5 Good Reasons Diet Coke Isn’t Keto

This article is based on scientific evidence

Diet Coke | Gut Health | Weight Gain | Keto-Friendly Drinks | Ketosis

There are a lot of unanswered questions about diet soda on keto. Diet Coke looks like a good alternative for keto. It contains zero grams of net carbohydrates, protein, and zero calories.

But why do so many overweight people drink diet soda? And why do they seem to consume these sugar-free drinks in incredible quantities?

In this guide, I look closely at natural and artificial sweeteners.

By doing so, I provide you with the five most critical science-based arguments for why diet and zero drinks are a bad option for keto.

Moreover, I suggest alternatives you can safely drink on the keto diet.

Is Diet Coke Keto?

There is a lot of confusion about diet coke and the keto diet:

  • Does diet soda kick you out of ketosis?
  • Is coke zero generally unhealthy?
  • What is the difference between diet coke and coke zero?
  • Does diet soda help you lose weight?

Having been plagued by the topic for a long time, I’ve worked through numerous studies and put sweeteners on keto under the microscope.

Risks of Diet Coke on Keto

Marketing tells us nothing about the downsides of low-calorie drinks. However, we are discussing synthetically colored carbonated water with artificial sweeteners and chemical additives.

Sugar-free drinks with no calories or carbs should be ideal for the ketogenic diet. Is it all that simple?

Here are five significant side effects of diet soda that prevent weight loss.

Infographic - 5 Reasons Why Diet Soda on Keto Is Bad for You

1. Harms Gut Health

Synthetic sweeteners in diet soda like aspartame, saccharin, sucralose, and others are known to alter your gut microbiome.

They are killing so-called “good” microbes while supporting the overrun of your gut microflora with harmful bacteria (Gundry et al. 2017).

Saccharin, sucralose, and the natural sweetener stevia are known to change the composition of the gut microbiome (Ruiz-Ojeda et al. 2019).

According to research, a single package of the sucralose-based sweetener Splenda eradicates 50 percent of healthy gut microflora (Abou-Donia et al. 2008).

With this in mind, such a rise of “bad” gut microbes is causing an immunological reaction in the body resulting in fat storage and weight gain with diet soda intake.

Furthermore, an additional artificial sweetener on everyone’s lips recently called acesulfame potassium. So, what is acesulfame potassium?

It’s the second artificial sweetener besides aspartame in coke zero, while diet coke only uses aspartame. Hence, acesulfame potassium is not the same as aspartame on keto.

Nevertheless, it’s as sweet as aspartame and 200 times sweeter than table sugar.

But compared to sucralose, acesulfame K is just one-third as sweet. Given that it’s more resistant to heat and acids than aspartame, does that make acesulfame potassium keto?

Certainly not. Instead, acesulfame potassium’s side effects are dangerous and aren’t safer than other artificial sweeteners on keto.

Likewise, recent research revealed that acesulfame potassium also alters the gut microbiome. Additionally, it supports body weight gain (Bian et al. 2017).

And the nail in the coffin is that acesulfame potassium on keto might affect your cognitive brain function (Ibi et al. 2018).

In short, acesulfame potassium is as bad for you as aspartame on keto.

While many think diet soda supports weight loss, the opposite is true.


Artificial and natural sweeteners are changing your gut microbiome health for the worse. Consequently, diet soda is bad for you in general. 

A woman is caring about her gut health while experiencing side effects of the artificial sweeteners aspartame and acesulfame potassium after consuming diet coke.

2. Encourages Fat Storage

From a historical perspective, sweet taste used to be rare. Nature provided sweet taste in the form of ripe summer fruits and honey. Moreover, in medieval times, honey was the only sweetener.

Fruits and honey rich in fructose – a significant driver of insulin resistance in liver cells and obesity – could have been our Stone Age ancestors’ ticket for survival.

If they found something sweet, nature made sure that humans ate it.

Not to mention that today’s fruits are candy on a tree compared to their ancestral versions. For example, the apples of the middle ages (crab apples) were almost inedible, and wild strawberries used to be way smaller.

The first sugar cane plantations evolved in the days of the crusaders. Since it was a luxury good until the 19th century, sugar was mainly used for medicine and rarely to cook.

Consequently, people didn’t eat sweet dishes at all.

The sweet taste was seasonal for hundreds of thousands of years and of limited availability due to natural events.

Therefore, our bodies still realize it as an evolutionary signal for storing fat to survive wintertime. But our bodies are experiencing an endless summer thanks to artificial sweeteners and sugar.

Since it disturbs its circadian clock, the 24/7 availability of sweet taste is comparable to jet lag in the human body.

Besides the 24 hours based circadian clock, one is tied to the moon cycle representing a sense of seasons (Gundry et al. 2017).

