Diet Fasting

Does Acesulfame K Spike Insulin?

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If you’re following a low-carb diet, or a diet with low-carb periods, like Carb Backloading or Intermittent Fasting, then you probably drink diet sodas. They’re a convenient, tasty alternative to water, coffee, and tea. And, more importantly, you can enjoy the sweet taste without worrying about the insulin spike that you’d get from a sugary drink. Or can you?

If you’ve done research on Carb Backloading, then you’ll be aware that Acesulfame K (Ace K) is forbidden because it spikes insulin. But does it really?

Don’t even think about drinking it, you might get fat. – (c)


We love Kiefer, so let’s take a quote from part of an interview series with Sean Hyson:

Sean: Going back to sweeteners, you make a point in the book about acesulfame potassium raising insulin levels. I noticed that Coke Zero has a small amount of it, but not Diet Coke. Based on that, would you say that Coke Zero could therefore possibly spike insulin and is a bad diet soda choice?

Kiefer: Yeah, I would go with the Diet Coke. Acesulfame potassium definitely causes an insulin response. So many factors can influence that so it’s hard to say how intense it is. I have noticed that people who drink a lot of energy drinks that have acesulfame potassium don’t fare nearly as well on Carb Nite until they cut those out. So I would say that the response is significant, even with a small amount.

In his Carb Backloading book, Kiefer references three studies. The first study found that infusions of Acesulfame K increased insulin secretion in rats [1]. The second part of that study examined the effects of Acesulfame K on isolated rat pancreatic islets [2]. It found that Acesulfame K had a dose and glucose-dependent effect on insulin secretion; but, most importantly, even without glucose it promoted insulin secretion. The third study found that artificial sweeteners with a bitter taste (including, but not limited to, Acesulfame K) augmented the insulin response from isolated rat pancreatic islets in the presence of glucose.

That appears to be strong evidence that you should avoid Acesulfame K. If you’re a rat.

Are You A Rat?

Don’t let him near your Red Bull Sugarfee! – (c)

Let’s look at the first study:

Injection of Acesulfame K (150 mg/kg body weight) increased the plasma insulin concentration at 5 min from 27.3 +/- 3.0 microU/ml to 58.6 +/- 4.2 microU/ml without any significant change in the blood glucose. Infusion of Acesulfame K (20 mg/kg body weight/min) for one hour maintained the insulin concentration at a high level (about 85-100 microU/ml) during this period, and at the same time blood glucose was gradually reduced from 103.0 +/- 7.3 to 72.0 +/- 7.2 mg/dl. When using different amounts of Acesulfame K, the insulin secretion was stimulated in a dose-dependent fashion.

The human equivalent dose is calculated as follows:

Human equivalent dose (mg/kg) = rat dose (mg/kg) x human Km/rat Km

which gives, for adult humans,

Human equivalent dose (mg/kg) = 150mg/kg x 6/37 ~ 24mg/kg.

In particular,  the equivalent dose for a 60kg adult human would be 1440mg. But how much diet soda would you have to consume to achieve that? Let’s make a reasonable estimate using the following information:

The ADI for acesulfame K is 15 mg/kg body weight per day for children and adults. This means that a 150 pound person can safely consume about 25 12-fluid ounce cans of diet soft drinks sweetened with a typical blend of acesulfame K and aspartame, or 20 tabletop sweetener packets nearly every day over his or her lifetime without any adverse health effect. The typical amount of acesulfame K in a 12 fl ounce beverage using an acesulfame K-aspartame blend is 40 mg; the average amount per sweetener packet is 50 mg.

Assume therefore that for every litre of diet soda there is approximately 140mg of Acesulfame K. That means that you’d have to consume 10 litres of diet soda to produce an insulin response equivalent to the one in the study. But even that might not be true, since the Acesulfame K was infused. We don’t know if it would have the same effect when taken orally. If you can imagine a 60kg person drinking 10 litres in one sitting, then perhaps this study is useful, but otherwise it seems slightly ridiculous!

