Is Diet Coke Keto and Actually Good for Weight Loss?

This article is based on scientific evidence

Many people starting a ketogenic diet seek ways to satisfy their cravings for sweets. At first sight, Diet Coke looks like an excellent option for the keto diet. It contains no carbs and protein and has zero calories, but you must look deeper for a reliable answer.

In this article, I go well beyond the conventional nutritional value analysis to determine if Diet Coke is keto and can satisfy cravings for sweets.

Although light drinks are calorie-free, it’s essential to understand that they will affect your body if you’re on a keto diet.

Here, we will explore ingredients, artificial and natural sweeteners, and their impact on ketosis. We will also consider scientific research to provide an informed answer to this burning question.

For me, other intriguing questions arise. Why do so many overweight people drink rough amounts of light drinks? And why are they overweight anyway?

You’ll find all the answers in this article. In addition, I suggest good alternatives that you can drink without hesitation on the keto diet.

Table of Contents:

Is Diet Coke Keto?

Technically, Diet Coke is keto-friendly. However, diet soda contains additives that can interfere with metabolism and inhibit weight loss.

We need to look at nutrition facts and ingredients to draw informed conclusions.

How Many Carbs Are in Diet Coke?

According to the U.S. Department of Agriculture Research Service, 100 ml of Diet Coke has the following nutritional values (USDA 20231):

  • Energy: 0 calories
  • Protein: 0 grams
  • Fat: 0 grams
  • Carbohydrates: 0 grams
  • Dietary fiber: 0 grams
  • Sodium: 0.01 grams
  • Caffeine: 0.009 grams

But diet soda isn’t just water with salt and caffeine.

What Are the Ingredients of Diet Coke?

The ingredient list of Diet Coke from Coca-Cola includes (USDA 20232):

  • Carbonated water
  • Caramel color
  • Phosphoric acid
  • Aspartame
  • Potassium benzoate
  • Natural flavors
  • Potassium citrate
  • Caffeine

We find colors, flavors, preservatives, and other chemical additives that can contribute to metabolic and intestinal disorders (Hrncirova et al. 20193Partridge et al. 20194).

That artificial additives can be harmful is nothing fundamentally new. What many people do not reckon with is that sweeteners can have equally harmful effects.

In the case of Diet Coke and many other diet sodas, the sweetener is aspartame.

What is the difference between Diet Coke and Coke Zero?

Diet Coke contains only the artificial sweetener aspartame, while Coke Zero contains aspartame and heat-resistant sweetener acesulfame potassium (USDA 20235).

Diet Pepsi Cola vs. Diet Coke (Coca-Cola)

Diet Pepsi Cola uses acesulfame potassium and sucralose instead of aspartame as sweeteners and has 0.04 g of carbs per 100 ml, while Coca-Cola’s Diet Coke has none (USDA 20236).

Side Effects of Diet Coke on Keto

Marketing tells us nothing about the downsides of non-nutritive sweeteners in diet soda.

Sugar-free drinks with no calories or carbs sound ideal for the ketogenic diet. But artificial and even so-called “natural” sweeteners share five significant side effects that prevent weight loss:

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

1. Harms Gut Health

Sweeteners in light beverages such as aspartame, saccharin, sucralose, and stevia alter the gut microbiome (Ruiz-Ojeda et al. 20197).

They kill off the “good” microbes while supporting the flooding of the gut flora with harmful bacteria.

According to research, a single packet of the sucralose-based sweetener Splenda is enough to wipe out 50 percent of healthy gut flora (Abou-Donia et al. 20088).

In the case of acesulfame potassium, a recent study even suggests that it can upset healthy gut flora and cause obesity and inflammation (Bian et al. 20179).

An increase in “bad” gut bacteria can initiate an immunological response in the body that leads to fat gain and weight gain.

Although many think that light drinks help with weight loss, this research suggests otherwise.

2. Encourages Fat Storage

Historically, sweet taste was somewhat of a rarity. Nature revealed sweetness only in the form of ripe summer fruits and honey. That’s why honey was the only common sweetener in the Middle Ages.

Fruits and honey are rich in fructose (the sweet molecule besides glucose in table sugar), which increases fat production in the liver and is a risk factor for insulin resistance in liver cells (Aeberli et la. 201310).

Nevertheless, they could make the difference between life and death for our Stone Age ancestors. Provided they found something sweet, nature ensured that people ate it to put on body fat for the winter.

For hundreds of thousands of years, the sweet taste was limited to one season and often limited in availability due to natural events. That’s why our bodies still recognize it today as an evolutionary signal to build fat to survive the winter.

Today, thanks to sugar and sweeteners, we experience an endless summer.

Accordingly, the constant availability of the sweet taste is comparable to jet lag for the human body, as it disrupts the biorhythm.