Fruit season used to be vital for survival. But since evolutionary yesterday, we have been disrupting the circadian rhythm.

Because we are consuming dietary fructose and sweetened drinks like diet coke all year round, we are gaining weight.


The sweet taste is an evolutionary signal to the body, stimulating fat storage to survive winter. Since it’s not about sugar, non-caloric sweeteners effectively promote body fat.

Strawberries and sweet taste used to be limited to summer fruit season harvest, but diet soda  on keto brings sweet taste and weight gain whole year-round

3. Promotes Cravings

Have you ever asked yourself why we are so sensitive to sweetness and why it seems the most addictive taste? An excellent reason is that two-thirds of our taste buds are responsible for sweet taste.

The big caveat to the evolutionary sensitivity to sweetness is that sugar molecules and those of artificial sweeteners bind to the tongue’s receptors. In other words, diet soda makes our brains greedy for sweet tastes.

Because compared to salty taste, sweetness has a positive feedback system. It’s more likely to get you addicted. The more you consume, the more you crave.

If the brain awaits sweetness and glucose but gets non-caloric sweeteners, it overcompensates with more appetite and cravings for sweet food (Yang 2010).

Moreover, functional magnetic resonance imaging studies showed that sucralose does not fully activate the brain’s reward center, like glucose (Smeets et al. 2005).

Consequently, the brain strives towards fully activating the reward center, making it more likely to develop cravings and a bad habit of eating sweets.

With that in mind, researchers have also found that exchanging caloric beverages with diet soda does not reduce overall calories due to increased appetite (Bellisle et al. 2007).

Recently scientists at Yale University found that the sweetness intensity indicates the energy preserved in food to our brains.

Therefore, diet soda can confuse the nutritional value signal and the metabolic response.

Since a sweetened, non-caloric drink can trigger a more significant metabolic response than a sugary beverage, diet soda on keto is bad (Veldhuizen et al. 2017).


Artificial sweeteners confuse our brains by only partially stimulating the reward center and fostering cravings for sweets. Furthermore, the metabolic response is irritated due to the missing nutritional value of diet soda.

A monkey holds a can of diet coke and realizes that it promotes weight gain on keto

4. May Raise Insulin

Insulin, not calories or lack of physical activity, is the ultimate driver of obesity. With this in mind, it does not matter if food raises blood sugar levels as long as it elevates insulin (Fung 2016).

Therefore, we need to look at the insulin response to artificial sweeteners. Sucralose doesn’t bring glucose or calories into your body but elevates insulin levels by 20 percent.

Likewise, other artificial and natural sweeteners like stevia stimulate insulin (Pepino al. 2013). 

Nevertheless, common sweeteners such as aspartame and stevia almost don’t impact blood sugar levels. But they raise insulin more significantly than table sugar (Anton et al. 2010).

Although diet drinks on keto may not bring additional carbs, sugar, or even calories, they encourage your body to produce insulin. And the hormone induces weight gain.

Since diet soda raises insulin levels, diet soda can affect ketosis and promote weight gain thanks to the storage hormone.

A single diet coke might not kick you out of ketosis, but a significant amount can do.

Furthermore, diet coke on keto increases the risks of metabolic syndrome, strokes, and heart attacks.


Non-caloric sweeteners can elevate insulin levels more than regular sodas. Consequently, you promote modern diseases and weight gain by drinking diet soda on keto.

A silver can of diet coke on keto is a bad idea since it raises insulin levels

5. Makes You Sick

Here’s a general question induced by statistical evidence. If diet soda is at least neutral regarding weight gain, why did its consumption and obesity skyrocket in the last decades?

The University of Texas Health Sciences Center at San Antonio found that instead of supporting weight loss, the probability of weight gain with diet soda increased by a mind-blowing 47 percent. 

Dr. Sharon Fowler, who led the study, concluded that artificial sweeteners’ side effect is the fueling rather than mitigating the obesity epidemic (Fowler et al. 2008).

Moreover, the American Cancer Society aimed to demonstrate that diet soda fosters weight loss by surveying 78,694 women during an epidemiology study.

But the outcome wasn’t what they expected. Women consuming artificial sweeteners were significantly more likely to gain weight (Stellman and Garfinkel 1986).

And the list goes on. The Framingham Heart Study found that diet soda consumers are 50 percent more likely to develop metabolic syndrome (Dhingra et al. 2007). 

Furthermore, the Atherosclerosis Risk in Communities Study (ARIC) showed a 34 percent higher incidence of metabolic syndrome for diet soda users (Lutsey and Steffen et al. 2008).

But artificial sweeteners don’t just increase the risk of obesity.

The Women’s Health Initiative Observational Study observed 59,614 women over 8.7 years. The outcome? Participants drinking two or more diet sodas daily faced a 30 percent higher risk of cardiovascular events (ACC 2014).

