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Is my diet soda really sugar-free? Check its sugar!

April 28, 2015 by Scott Johnson

Sugar-free or sugar-bomb? Sometimes it’s hard to tell!

Living with diabetes, the difference between the Diet Coke we ordered and the regular Coke we’re served isn’t just a few extra calories. It can mean smooth sailing with our blood sugars or a day spent struggling to recover from the mix-up.

Most of the time I can tell the difference between the two, but sometimes the mix is so awful that I just don’t know. Has it ever happened to you? Have you ever had a drink that you suspected might not be diet, but just weren’t sure?

The little things we try

Being a victim of the Diet Coke order gone wrong, a.k.a “The Sugar Bomb,” is a hard lesson to swallow. So I’ve built safety checks into my drink orders, and sometimes they help.

Some examples:

  • I always take a sip of my Diet Coke before pulling away from the drive-thru window (if it’s not diet or if it tastes weird, I still have time to ask them about it).
  • Whenever possible I try to watch the server or attendant fill my drink cup, to make sure it’s positioned under the proper fountain nozzle. This one is hard, though, because perspective and angles can make it really difficult to tell.
  • I annunciate like crazy. “I’d like a large DIIIIIIIIIIIIIIEEEEEEEEEEETTTTTT Coke, please.”
  • And there’s nothing like being at a place where I can fill my own drink. Plus, unlimited refills? Yes, please!

The awkward ask

There are times, though, when it’s not possible to avoid a conversation with the server or employee. I hate being a high-maintenance patron – but not as much as I hate going thirsty or running high blood sugars.

So I politely ask them to double-check and make sure it’s diet. I’ve never had any trouble or pain-in-the-ass attitude from this. If they give me any hesitation, I explain my diabetes and they instantly understand.

Sometimes the new drink tastes completely different, and it’s clear the first one wasn’t diet, and sometimes it tastes exactly the same. In which case, the mix is really bad, or…

It’s the wrong box

There have been four or five times in my life where I’ve filled my own drink cup directly from the fountain machine and I was sure I selected Diet Coke, yet I was also certain that what came out of the nozzle was not diet soda.

How is this possible?

The drink machines we see are only the front side of a complicated system with lots of tubes and hoses. Here’s one behind the scenes example.

Drink station connections

Each flavor choice up front leads to a box of concentrated flavor syrup in the back. They are connected with a hose that delivers the flavored syrup to the nozzle, picking up chilled carbonated water on the way. At the end, assuming all of the settings are correct, we get a delicious beverage!

If you see many flavors up front, you can be sure there is a big thing like this in the back.

Drink station shelving with boxes of post mix flavor syrup

You can see below, there is a labeled hose leading to a labeled box.

I’ve seen a few different organization systems used to try and keep this all straight, but at the end of the day, it all depends on the person changing the empty box.

We are counting on them to put the correct box there and connect the right hose.

Labeled hose leading to a labeled box

Do you see any opportunity for error there? Especially for employees who don’t think there’s much difference between regular soda and diet soda? All it takes is for some sleepy, overworked person to put the wrong box in the wrong place and connect that hose. We’re flying high. Literally.

And that’s exactly what’s happened to me when I’ve noticed in time. After some discussion with the store manager, they go check the connection, and sure enough, it’s connected to a regular soda box.

So how can you really know for sure?

There are three ways I can think of to be sure you don’t get accidentally sugar-bombed by a Diet Coke order gone wrong. 1) Drink water (ok, that’s really healthy, but no fun at all) 2) If possible, get the drink directly from the can or bottle, or 3) Check its sugar!

“What? Check a drink’s sugar?”


Most of the time you can actually do a BG check with the drink to be sure. Ilka and I did checks with a handful of different meters, and here’s what we found.

Note: This will affect your meter averages and reporting (because you’re testing soda, not your blood…). Where possible, I’ll include instructions for marking the test as a “control” reading which will be ignored in your meter statistics, but not all meters allow it. So be aware before you try this.

Accu-Chek Aviva Plus

Coke: 546 mg/dl
Diet Coke: LO (Blood glucose may be lower than the measuring range of the system)
Control: It is possible to mark a reading as a special event by pressing either of the arrow keys, but it is not possible to manually mark a control reading.

Results from testing regular Coke and Diet Coke with an accu-chek Aviva

Bayer Contour

Coke: 106 mg/dl
Diet Coke: LO (test result is below 50 mg/dl)
Control: It is possible to mark a reading as a unique event by pressing either of the arrow keys until a logbook icon appears, then press “M”. It is not possible to manually mark a control reading.