What About Human Studies?

A review article [4] found that:

However, data from numerous publications on the effects of low-energy sweeteners on appetite, insulin and glucose levels, food intake and body weight have shown that there is no consistent evidence that low-energy sweeteners increase appetite or subsequent food intake, cause insulin release or affect blood pressure in normal subjects. Thus, the data from extensive in vivo studies in human subjects show that low-energy sweeteners do not have any of the adverse effects predicted byin vitro, in situ or knockout studies in animals.

And according to a study [5] investigating the effects of artificial sweeteners on glucagon-like peptide (GLP)-1 in humans:

The metabolic consequences of increased GLP-1 release after ingestion of both artificial sweeteners and glucose remain uncertain. In the present study, no significant differences were observed in either plasma glucose or insulin after diet soda versus carbonated water ingestion, despite the significant differences in GLP-1.

Therefore it seems doubtful that Acesulfame K produces an insulin response, and especially not without carbohydrates!


If you enjoy drinking diet sodas then you shouldn’t worry about it. If your goal is fat loss, then you will not derail your progress by including them.


Kiefer responded directly to the article recently, here are his thoughts:

I made the point distinctly in the book and in interviews that it’s not something to worry about unless things seem off. The direct studies on Ace-K (particularly on ketogenic diets in humans) is pretty much non-existent. There’s evidence to show it can increase insulin release and can shift the time-peak of insulin release in the presence of glucose, which may also happen with any insulinotropic substance (leucine, possibly ketones). So, it’s a possible culprit when things go wrong. To spend so much time on such minutiae when there’s not enough research to answer the question under the conditions being considered is akin to a religious debate that no one can win. I’m sticking with the fact that ace-k has been shown to cause cells of the pancreas to release insulin and the observation of hundreds of clients who, when having trouble, strip sugar-free sodas amazingly no longer have problems. Also, worth pointing out, for those with appreciable amounts of muscle, I’ve never seen sugar-free beverages have any effect whatsoever… it’s only “normal” people who seem to have an issue or, actually, stage athletes as they reach the insanely low levels of body fat.

(See this post in the Dangerously Hardcore Facebook group.)

So, in my summation: don’t worry about it unless stuff starts going wrong, then realize it’s a possible source of trouble.

There you have it. If you’re making progress, don’t worry about diet sodas. If you’re not, consider the possibility that you might have to remove them.

Thanks, Kiefer!


[1] “The effect of artificial sweetener on insulin secretion. 1. The effect of acesulfame K on insulin secretion in the rat (studies in vivo).”

[2] “The effect of artificial sweetener on insulin secretion. II. Stimulation of insulin release from isolated rat islets by Acesulfame K (in vitro experiments).”

[3] “Effects of artificial sweeteners on insulin release and cationic fluxes in rat pancreatic islets.”

[4] “Sweet-taste receptors, low-energy sweeteners, glucose absorption and insulin release”

[5] “Ingestion of Diet Soda Before a Glucose Load Augments Glucagon-Like Peptide-1 Secretion”

12 replies on “Does Acesulfame K Spike Insulin?”

Great article man! Finally some human studies around here. I’m tired of all these rats publications serving as basis for human metabolism. Just one quick question. Is it the same with aspartame since it is metabolized into amino acids? Does that sweetener cause an insulin response?

Craggsy said:
Great article man! Finally some human studies around here. I’m tired of all these rats publications serving as basis for human metabolism. Just one quick question. Is it the same with aspartame since it is metabolized into amino acids? Does that sweetener cause an insulin response?

Thanks, Mike! There is no evidence that aspartame causes an insulin response in humans.