And that’s consistent with a study conducted at the University of Miami, yielding a 43 percent increase in strokes and heart attacks for diet soda users (Gardener et al. 2012).

Do you see why diet soda on keto is a bad idea? Because there are heaps of evidence that it significantly supports weight gain and the risk of cardiovascular diseases.


Diet soda isn’t supporting weight loss at all. Instead, it fosters weight gain, diabetes, strokes, and heart attacks.

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Will Diet Coke Kick Me Out of Ketosis?

Since we know that aspartame in diet coke raises insulin levels, it’s not generally safe for keto (Anton et al. 2010).

Nevertheless, one diet coke will not necessarily kick you out of ketosis if you’re fat-adapted.

What does this mean in practice?

If there is an occasion where you have to choose between a single diet coke or regular coke, pick the diet coke. Similarly, a single coke zero is less likely to kick you out of ketosis.

But if you overconsume artificial sweeteners, you’ll also be kicked out of ketosis. So let diet coke on keto be the exception – a single can if there is no keto-friendly beverage option.

Moreover, the negative impacts of diet coke on overall health and cravings might even outweigh the consumption of regular coke in the long run.

Keto-Friendly Diet Coke Alternatives

Since we have concluded that we shouldn’t have diet soda on keto, it’s time to come up with keto-friendly beverages as alternatives.

Moreover, the impact of alcohol and diet coke on ketosis is not apparent and often misjudged. Therefore, I have to tackle these topics for you in more detail.

Diet Soda Substitutes

It’s not always easy to bring variety and flavor into drinks on a keto diet. Therefore, keto-friendly beverages are excellent for hydration and can even help suppress hunger.

So here’s a list of what you can drink on the keto diet and an intermittent fasting schedule without regrets:

  • Water with a squeeze of lemon or lime
  • Water with slices of oranges or cucumber
  • Carbonated Water
  • Mineral Water
  • Black Coffee
  • Black Decaf Coffee
  • Green Tea
  • Black Tea
  • Oolong Tea
  • White Tea
  • Herbal Tea (check ingredients for sweeteners and fruits)
  • Diluted Apple Cider Vinegar

And remember, all these beverages are keto-friendly as long as they are not sweetened and without milk. If you want to substitute milk and are not fasting, you can go for the following:

  • Heavy Whipping Cream
  • Gras-fed Butter
  • Ghee
  • Coconut Milk
  • Coconut Oil
  • MCT Oil

Moreover, you can also safely add cinnamon or nutmeg for flavor.

Even alcohol is a better idea than diet soda on keto

Beverages to Avoid

Additionally, here’s a list of beverages that you might think are keto-friendly but aren’t:

  • Diet Soda
  • Diet Coke
  • Coke Zero
  • Zero Drinks
  • Energy Drinks
  • Zero Energy Drinks
  • Sugar-Free Energy Drinks
  • Vitamin Water
  • Vitamin Water Zero
  • Protein Shakes
  • Iced Coffee Drinks
  • Smoothies
  • Freshly-squeezed juices

Since separating the protective fiber in fruits from fructose and glucose can result in an insulin spike, “natural” juices are out. Moreover, a load of fructose contributes to insulin resistance and fatty liver.

Keto-Friendly Drinks With Alcohol

Alcohol on keto 🥃 can inhibit your liver from focusing on other metabolic tasks.

But if you want alcohol on rare occasions, keep your hands off cocktails 🍹.

I always prefer pure liquor with sparkling water over cocktails. In short, don’t add fructose and glucose to the alcohol.

Wine 🍷 is more convenient since it contains less residual sugar than you might think if it’s a dry white wine:

  • Chardonnay
  • Sauvignon Blanc
  • Pinot Grigio

Nevertheless, I prefer dry red wine because of its many antioxidants. But how much red wine is healthy?

According to research, 3 ounces or 0.7 glasses of red wine yield the lowest heart disease risk for women, while 6 ounces or 1.4 glasses a day for men (Corrao et al. 2000).

And the best time to drink red wine is with meals because it prevents blood pressure, glucose, and insulin levels from rising (Shai et al. 2007).

So, which red wine is dry and has the least sugar?

  • Pinot Noir (2.3 grams carbohydrates, 0 grams sugar)
  • Gamay (2.4g, 0g)
  • Cabernet Franc, Merlot (2.5g, 0g)
  • Cabernet Sauvignon, Syrah (2.6g, 0g)

Additionally, a wine app simplifies your life.

In contrast, beer 🍺 is a worse choice since more carbohydrates accompany alcohol. If you still want to have a beer, pick quality over quantity.

For example, craft beer has higher quality ingredients and comes in smaller portions.

Although alcohol is traditional on many celebrations, keep the amount and time frame of consumption small. Therefore, start drinking water before overconsuming it and feel better the next day.


