Diet Soda: Trick or Treat?

Close your eyes and imagine the crisp sound of a soda can opening.  The fizz awakens and rushes to the surface, each CO2 bubble racing to be the first to exhale into the world, breaking free from the aluminum womb. You can almost feel your dopamine transmitters following suit, effervescing around your pleasure center, and picking up speed as you delicately kiss the lip of the can for that deeply satisfying quench of the first sip.

Quick. What was the can you were sipping? Coke? Or Diet Coke?  Pshaw, you say! Obviously Diet Coke, because we all know that Coke is just liquid calories that contribute to weight gain because your body doesn’t get full from it.  Diet Coke is the greatest! You get (almost) all the taste, without any of the calories! It’s a free lunch! (Heck, it’s a free stay at a knock-off resort in Canada, for that matter!)

Or is it? Hater headlines scream “Diet Coke: the devil’s spawn, and your waist’s worst nightmare!”  “ Not-So-Diet Soda: Tipping your scale!”

Are they right? Or don’t these people have something better to worry about? :(?

Back in the days of the polar bear and his classic Coke, research, and common sense, indicated that frequent consumption of regular soda, at 140 calories a pop, was a huge contributor to weight gain among other issues.  What a great idea, then, to swap them out for similar tasting calorie-free options. But soon, the correlational studies started hitting the newsstands with a surprising result: those who drank the most diet soda now tended to weigh the most.

Drinking diet coke may be just an innocent bystander to the larger culprit behaviors

But you are always lecturing about how correlation doesn’t equal causation. 

Right on! You already know that this type of study is only a reason to delve further, and it is not a causal story.  There could be other things going on here that explain why people who consume large amounts of diet soda weigh more than those who don’t. Perhaps those who are drinking diet soda might also be having it with their fast food. Or maybe those who drink tons of diet soda are less likely to be rehydrating after a kick-ass workout set.  But the relationship was curious enough for researchers to dig deeper.

Should’ve left well enough alone. Diet Sunkist is my savior and natural lip gloss.

Don’t freak out yet.

The first piece of the puzzle that may explain the correlation is a relatively recent discovery that your intestines can taste….


Um, sort of. So in order for glucose (which is one of the ultimate breakdown products of any carbohydrate) to enter our body and get used, a number of things have to happen (insulin getting released is one of them). So when the gut senses or “tastes” glucose at the gates waiting to get into the body, it sends out some messengers to the rest of the body saying, “glucose is here! Here it comes! Get ready to get some energy!”(1) And unless you have an insulin resistance or insulin production problem, the body responds.

OK, that’s sort of creepy and almost mildly interesting. But what does that have to do with my Diet Coke?

When you take human intestinal cells and put them in a little petri dish (studies that are called “in-vitro” studies, meaning in a test tube, not a human body), artificial sweeteners actually cause the gut cells to “taste” glucose just like your tongue does. Theoretically, this would lead your body to “shoot blanks” into your bloodstream, saying “here comes glucose!” but then no energy follows up the announcement. The body would then release insulin in the false hopes of glucose, which could then lower your blood glucose even further, (perhaps by kicking some of the circulating glucose in your blood into muscle cells). This could then theoretically backfire by causing you to be hungrier and eat more.

Can I unread this?! What are you saying to me?!

Wait! Back away from the edge of the bridge. In humans, this has not panned out yet. “In vivo” studies, or studies in real live human bodies, have not found evidence that the gut is tasting the sweeteners, at least when the sweeteners are ingested without any source of calories; the levels of the people’s gut secretions were no higher after having the artificial sweeteners in diet soda than they were after having carbonated water.

There is some research that looked at what happens if you have the artificial sweetener followed by food. One study indicates that while diet soda alone does nothing, if you then follow it up with a meal, you may have higher levels of the gut secretions than if you didn’t have the diet soda to begin with.  Another controlled study, however, found no difference in the secretions or subsequent appetite in people who consumed a meal after either water, sucralose solution, or a sweet glucose drink. So…it’s up in the air, but at this point, the test-tube findings are not played out in real life.

Phew….then I can keep drinking Diet Coke all day long (as long as I never eat after it)?