Once upon a time, the autumn fruit season was essential for survival.

But since evolutionary yesterday, we have been disrupting biorhythms with masses of fructose and by gulping down diet soda throughout the calendar year.

But how can a zero-calorie beverage without sugar lead to weight gain?

3. May Raise Insulin

Insulin, not calories or lack of physical activity, drives obesity and metabolic syndrome.

The fat-storage hormone insulin has an antilipolytic effect (Jensen et al. 198911).

That is, it prevents fat breakdown by enzymes (lipolysis) and, in turn, promotes fat gain (Meijssen et al. 200112).

Consequently, it does not matter if the food raises blood glucose levels as long as it raises insulin levels.

Therefore, we need to look at whether sweeteners stimulate insulin production.

Indeed, aspartame and acesulfame potassium do not directly increase blood glucose (Kim et al. 202013).

However, ace-K does promote insulin secretion in the pancreas (Liang et al. 198714).

In rats, acesulfame-K increased insulin levels, but not blood glucose, in a dose-dependent manner, as did the same amount of glucose (Liang 198715).

For aspartame and sucralose, studies yield contradictory results in this context (Ahmad et al. 202016).

The results are particularly evident for “natural” sweeteners. Stevia and monk fruit directly stimulate insulin release in pancreatic beta cells (Jeppesen et al. 200017Zhou et al. 200918).

While Coke Zero does not add additional carbohydrates, sugars, or calories to a ketogenic diet, it can stimulate insulin production. Because of stevia, the same is even more true for Green Cola.

Sweeteners stimulate insulin production: some less, some more.

For example, researchers found no significant difference in blood glucose and insulin response between a lunch beverage sweetened with sugar and one sweetened with aspartame, stevia, or monk fruit (Tey et al. 201719).

Accordingly, the that sweeteners are absolute miracle cures for weight loss is a myth.

Fortunately, some studies investigate the link between diet soda and weight loss. And we will now take a closer look at them.

A silver can of diet coke for keto

4. Affects Metabolism

In 1982, Diet Coke was launched. Since then, the consumption of diet soda has been steadily increasing. However, with it, the number of obese people continues to rise.

Data from the American Center for Health Statistics show a fourfold increase in overweight teens since 1982 (Fryar et al. 202020).

Therefore, we must question whether sweeteners can serve their purpose and help with weight loss.

The University of Texas Health Sciences Center at San Antonio found that consuming diet soda increases the likelihood of weight gain by 47 percent.

Dr. Sharon Fowler, who led the study, concluded that artificial sweeteners are not a remedy but a driver of obesity (Fowler et al. 200821).

The American Cancer Society, through an epidemiology study of 78,694 female participants, wanted to prove that diet soda promotes weight loss, but the results were not as expected. Women who consumed artificial sweeteners were significantly more likely to gain weight (Stellman et al. 198622).

Accordingly, the list of studies continues. The Framingham Heart Study proved diet soda consumers were 50 percent more likely to develop metabolic syndrome (Dhingra et al. 200723). 

In addition, the Atherosclerosis Risk in Communities Study (ARIC) showed that metabolic syndrome was 34 percent more common among diet soda consumers (Lutsey et al. 200824).

But sweeteners don’t just increase the risk of obesity. The Women’s Health Initiative followed 59,614 women over 8.7 years. Participants who drank two or more diet sodas daily showed a 30 percent higher risk of cardiovascular events (ACC 201425).

This finding reinforces a University of Miami study that found a 43 percent increase in strokes and heart attacks among consumers of diet sodas (Gardeneret al. 201226).

In short, Diet Coke does not help weight loss and increases the risk of metabolic and cardiovascular disease.

5. Promotes Cravings

Have you ever wondered why we are so sensitive to sweetness and why this taste begs for more?

Two-thirds of our taste buds are responsible for sweet taste.

Although we usually think of sugar, it’s also the molecules of artificial sweeteners that bind to the receptors on the tongue.

In other words, Diet Coke makes our brains greedy for sweet taste, even on keto.

Unlike salty taste, sweetness has a positive feedback system. Consequently, it is more likely to cause one to become addicted. The more you consume, the more you crave sweets.

According to a Yale University study, when the brain waits for sweet taste, and therefore glucose, but calorie-free sweeteners are consumed, this can spur even more cravings for sweets.

These researchers also point to an interesting statistic that underscores how introducing new sweeteners significantly increased obesity between 1999 and 2004 (Yang 201027).

Magnetic resonance imaging studies show that sucralose does not fully activate the brain’s reward center, unlike glucose (Smeets 200528).

Nonetheless, the brain then strives all the more to activate the reward center fully. In short, diet soda awakens cravings for sweets.