The bottom line is that diet soda helps us to store fat more efficiently on keto while endangering cardiovascular and gut health.

On top of that, diet coke on keto promotes cravings for sweets. And it does not matter if a natural or artificial sweetener is used.

Yes, diet soda might have zero carbohydrates, sugar, and calories. But artificial sweeteners on keto can have the same negative impact as ordinary sugar by triggering an insulin response.

Therefore, diet soda can break a fast.

Adding human-made synthesized chemicals to your diet to reduce carbs doesn’t make sense for safety reasons, even in small amounts.

Diet soda vs. regular soda? The inconvenient truth is to go with real hydration that isn’t a meal and won’t break a fast.

Coffee and green tea are great choices since they stimulate metabolism and weight loss while reducing appetite. Carbonated mineral water is also viable and helps with noisy stomachs.

Want more flavor in your diet? A squeeze of lime or lemon and slices of oranges or cucumbers are excellent and safe choices.

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Frequently Asked Questions (FAQ)

Can you drink diet soda on keto?

No, because even non-caloric sweeteners like sucralose and stevia trigger an insulin response and promote fat storage and cravings.

What can I drink on keto diet?

Coffee ☕ and green tea 🍵 are great drink choices on keto since they stimulate metabolism and weight loss while reducing appetite. Carbonated mineral water is also viable and helps with noisy stomachs.

Does aspartame affect ketosis?

While aspartame doesn’t impact blood sugar levels, it can raise insulin more significantly than table sugar. Hence, it can kick you out of ketosis.

Will diet soda kick me out of ketosis?

A single diet soda might not kick you out of ketosis, but non-caloric artificial sweeteners in diet soda raise insulin levels. Therefore, large consumption of diet soda will kick you out of ketosis.

What is the difference between Diet Coke and Coke Zero?

The sweeteners in Coke Zero are aspartame and acesulfame potassium, while Diet Coke contains aspartame. Instead of citric acid in Diet Coke, there’s potassium citrate in Coke Zero.

Can you drink an energy drink while fasting?

You can’t drink energy drinks while fasting intermittently since even sugar-free diet drinks cause an insulin response. Hence, energy drinks can break your fast and are not keto-friendly.


A – Ga

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American College of Cardiology. Too many diet drinks may spell heart trouble for older women, study suggests. ScienceDaily. 2014 Mar 29; Retrieved 2019 Oct 9 from www.sciencedaily.com/releases/2014/03/140329175110.html

Anton SD, Martin CK, Han H, Coulon S, Cefalu WT, Geiselman P, Williamson DA. Effects of stevia, aspartame, and sucrose on food intake, satiety, and postprandial glucose and insulin levels. Appetite. 2010 Aug;55(1):37-43. doi: 10.1016/j.appet.2010.03.009. Epub 2010 Mar 18. PubMed PMID: 20303371; PubMed Central PMCID: PMC2900484.

Bellisle F, Drewnowski A. Intense sweeteners, energy intake and the control of body weight. Eur J Clin Nutr. 2007 Jun;61(6):691-700. doi: 10.1038/sj.ejcn.1602649. Epub 2007 Feb 7. Review. PubMed PMID: 17299484.

Bian X, Chi L, Gao B, Tu P, Ru H, Lu K. The artificial sweetener acesulfame potassium affects the gut microbiome and body weight gain in CD-1 mice. PLoS One. 2017;12(6):e0178426. doi: 10.1371/journal.pone.0178426. eCollection 2017. PubMed PMID: 28594855; PubMed Central PMCID: PMC5464538.

Corrao G, Rubbiati L, Bagnardi V, Zambon A, Poikolainen K. Alcohol and coronary heart disease: a meta-analysis. Addiction. 2000 Oct;95(10):1505-23. doi: 10.1046/j.1360-0443.2000.951015056.x. PubMed PMID: 11070527.

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G – R

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S – Z

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Stephan is a writer and a true man of science, holding multiple diplomas and master's degrees in different research areas. His greatest passion is closing the gap between the conventional perception of health and the latest scientific evidence – always following the data.

This Post Has 2 Comments

  1. kyle

    so I could live on diet coke alone because it turns into stored fat?

    1. Hi Kyle,

      Thanks for the question. The answer is no since diet coke is virtually empty. There will come the point where you will lack essential fatty acids, amino acids, and electrolytes.

      But you won’t last long with a diet coke-only diet since it will unleash unbearable cravings. On top of it, its ingredients will be dangerous for your overall health: CARBONATED WATER, CARAMEL COLOR, ASPARTAME, PHOSPHORIC ACID, POTASSIUM BENZOATE (TO PROTECT TASTE), NATURAL FLAVORS, CITRIC ACID, CAFFEINE.


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