidosaccharin for a week. Four of the seven showed microbiome changes and worsened glycemic responses. Interesting, yes. An evidence-based verdict, definitely not. A mouse study plus a seven person human experiment is hypothesis generating. It tells us this mechanism is possible and worth studying. It doesn't tell us that ordinary diet soda use wrecks the human gut. And to make the microbiome myth less likely, there is the SWET study. SWEET stands for sweeteners and sweetness enhancers impact on health, obesity, safety, and sustainability. I'm not quite sure how they make that acronym work. Anyhow, the SWET trial included 341 overweight or obese adults. All of them were given a general healthy weight loss diet. Half of them use non sugar sweeteners. The other half did not. Both groups lost weight. Here it gets interesting. The non-sugar sweetener group did have changes in their microbiomes. But the changes identified were felt to be beneficial ones, not shifts to harmful bacteria. Now, although the earlier study with mice and seven humans showed some microbiome changes viewed as problematic, the sweet trial had 50 times more people in it and found no bad microbiome changes. So, do nonsugar sweeteners affect the microbiome? Perhaps, and perhaps in ways that aren't bad for you. Like lots of things that change the microbiome. Fiber changes the microbiome. Exercise changes the microbiome. My practical verdict, I don't think that the evidence supports this myth. Non-sugar sweeteners may not be microbiome neutral, but they don't seem to be problematic.

Joy Sustainability And The Real Risk

SPEAKER_00 23:06

And now to part three. The joys of a trinkie or other sweet foods. Now we get to the part of the episode that I think matters most in real life. If the goal is purity, drink water. Water wins. It has no sugar, no sweetener, no additive, no calories, no controversy. But food and drink are not just nourishment. They provide joy and ritual and social connection in our lives. A cold diet soda with lunch may give someone real enjoyment, that plain water simply doesn't. That definitely doesn't make it a health food, but enjoyment matters. A joyless diet that you or I abandon is not better than a pretty good diet that we can sustain. Look, in a perfect world, you'd get the benefits with no downside. Diet soda may not be perfect. You might still have reasonable questions about appetite, microbiome effects, and long-term observational signals. But compared with regular soda, it may be close enough for many people. Much of the pleasure, far fewer calories, much less sugar. So maybe the right question is not, is Diet Coke better than water in a purity contest? The better question is, does Diet Coke give me enough pleasure and sugar reduction to justify any plausible downside? For many people, the answer may be yes. The perfect beverage you resent may be less useful than the pretty good beverage that helps you avoid sugar and still enjoy lunch. But now we have to come back to the twinkie. I've done a whole episode on ultra-processed food, so I won't redo that here. But the twinkie matters because it reminds us not to stare so hard at the Diet Coke that we miss that Twinkie in the pocket. A Twinkie is an ultra-processed food. That doesn't mean one Twinkie is poison. But ultra-processed food patterns can make overeating easier. In my ultra-processed food episode, I discussed a key study, small but really important. When folks were randomized to a diet with or without ultra-processed food, they ate 500 calories per day more when they had ultra-processed food and gained weight. So a Twinkie day may not be catastrophic, but if the Diet Coke makes the Twinkie become a regular part of your day, then we need to be careful. Let's wrap up. Was my professor wise or misguided? Well, maybe a little of both. Wise if the Diet Coke replaced a regular Coke. Misguided if he felt that lots of Twinkies were fine. And when I reach for a diet soda myself, the same rule applies. If it gives me pleasure and helps me avoid sugar, maybe that's a good bargain. If it becomes a permission slip for more desserts, maybe not. So where do I land? Honestly, somewhere in the middle. I don't think artificial sweeteners are poison. In nutrition, the right question is rarely is this one thing good or bad. The better question is compared with what? And at what dose, for whom, and at what trade-off. I'll still enjoy Diet Coke, but I will also see if I often have a twinkie hiding in my pocket. Please let me know what you do in your life. Do you enjoy diet drinks? Are you fearful of their consequences? Send me a note through the podcast website or at uh Bobby at drbobbyevidence.com. Thanks so much for listening to Live Long and Well with Dr. Bobby. If you like this episode, please provide a review on Apple or Spotify or wherever you listen. If you want to continue this journey or want to receive my newsletter on practical and scientific ways to improve your health and longevity, please visit me at Dr. Bobby Livelongandwell.com. That's doctor as a dr bobby livelongandwell.com.