Accordingly, researchers have found that consuming diet soda instead of caloric soft drinks does not result in the desired calorie reduction due to increased appetite (Bellisle et al. 200729).

Researchers at Yale University found that non-nutritive drinks with sweeteners elicit a stronger brain response and greater craving for sweets than sugar-sweetened beverages (Veldhuizen et al. 201730).

In short, Diet Coke affects metabolism more strongly and is more addictive than regular Coke.

A monkey holds a can of diet coke on the beach

Will Diet Coke Kick Me Out of Ketosis?

One Diet Coke won’t throw you out of ketosis if you’ve been on keto for a while. Similarly, a single Coke Zero will unlikely throw you out of ketosis.

Yet we know that aspartame affects the insulin response (Anton et al. 201031).

In large quantities, these diet sodas can throw you out of ketosis.

In practice, this means that given the choice between a Diet Coke or a regular Coke, you choose the diet soda. However, water is always the better alternative.

Is Diet Coke or Coke Zero better for Keto?

Since Diet Coke and Coke Zero can elevate insulin, both beverages are not keto-friendly. Coke Zero includes an additional artificial sweetener and might even bring more harm to your body than Diet Coke.

Continuous consumption of diet sodas hinders weight loss and increases overall health risks. Safe alternatives without sweeteners are a better choice.

Keto-Friendly Diet Soda Alternatives

Now that we know that even Coke Zero is not the ideal keto drink, here are better suggestions for a keto diet. My favorite keto drink is mineral water, which provides crucial electrolytes such as magnesium, potassium, calcium, and other minerals.

Diet Soda Substitutes

It’s not always easy to add variety to a keto diet. That’s why the following keto-friendly drinks can bring more variety into your daily routine without throwing you out of ketosis or making you hungry.

You can drink the following beverages without worry:

  • 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
  • Bone Broth

These drinks are keto-friendly as long as they are not sweetened and do not contain milk. If you miss milk and aren’t fasting, the following alternatives can help:

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 fruit juice

Keto-Friendly Alcoholic Beverages

Alcohol can keep the liver from focusing on metabolic functions. But that you must refrain from alcohol on keto entirely is not valid.

If you do drink alcohol, stay away from cocktails.

Prefer clear spirits like vodka, gin, or whiskey with sparkling water. Conventional mixed drinks, syrups, and juices are full of sugar and are usually more of a health concern than the alcohol itself.

Wine has less residual sugar than many assume, especially those low-carb wines:

  • Chardonnay
  • Sauvignon Blanc
  • Pinot Grigio

Nevertheless, I prefer dry red wine because of its antioxidants. Small amounts of wine are not unhealthy, according to research.

Women have the lowest risk of heart disease when consuming 3 ounces or 0.7 glasses of wine daily and men at 6 ounces or 1.4 glasses (Corrao et al. 200032).

The best time to drink red wine is with meals because it prevents blood pressure, glucose, and insulin levels from rising (Shai et al. 200733).

Here are the best dry red wines with little sugar:

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

In contrast, beer is a poor choice on keto because more carbohydrates come with the alcohol. For some people, even one large beer throws them out of ketosis.

My personal experience from testing ketone levels is that alcohol hardly affects ketosis as long as it is not combined with sugar or other carbohydrates or consumed excessively. However, although alcohol is a tradition when celebrating, limiting the amount and time frame of consumption is vital.

The Bottom Line

The bottom line is that light drinks don’t help us lose weight, even on a ketogenic diet. Instead, they put gut and heart health at risk.

Diet sodas fuel cravings for sweets. Any artificial or natural low-calorie sweetener stirs up cravings.

Although Diet Coke has no carbohydrates, sugar, or calories, aspartame harms metabolism and counteracts weight loss instead of promoting it.

Frequently Asked Questions (FAQ)

Can you drink diet soda on keto?

It would be better not to have diet soda on keto since sweeteners cause 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. 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, a large diet soda consumption will kick you out of ketosis.

Does Coke Zero affect Ketosis?

Acesulfame potassium and aspartame in Coke Zero elevate insulin and affect ketosis.

Can you have Coke Zero or Diet Coke on keto?

It helps not to have Diet Coke or Coke Zero on keto since their sweeteners can affect ketosis.


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Mag. Stephan Lederer, MSc.

Mag. Stephan Lederer, MSc. is an author and blogger from Austria who writes in-depth content about health and nutrition. His book series on Interval Fasting landed #1 on the bestseller list in the German Amazon marketplace in 15 categories.

Stephan is a true man of science, having earned multiple diplomas and master's degrees in various fields. He has made it his mission to bridge the gap between conventional wisdom and scientific knowledge. He precisely reviews the content and sources of this blog for currency and accuracy.

Click on the links above to visit his author and about me pages.

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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