Test results from Bayer Contour check of regular soda

OneTouch UltraMini

Coke: HI (over 600 mg/dl)
Diet Coke: Er 4 (sample improperly applied, or there may be a problem with the meter, or there may be a problem with the strip, or you have high blood glucose and have tested in an environment near the low end of the system’s operating temperature range (43-111°F)).
Control: Insert a test strip, but before applying anything to the strip press ↑ so that ‘CtL’ appears in the upper right corner of the display. Results marked with ‘CtL’ are not stored in the meter’s memory.

Results from the OneTouch UltraMini Cola Test

OneTouch UltraSmart

Coke: HIGH GLUCOSE (You may have a very high blood glucose level, exceeding 600 mg/dL)
Diet Coke: Error 4, Strip Problem (sample improperly applied, or there may be a problem with the strip, or you have high blood glucose and have tested in an environment near the low end of the system’s operating temperature range (43-111°F)).
Control: Insert a test strip, but before applying anything to the strip use ↑ to select “Control Solution” in the display. Marked control solution tests will not be included in averages.

Results from the OneTouch UltraSmart Cola Test


Coke: 212 mg/dL (& control solution icon)
Diet Coke: Er 6 (The test strip has taken too long to generate a signal)
Control: Control solution is automatically detected and a Control Solution icon is displayed.

Results from iBGStar Cola Test

That’s what happened when I tried testing both regular Coke and Diet Coke with the meters I had here. You should give it a try with your meter if you can spare a test strip or two. Unfortunately, I know all too well that we can’t often spare those pricey test strips.

But there’s another way which can be a lot cheaper.

Hello, Diastix!

Before measuring blood sugar we had to measure something that feels kind of gross to talk about alongside Diet Coke…

Box of Bayer's Keto-Diastix for measuring Ketones and Glucose in urine

These test strips are still commercially available over the counter for pretty cheap.

This box, for example, which can be used to measure both ketones and glucose, is listed at Amazon for about $25. Each of these strips can also be cut in half (or smaller) if you really want to pinch pennies.

For a few dollars cheaper, you can get the strips that just measure glucose, which is all you’d need to check your drinks. But I personally think it never hurts to have some ketone strips around.

These strips can be dipped right into your drink, or you can use your straw to put a drop on it, and if your soda is not sugar-free, the glucose testing pad will turn noticeably darker within 30 seconds.

When in doubt, check it out

I hope some of these ideas might help if you’re battling the Diet Coke order gone wrong. Like many things with diabetes, once you have a little bit of know-how and do some detective work you can make an informed decision about what to do.

Unanswered questions

There are some situations where I’m not sure what to do or expect.

What about those things bartenders use? You know, the contraption on the end of a hose that has a bunch of buttons on it for the different flavors? It’s called a Soda gun. Drinks never taste good coming out of those nasty things.

If someone orders a regular Fanta Orange right before I order my Diet Coke, isn’t there residual Fanta Orange in the tube before my Diet Coke comes out? I mean, I can taste the Fanta Orange, yo! How much sugar am I getting?

I bet good bartenders flush the line a little before serving the next drink. But I bet not all bartenders are good bartenders…

And what about those super fancy Coca-Cola Freestyle machines? I really enjoy using them, but I don’t know how they work. I hear they use flavor cartridges, almost like an inkjet printer. But it’s all coming out of the same nozzle, man! Same problem as the nasty bartender drink-dongle! And I also heard that the flavor syrups have sugar…

Ok, ok, ok. I’m starting to overthink things here. Time to have a Diet Coke and relax…

Cheers, Monster Tamers!


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  • Kaki de Maki

    I was a bit surprised by the outcome on the Bayer meter????

  • Hi, Kaki!

    Yes, me too! I expected the Coke to be higher!

  • InternetJunk

    Diet drinks contain a lot artificial flavor and sweeteners Are especially unhealthy for diabetics! I don’t drink soda anymore and I really don’t miss it at all. Also my energy levels went up when I skipped this from my diet. Good luck, you all!

  • Emma Baird

    I’m seriously fussy about diet coke – so I never order it unless it comes in the bottle or can and I can drink it straight from the bottle or can (I always think it tastes flat otherwise), but yeah, mistakenly drinking a full sugar drink is horrible!

  • It definitely has a different feel/flavor depending on where it comes from (tap, bottle, can, etc)! 🙂

    Thanks for reading, Emma!

  • Thanks for stopping by – I appreciate you taking the time to read and share your thoughts. I do feel better when I drink water, and it’s a healthy habit I’m working on. 🙂

  • owenbickford

    Great ideas! I sometimes have to ask restaurants to change the diet soda box/bag because it is expired. The person at the counter usually is quick to respond, but sometimes they are completely unaware that diet drink mix can expire.
    It happens less in very busy places, but there are still occasions where I take a sip of expired soda. It’s almost as bad as expired milk.

