Is Pepsi Max bad for your weight?

The Pepsi Max Test

Can artificial sweeteners from diet sodas affect your weight? My six hour experiment the other day implies that the answer might be yes.

The results can be seen above. I drank the Pepsi Max (17 oz.) after about an hour. The black line is the blood sugar and the purple line is the ketones.


Earlier: Planning / Report 1

When the experiment started I was in pronounced ketosis since several weeks (due to a strict LCHF diet). I was fasting six hours before the experiment started.

The first four blood samples were taken before I started drinking Pepsi Max. Blood sugar and ketones were both a bit above 4 mmol/L (which equals a blood sugar of 72 mg/dl). The small variation in the first tests is probably due to the meter not being more exact (normal for home meters).

During the dark mark I drank the Pepsi (50 cl / 17 oz.), it took 10-15 minutes.

Blood glucose results

As you can see nothing special happened to my blood sugar during the experiment. It stayed at around 4,5 mmol/L (80 mg/dl) and the tiny variation is probably within the margin of error of the meter.

Ketone results

If nothing happened to my blood sugar the effect on my ketone levels were more dramatic. As I noted when planning the experiment one of my suspicions were that the artificial sweeteners might trigger a release of insulin. That would lower ketone levels, as ketones are very sensitive to insulin.

Fifteen minutes after drinking the Pepsi my ketone level appeared to drop, from around 4 to 3,4 mmol/L. Then it continued down during two and a half hours until it had dropped by almost 50 percent.

After that the ketone level started rising again. But when I stopped the experiment, almost five hours after drinking the soda, it was still not back where it had started.

What does this mean?

Pepsi Max and other products with artificial sweeteners are thought not to affect peoples weight, as they contain no calories. That’s an oversimplification that ignores any hormonal effects and resulting hunger. If the sweeteners slow your fat burning and increase your hunger they will of course affect your weight – calories or not.

What is clear from the experiment is that something happened. The ketone level dropped precipitously. My interpretation is that this potentially could result in a decreased fat burning, making it harder to lose weight. Perhaps this is due to insulin release, perhaps not.

I wonder: What if your fat burning is impaired for more than five hours, every time you ingest artificial sweeteners?

One objection: Was the culprit the artificial sweeteners or the caffeine in the soda? This experiment can’t tell, but I would gladly bet money on the sweeteners. Perhaps I’ll do a similar experiment later, drinking black coffee instead.

What do you think about the results?

Earlier experiments

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  1. Bjarte Bakke Team Diet Doctor

    Remember that you don't have to give up everything at once. Why not keep drinking the diet pepsi for a little while longer and see you you feel a few weeks from now?

    In my opinion, "giving up" foods/drinks isn't what you do on low-carb. On low-carb you build strong, healthy eating habits, and sometimes you make exception to these habits :) Personally, I have 2-3 beers around two times a month. I know that isn't perfectly healthy, but as long as I do it rarely it's no big deal, for me at least.

  2. 1 comment removed
  3. Kanphong
    If I don't drink it after 5 hours, Will the ketone level rise back to the started number again? and how long time to rise back? I have drunk it 3 times in 6 hours, 10 ounces each.
    Reply: #104
  4. Peter Biörck Team Diet Doctor
    Personally I would not worry to much about that drinking Pepsi Max affects your ketone levels. But I have hard times believing that drinking Pepsi Max several times a day will add anything positive to your health.

    If I don't drink it after 5 hours, Will the ketone level rise back to the started number again? and how long time to rise back? I have drunk it 3 times in 6 hours, 10 ounces each.

  5. John Bedson
    As the blood sugar did not move, you can be certain that there was no insulin reaction provoked by the drink. Therefore no weight gain. The ketones probably reduced because the water in the (very large) drink diluted the blood enough to move the ketone concentration down. Ketones are only a tiny trace element in the blood, so a large drink will have a disproportionately large effect in diluting them.
  6. David
    Diet soda's..ugghhh. Why would anyone bother drinking something like this that tastes like crap and is full of man-made chemicals? I did try diet coke some years ago and put on 5kg in no time. Absolute rubbish.
  7. Mathieu
    I did the test with Coke Zero (more than 1L/33Oz). Measured with my Ketonix, it had no impact.
    Maybe all Diet beverages are not the same.
    Also I did it at lunch where I ate more than usual (LCHF soups), so I was bloated with soups and Coke Zero.
  8. Marcos
    I have a question. Ok, your sugar levels didn't change and your ketones decreased, so I'm not having Pepsi Max on a daily basis.
    But what about having a Pepsi Max instead of a glass of red wine during the weekends? Which one would impact more my weight loss?
    Reply: #109
  9. Peter Biörck Team Diet Doctor
    Hi Marcos!