Nice article here. However, the argument remains, especially for diabetic and pre-diabetic people: There is a lot of evidence that suggests that diet sodas aren’t good for you. However, there is also a load more evidence that states regular, sugared sodas are way worse for the pre-diabetic and diabetic community. If I were diabetic, I would most certainly choose a diet soda over a sugared one. Therefore, I suppose the moral of the story is that mostly everyone should limit the intake of all types of sodas, as they really have very little benefit nutritionally or otherwise.

In the past 6 months, my A1C levels have gone up almost 2%. I have Type 2 diabetes, but my levels have never been too bad. The doctor upped my Metformin dosage. My levels did not go down. They went even higher. This time the doctor told me I was going to have to start testing my sugar levels daily. This is when I figured out the one change in my diet over the passed few months. I drink a lot of water, but I like to flavor it. I had been using Crystal Light Liquids which contains Acesulfame K. Since I have stopped using the flavoring, my sugar has been going back to normal levels. I fully expect my next A1C check to be back to what it was. I also want to thank you. I could not figure out what the difference between Diet Coke and Coke Zero was. I only drink Coke Zero when we go to the movies…no more…Thank you!

That’s interesting, so you attribute stopping the Crystal Light to reducing your blood sugar levels? How do you think it was elevating your blood sugar?

After some experimenting I found that my blood sugar levels were lower when I did not drink the Crystal Light. I stopped drinking it and my blood sugars have made a significant improvement. I wondered why my sugar was up on the days we went to the movies. I had stopped drinking sugary sodas at the movies and had basically switched to Coke Zero. Now I am checking what sweeteners are used before buying something to drink. Next month will be my quarterly A1c test. If my blood sugar has dropped…I have found the problem and will let you know.

When I went to my doctor last month. My A1c level had dropped over 1 point. I still believe it has to do with Acesulfame K. It is not just Crystal light that has the Ace K chemical. There are several diet drinks or low sugar drinks that have it. There are foods that have it too. If I am trying something new. I read the labels. Different chemicals effect different people. Cutting this one out of my diet, has definitely helped.

Marie- I have a low carb dr, and I have pre-diabetes, so am on a low carb diet, and the diet my dr. gave me speficially seaid no ace K, so I totally agree with you that it can spike insulin levels. And yes, it is in most sugar free products. Things I have found that are ok : plain Diet coke, jay robb protein powder, Da vinci syrups…

Vitamin water zero and Sobee zero do not have Ace K in them. I bought some flavored rice snack cakes, read the ingredients to late. Now I check the ingredients on everything. Just happy to hear that a doctor mentioned the link between Ace K and diabetes!

I personally did better without diet sodas or energy drinks on The Carb Nite Solution. Fat loss was prevalent with Ace-K in my diet, but I feel as though I was losing much more water weight than body fat.

I would agree that the Carb Nite Solution works better if you cut out Ace-K. I was drinking Sparkling Rockstars before every workout the last few cycles of CNS (not to mention that I was working out 5-6 days a week), but eventually, the fat loss took a turn. I didn’t realize that Ace-K had an effect on insulin until recently, and now I look back and see why the diet didn’t work as efficiently. When I did CNS the time before that (several months ago), I wasn’t consuming any Ace-K as far as I remember, and body fat dropped much more quickly. I got down to around 10% BF with no issues (in once cycle, starting from 11-12%). Of course I screwed up a few times and overate just to gain back the pounds (CBL way too many carbs without exercise..hehe..), but I’ve learned a lot from my mistakes. The next time I do another few cycles of CNS, I will be sure to rid of Ace-K from the diet.

I’ve been consuming my energy drinks after my workout recently, and I’m going to run this experiment for a while to see if still causes issues, but my guess would be that it would be safe to do so according what I’ve read from CBL and CNS.

Hi Brandon – there are too many variables at play to be able to say on an individual basis whether Ace-K was the determinant factor, even if you were tracking the key variables, hence using the studies as a guideline. However, if you feel that fat loss is better without ace-k, then no harm in removing it, particularly if you feel more comfortable that way. Our advice would be to track the variables tightly, see what the calories were and then draw your conclusions :)

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