  • Mark C.

    I’ve always wondered if I could test something other than blood, but it never springs to mind when I actually have a Coke in front of me. Maybe I’ll remember this the next time my drink tastes off. Great article. I think it’ll be especially helpful to folks who drink “that other brand” since it seems to have an overall sweeter taste to me, even in diet form.

  • The_Analog_Kid

    Thanks so much for the tips. I’ve never really been too concerned with this issue, but obviously, I should be.

  • Tic Jackson

    Wow great idea i have this.problem constantly especially if i am.grabbing drive thru snack as i can’t stop and forgot to be prepared. I constantly argue over flavour of my drink. As i have worked in hospitality and my partner used to manage a fast food restaurant we know our rights as customers and after being served coke twice from the diet button at a drive through i went in and asked to speak to a manager. Itold the manager what was happening and suggested he check the machine. Two boxes of coke and no diet were connect.

    Another problem I have is with places that stock coke zero. Yes it has no sugar but I don’t like the taste. I am used to diet coke and you have it on the menu that is what I would like please and don’t tell me it is whenit isn’t. Geeze I sound horrible. But if you are going to piss on my shoes and call it rain I will not return to your establishment lol. I don’t know about the rest of the world but we have coke life. 25% less sugar and sweetened with stevia. I get told I should drink that as it has less chemicals. Yes and in an ideal world i wouldn’t be diabetic. Hmph.

    Sorry for the rant this is something that grinds my gears everytime i walk out my door.

  • CharlesBDudley

    Anyone know the expected results on a freestyle lite meter?

  • I love your “in an ideal world, I wouldn’t be diabetic” line! 🙂

    Thanks for stopping by, Tic!

  • Thanks for reading, Mark! And yes, I agree! It’s always tough when I’m drinking something I’m not quite used to.

  • Marion Maki

    My sister tasted and asked one time and was told they were out of the “real” Coke so the manager told the employee to hook them both up to diet. Well, she is allergic to aspartame and I’m diabetic, so whichever one they hooked up would have been a problem for one of us! And I’m confused about the Contour strips…high is 106? That would not be a warning to me! Are their results that far off?

  • Oh man! What a catch 22! Not sure about the Contour – I definitely wouldn’t take my at home experiment as a rigorous scientifically valid example. As they say with diabetes – YMMV (Your Mileage May Vary)! 🙂

  • Hi, Charles! We didn’t have a FreeStyle Lite meter on hand, so unfortunately I don’t know… Let us know if you try it!

  • Ewww! That sounds disgusting! 🙂
    Thanks for sharing, Owen!

  • Oh my, Emily! I had no idea… Thanks for sharing!

  • InternetJunk

    Dear Emily,
    Thats exactly what happened to me! Please all here, watch and learn, just skip the coke – COMPLETELY.

    Find some information about aspartame on YT you will be amazed.

  • Mimi

    I always check with a blood meter

  • Tic Jackson

    I have purchased expired diet soft drink from service stations and vending machines before. It does something to my stomach acid and makes me feel ill all day. Stock rotation i thought was promoted in all places apparently has only been important in places i have worked lol

  • Shirley Garrison

    My daughter is diabetic and I am an OVERPROTECTIVE MOM! You are not alone… I’ve often wondered about getting sugary soda from those shared nozzles. We love the new Freestyle Coke machines, because we love the variety of sweet flavors you can add to plain old boring diet coke, but I’ve had my concerns about them, too! There is a little note in the corner of the machine when you fill up that says that the flavors add only about 10 calories to your drink (which {even if it is sugar} it would be less than 3 carbs), but I’m skeptical… because it tastes sooo good! Thanks for the tips for testing with a meter… I’m going to try it!

  • Holly G

    I am trying to figure out an approximate sugar content in my home brewed water kefir using diastix for glucose testing. My original sugar water that I mix before hand has 1 Tbsp sugar per cup of water. The strip stays light blue when I dip it in this mixture. Kefir grains metabolize sugar. After 48 hours of brewing, the strip was light brown/tinge green. After the last part of the brew…72 hours, the strip is completely brown. How can I tell how much of the original sugar is being used up? You said the strip would turn brown if the soda wasn’t diet…meaning there is a high sugar content, but that doesn’t make sense. My full sugar mixture did not change color…the mixture that should have a low sugar content did…Help!

  • Hi, Holly!

    Hmmm… you’ve got me stumped, too. I don’t know anything about the process of brewing kefir grains, or how/when the sugars should be showing up.

    Are you sure the diastix you’re using are able to test glucose and not just ketones?