    Hi Marcos!
    I don't believe anyone have tested this scientifically. But my best guess is that an occasional glass of wine or Pepsi will not significantly impact your weight. :)

    I have a question. Ok, your sugar levels didn't change and your ketones decreased, so I'm not having Pepsi Max on a daily basis.
    But what about having a Pepsi Max instead of a glass of red wine during the weekends? Which one would impact more my weight loss?

    Reply: #110
  10. Marcos
    Thanks for your reply!
  11. Frank
    My god this as bad as the food babe you know the one who said they put nitrogen in the air on airplanes very poor and non scientific.
  12. Helena
    What a pity you can't actually measure insulin at home. I wonder if your insulin level did go up as other studies seem to suggest might happen. Maybe because you are so keto adapted it wasn't enough to affect your blood glucose level but a less keto adapted person might have an insulin response and then a lowering of their glucose as a result of that? Just a thought.
  13. Scott H.
    I lost 15 pounds in 2 months drinking Pepsi Max.
  14. Gracie McGeorge
    Well I'm no scientist but I do know that when I chug a bottle of Pepsi Max or Coke Zero or other diet sodas my tummy is full (even uncomfortable) and thus I am not hungry. Helps cut down on total eating for the day as I do not feel like eating until dinnertime.
  15. Alfonso
    This is very interesting. I wonder though, did you drink the Pepsi without any food all day? If you ingested a LCHF meal and used one bottle of Pepsi to go along with it... would results be the same or would the fat slow the digestion or impact of the Pepsi?
  16. 1 comment removed
  17. Julia
    My thinking is that since ketones are produced when the body requires energy and burns fat to get it that perhaps the amount of caffeine in the sugar-free pop provided enough 'energy' during that short time frame that the body didn't need to find it from its own fat stores. I would recommend that test with a sugar-free / caffeine-free drink... And remember that Pepsi Max has twice the caffeine of other diet pops
  18. nancy
    so could you not just ingest an equal dose of sucralose dissolved in the same quantity of water as a test? this would control for the other chemicals, the carbonation etc and give some clearer results? that would be interesting to do. at any rate, I am convinced that artificial sweeteners cant be good for you period and am phasing them out of my diet.
  19. 1 comment removed
  20. Cathy
    What about Zevia, made from the Stevie plant, all natural, no coloring or anything?
  21. Linda
    I believe your Pepsi Max experiment may have some flaws because it's clear you state the artificial sweeteners did not cause weight gain, but the individual's desire to consume more food in excess of his/her regular meal. There is your weight gain,

    You also stated that if the artificial sweeteners weren't the cause of insulin production, then you surmise it must be the caffeine in the soda, but your next experiment will be coffee. According to Dr. Robert Atkins' Diet Revolution, circa 1972, he clearly states that caffeine consumption should be limited to two cups a day due to its ability to stimulate insulin.

    I don't believe artificial sweeteners cause weight gain, I believe people cause their own weight gain as it is iIlogical to consume a zero calorie additive that results in a caloric result.

    I am not in the medical field. The only proof I have is my own use. I have used artificial sweeteners for over 30 years live a low carb lifestyle. I have not experienced any I'll affects from Splenda (I use Splenda sparingly due to its fillers and that does slow weight loss), sucralose (EZ Sweetz) and Erythirol and neither cause me to overeat.

    Good luck with your caffeine experiment.

  22. John Bueglas
    I drink caffeine free diet Pepsi and there are other sodas that do not contain caffeine. You should repeat the experiment with those.
  23. Pat
    I drink a lot of diet caffeine free pepsi and it has zero effect on my blood ketones and appetite for that matter. That's the only crap I put in my body. Am working on giving it up. I test daily and my readings are pretty consistent running 2.2 - 2.7 mmol/L. My fasting and HbA1C has always been good.
  24. Annika Botes
    What a out toothpaste? It has sweeteners in it. And mouthwater with fluoride, it's horribly sweet!
  25. Evan Armstrong
    There are many tpyes of sweeteners.

    Why doen't you test them all?