Probably not good to do either (drink Diet Coke all day long OR not eat–both are lousy choices).  Even though studies haven’t yet shown diet soda alone to actually affect the gut in living human bodies, separating out the calories from the taste of sweet just hints of the “what happens in Vegas stays in Vegas” scam. (Cuz my response to the latter is: maybe…but probably not.) The jury is still out, though, so at this point there is just cause for pause.

I would say keep with the lame, boring mantra that makes dietitians so much less popular than extreme diets or massive macronutrient defamation: “everything in moderation.”  A diet soda here and there is probably fine and will not kill you. But hey, if you can ditch regular diet soda consumption from your life without missing it, go for it.

So then is it better to have the “real thing” instead of diet? 

In this case, if you absolutely must have a soda, I’m actually going to say I think it’s better to go with diet soda than regular until we get more evidence suggesting the contrary.

Oh my gawd, you are so lame. Can’t you just say yes or no? See?! This is why I read L.L. Cool J and Gwyneth’s stuff instead of your blog. They don’t qualify everything they say. They scream their opinions and have published books with strict rules I can follow, and they are so much cooler than you!

Yes, they are cooler than I am. But my guess is that the majority of celebrities’ dietary opinions are not based in science, and while research studies have to be approved by other research scientists to get published, anyone can publish a book. My  suggestion is you make your decisions based on the current research, and leave the celebrities’ gorgeous selves to the entertainment business.

Marily O.


1. The specifics of this are detailed in something called an “incretin” response. Turns out that when you eat glucose, you release more insulin than if you just shot glucose directly into your veins (maybe 50% more!). This is because of the gut cells’ secretions stimulating the insulin release from the pancreas. But the gut secretions are not just promoting insulin, they also signal the body to control appetite essentially by decreasing gut motility, inhibiting gastric emptying, and decreasing food intake.  The gut secretions also have been shown to perhaps play a role in neurogenesis (making new brain cells) and fat metabolism.

Awesome summary of the incretin effect and recent research around it in the article below. It mentions how back in the day (1906) they thought giving diabetics oral doses of intestinal mucosa could solve their problem. It didn’t (because all of these things are degraded once they reach the stomach acid), but now that more is known about the peptides released from the gut there are new and exciting “incretin-based therapies” for Type 2 Diabetics to help control blood glucose and aid weight loss.

Kim, W. & Egan, J.M. (2008). The role of incretins in glucose homeostasis and diabetes treatment. Pharmacological Reviews, 60(4), 470-512.

More Sources:

Latest updates on artificial sweetener and GI tract research (concluding that as of now, real life ingestion of non-nutritive sweeteners does not increase the gut secretions, which are triggered by carbohydrates and fat).

Brown, R.J., & Rother, K.I. (2012). Non-nutritive sweeteners and their role in the gastrointestinal tract. The Journal of Clinical Endocrinology and Metabolism, 97(8), 2597-2605.

Pepino, M.Y., & Bourne, C. (2011). Nonnutritive sweeteners, energy balance and glucose homeostasis. Current Opinions in Clinical Nutrition and Metabolic Care, 14(4), 391-395.


Some eating food post-sweetener studies:

Ford, H.E., Peters, V., Martin, N.M., Sleeth, M.L., Ghatei, M.A., Frost, G.S., & Bloom, S.R. (2011). Effects of oral ingestion of sucralose on gut hormone response and appetite in healthy normal-weight subjects. European Journal of Clinical Nutrition, 65, 508-513.

Brown, R.J.,, Walter, M., Rother, K.I. (2009). Ingestion of diet soda before a glucose load augments glucagon-like peptide-1 secretion. Diabetes Care, 32(12), 2184-2186.

This study describes the epidemiological concern and a subsequent speculation about artificial sweeteners. The authors suggest (but do not present evidence) that the link between artificial sweetener use and weight gain is perhaps the diet sodas are altering taste preferences towards sweeter foods and making fruits and vegetables less exciting. Same authors who did the only study supporting higher gut incretin effects post glucose intake after artificial sweetener preload.

Brown, R.J., Banate, M., Rother, K.I. (2010). Artificial sweeteners: A systematic review of the metabolic effects in youth. International Journal of Pediatric Obesity, 5, 305-312.

A neurological argument supporting the hunches of the speculation in the above paper:

Yang, Q. (2010). Gain weight by “going diet?” Artifical sweeteners and the neurobiology of sugar cravings. Yale Journal of Biological Medicine, 83(2), 101-108.


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