  • Let us know how it goes, Shirley!

  • Holly G

    They say glucose.

  • Sounds like you’ve got the right ones!

    I’m not sure what to tell ya… as someone living with diabetes, I would trust what the strips are saying as far as how it would affect my blood sugar.

    But again, I’m not familiar with water kefir (though what I’ve read in response to your questions is exactly as you say).

  • Kris Anne Black

    So helpful thank you!

  • Hi, Jackie! Yes, there are charts right on the bottle, usually. You can go look at them at any pharmacy, typically ones at grocery stores even have them out and on display. But if not, I’m sure someone behind the counter would be happy to let you take a look.

    I’m curious if you’ll have similar results to Holly. As you can see from our discussion, she didn’t get the results she was expecting. Keep us posted! Thanks!

  • Hi, Jackie! Any pharmacy usually has them, or can order them. And I see that you’ve already found the discussion with Holly below about water kefir (and the confusing results she got).

  • Jennifer Smith

    I have a freestyle lite and have tried it.. most of the time it works but occasionally I get an error.. but it will read either HI or over 400 for regular and LOW for diet.. I think it might have something do with the temp of the soda too

  • Heri K

    How exactly would this work for fruit juices as well?

  • Hi, Heri!

    Well, it’s not quite the same thing. In the case of diet soda (where there should be no sugar or carb content) versus non-diet soda (where there is sugar or carb content), it can give those of us with diabetes an indication if we’ve been served the wrong beverage. But with fruit juices, I’m assuming you’d like to know how much sugar/carb content there is – and this isn’t an accurate way to measure for that.

  • Mia

    I’ve tested my flavored diet cokes from freestyles in my area, they all come up Lo on my meter (meaning probably sugar free, they don’t seem to spike my BG any either). So that might be something to celebrate!

  • That is awesome news, indeed! Thank you, Mia! My favorite mix so far is Diet Coke with raspberry for most of it, then a little bit of vanilla for the last little bit. Yum! 🙂

  • p j wood

    Some entrepreneur could make a fortune selling strips specially designed to measure sugar content in drinks. It can be risky for us diabetics to take a chance,

  • Calum Smith

    Just tried this as I got the feeling one of the bar staff whilst on holiday in Spain, took a disliking to me. After testing both the drinks he dispensed they were both full sugar. These people just don’t realise the damage they do by providing the wrong drink.

  • Oh my, Calum! That’s awful!

  • Jordan

    FYI the freestyle requires the employee to scan a code on the cartridge before the machine will open. The cartridge is unsweetened and hfcs or aspratame is added by the machine as you pour. The hfcs and diet are loaded in different ways to avoid any mixups.

  • Joe Zuch

    Anyone know what readings a Freestyle Freedom Lite meter will give on sugar and diet sodas?

  • Pat

    I have been using my glucometer to check drinks that are questionable. I got what I think is another sweetened tea from Starbux, it reads 66. So, I used it on some herb tea I made and am sure is sugar free and it reads an 99. is there something in tea that is confusing the glucometer?

  • Pat

    I asked this question and it didn’t post, so I’ll try again. I have had issues with “undisclosed” sugar at Starbux. I talked to them and they promise that if you ask for green tea without any sugar, it will only be green tea. Well, I tested it with my glucometer and got a reading of 60. I figure that was very low so on a hunch I tested a herbal tea that i make that I know has ZERO sugar and it came up at 97ish. Does this method not work with tea? Anyone else see this…

  • disqus_S1ql48Vi9i

    I’ve thought this through as well and so now if I drink one it has to come from a can.

  • Always safe that way!

  • Richard W

    Just had a Tim Hortons Dark Roast, 2 cream, 1 sweetener, at least that is what I ordered. Arrived at my appointment 20 minutes later and checked my BG at that time, over 22.0, Cdn here.. when I went back to my truck, checked the coffee and it was 31.6, glad I only drank half of it,, guess it will be black from now on. my blood stayed over 20 for about 3 hours.

  • Wowza!

  • Sarah Jane

    I had the same experience, so i’m going to go with yes here.

  • Sarah Jane

    I googled and found this article today because this happened to me at work. I’m trying to drink less diet soda and have started drinking tea. I filled up from what I believed to be an unsweetened container, and added 1 packet of sweet and lo to a 44 oz cup of tea. I took a sip and it felt way too sweet. I tested on my meter, and it said 80. I dumped it out.

    I then got some hot water and some earl gray packets and I made my own. To confirm I tested it too. It said 115!

    Tea must have its own kind of sugar here. Never has affected my numbers though.

  • Hi SJ! Great to see you here! That’s absolutely fascinating! Thanks for sharing!

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