  26. TT
    Can you do an experiment with using stevia?
  27. Joe
    Without a baseline this proves nothing really.
  28. Rocky
    Is it possible that it dropped because you drank it fasted. And insulin release is a lot more sensitive?
  29. Flemming
    Based on my experiments (N=1) Pepsi Max Lime has had zero impact on my weight. I've been consuming unhealthy amounts of it during my recent 7 weeks cut and my fat loss has been exactly as predicted beforehand (withno regard for any hypothetical effect of calorie free soda). I'd say it has even aided my fat loss because it curbs my hunger. There are probably other issues with consuming lots of artificial sweeteners but I'll ignore those for now :)
  30. Jodi
    This is interesting. I sound a lot like this. I have been on a low carb, almost zero carb diet for 4 weeks. It seems, if i have any carbs, my ketone levels drop to zero. I usually have 2 eggs for breakfast, bone broth for lunch, and meat, cheese and a green vegetable for dinner. I am not hungry through the day and I am barely losing any weight. I am drinking a lot of caffeine free diet Pepsi, and my ketones barely register.
  31. 1 comment removed
  32. Elaine
    I want you to do the same thing with black coffee since it is promoted to drink during fasting, but it can mess with cortisol levels which must impact blood sugar, insulin, ketones, etc.?
  33. Gerhard Wessels
    I was in day 2 of a water fast and drank about a liter of Pepsi Max throughout a day of swimming laps in a pool and not ingesting anything else except black coffee and water. Imagine my surprise when I gained 1kg by the next morning.. I saw the same from 7UP zero. Cola cola zero does not have the same effect, I have lost 28kg drinking liters of it.. saw the same results on my wife, half a kg down when she doesn't drink it and one kg up when she does. I stopped buying it entirely now and suggested everyone I know to do the same.
  34. Nitaant Singh
    the 1kg/1/2kg up down is due to water weight, your not going to gain 1kg of fat (a 9 x 1000 = 9000 calorie surplus) from even 10 litres of pepsi max in one day.

    To address the experiment, ketone production is a byproduct of being in ketosis, not the reason for it. Your body will stay in ketosis to keep using ketones for fuel as long as there is no glucose available. Your ketone blood levels mean nothing to being in ketosis or to fat loss. They are not the reason for it, higher ketone blood levels do not mean more fat loss.

  35. Vicky
    I drank 2 liters of Pepsi max a day for 2 weeks but I have now stopped. Will this effect my weight loss and health ? I have stopped completely now.
  36. sami
    Do you have a youtube channel. I would watch you pull apart interesting studies.
    Reply: #137
  37. Crystal Pullen Team Diet Doctor

    Do you have a youtube channel. I would watch you pull apart interesting studies.

    Here is a link to our YouTube channel

  38. Jay
    I don't think that a sample size of one makes for either reliable or accurate data
  39. Jeff
    Can confirm the same with artificially flavored whey protein. Between the two, i’d rather cut out artificially sweetened soda.
  40. Cass
    Nice try, but stay in school a bit longer if you want to go the science route 😉
  41. common sense

    I think we need another test run with carbonated water.
    Maybe it's not the caffeine?
    Maybe it's not the artificial sweetener?
    but possibly the carbonation?
    Does carbonation affect ketones?

    No, otherwise breathing would make you fat (ignoring the obvious reason why breathing technically does).

  42. Kaspars B
    I've been on a low carb diet for about 4 months and I'm downing about 5 cans of Pepsi Max a day. A lot of walks and sessions on the exercise bike.

    Now I'm not saying that drinking diet sodas is necessarily healthy but I've lost about 37 pounds so I don't think it has that much of an effect on ketone levels. At least not for everyone.

  43. Raymond
    Might not be the artificial sweeteners causing the problem as much as the caffeine.
    When I did the Atkins diet some years back there was a special mention in the book concerning coffee intake and how it can upset ketosis. I drank caffeine-free diet Pepsi or caffeine-free diet Coke with no problems
  44. Mansoor Mullan

    I’m with Raymond on this one. Since teenage years I had a problem with drinking too much caffeine based drinks.

    Once I developed diabetes I dropped the sugar based versions for diet/sweetener based alternatives. I’ve always had a problem keeping my weight down but wouldn’t say that I was grossly overweight.

    Recently I tried for a few weeks to restrict my intake of these diet caffeine drinks especially before bedtime. Low and behold I lost weight and as a side note my sleep improved as well as overall general health.

    For me i believe it was the effect of caffeine.

    Incidentally lowering sweetener intake improved concentration levels so I think the combination of caffeine and sweetener is a very detrimental one.

  45. Kellie
    I think the caffeine is addictive
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