Diet Coke vs. Coke Zero: Is One Healthier?

Coca-Cola is quite literally the most popular soda in the world, according to the latest Statista report. However, although sugary soda sales remain strong, many of us are now turning to healthy soda alternatives to satisfy our thirst and sugar cravings. That's where Diet Coke and Coke Zero Sugar come in. These two choices deliver the classic Coke flavor without the sugar or calories.

At the same time, these sugar-free favorites have sparked debates among soda lovers over which is better: Diet Coke for its distinct taste or Coke Zero Sugar for its closer resemblance to the original? The key difference between Diet Coke and Coke Zero Sugar is that both sodas use the artificial sweetener aspartame, but Coke Zero also contains acesulfame potassium (Ace-K), which can slightly alter the taste.

To help settle the debate, we put these popular diet sodas head-to-head in a taste test and consulted two registered dietitians to compare their nutrition and ingredient profiles. Here's everything you need to know about how Diet Coke and Coke Zero Sugar stack up.

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The Backstory: How These Diet Sodas Came to Be

The original Coca-Cola was the brainchild of pharmacist John Stith Pemberton, who developed the fizzy drink in 1886 in Atlanta, Georgia. By the 1960s, when the obesity epidemic started to rear its head—and subsequently, diet culture boomed and consumers started craving sugar-free alternatives—the popular drink was due for a makeover.

The concept of a "diet" Coke percolated for two decades among executives until the brand finally debuted it in the summer of 1982. Diet Coke was marketed as a "great-tasting soft drink that happens to have one calorie, rather than as a diet drink that tastes great," according to the Coca-Cola website.

Just one year after its debut, Diet Coke was the number one diet soft drink in the U.S. And from 1984 to 2010, Diet Coke trailed close behind Coca‑Cola and Pepsi as the third most popular soft drink in the U.S.

Despite Diet Coke's massive success, the brand aimed to continue innovating. The year 2005 brought about another fan-favorite: Coca‑Cola Zero, which delivered the distinct Coke flavor we know and love, minus the sugar and calories. And in 2017, the brand tweaked the recipe, packaging, and name to today's Coke Zero Sugar. "We've used our in-house innovation capabilities to make the great taste of Coke Zero even better and a lot like a Coke," the Coca-Cola press release states. "It's delicious, refreshing and our best-tasting zero-sugar Coca‑Cola yet."

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Nutritional Comparison: Diet Coke vs. Coke Zero

Diet Coke

Coke Zero Sugar

At first glance, both Diet Coke and Coke Zero Sugar appear nutritionally identical, with zeros across the board except for sodium. However, a closer examination reveals differences in phosphorus and caffeine content.

Phosphorus Content

Colas generally contain phosphorus in the form of phosphoric acid. "In addition to being a preservation agent, phosphoric acid is used to lower the product's pH (think: shelf life), [enhancing flavor and maintaining carbonation]," says dietitian Michelle Rauch, MSc, RDN.

Diet Coke contains 27 milligrams of phosphorus per serving, while Coke Zero Sugar doubles that amount with 54 milligrams.

Why is this important? "Phosphorus and calcium have an inverse relationship," Rauch says. "Too much phosphorus can decrease the amount of calcium in the body, which, over time, can lead to bone loss. Plus, it can impair absorption of other important minerals such as iron, zinc, and magnesium."

Individuals with kidney disease, those on hemodialysis, and those at risk for osteoporosis should be particularly mindful of their phosphorus intake and might want to limit or avoid these sodas.

Caffeine Content

Both Diet Coke and Coke Zero Sugar contain caffeine unless you opt for their caffeine-free versions. Diet Coke has 46 milligrams of caffeine per 12-ounce can, compared to Coke Zero Sugar's 34 milligrams. This means Diet Coke contains over 30% more caffeine than Coke Zero Sugar.

The FDA recommends limiting caffeine intake to no more than 400 milligrams per day, which equates to about 12 cans of Coke Zero Sugar or nine cans of Diet Coke.

While 34 to 46 milligrams of caffeine is less than a typical cup of coffee (which contains around 90 to 100 milligrams), it's still enough to keep you alert, so you may want to skip these sodas in the evening.

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Ingredient Comparison

The primary difference between Diet Coke and Coke Zero Sugar lies in their artificial sweetener blends. Both sodas use aspartame, but Coke Zero Sugar also contains acesulfame potassium (also known as Ace-K).

Acesulfame Potassium

Acesulfame potassium is a non-nutritive sweetener (NNS) that has zero calories and is about 120-200 times sweeter than table sugar. Due to its intense sweetness, it's used in very small amounts and often used with other sweeteners to provide a taste closely matching sugar, according to Lisa Andrews, MEd, RD, LD, owner of Sound Bites Nutrition in Cincinnati, Ohio.

According to the FDA, acesulfame potassium is safe within an acceptable daily intake (ADI) of 15 milligrams per kilogram of body weight, which equates to roughly 23 packets of sweetener or about 5 to 6 cans of diet soda daily.

Aspartame6254a4d1642c605c54bf1cab17d50f1e

Aspartame, also a non-nutritive sweetener, is made from aspartic acid and phenylalanine, two amino acids found in food and the body. Andrews notes that the phenylalanine in aspartame is changed slightly to create a sweeter taste.

According to the FDA, the ADI for aspartame is higher than acesulfame potassium and is set at 50 milligrams per kilogram of body weight, translating to about 18 to 19 cans of diet soda for a person weighing 150 pounds.

Safety and Potential Risks

Both sweeteners appear safe in moderation—that said, there have been some negative studies on both.

A 2022 review of studies in people with diabetes published in Nutrients suggests that high intake of artificial sweeteners may alter gut microbiota, potentially affecting appetite, digestion, and the risk of metabolic conditions like cardiovascular disease and obesity.

For individuals with diabetes, the consumption of aspartame and other artificial sweeteners has been associated with a higher risk of colorectal and stomach cancer, though no overall link was found between artificial sweeteners and cancer in the general population. However, these findings, from a 2023 study, involved a small number of cases, and "more research is needed to confirm this," Andrews says.

Excessive use of acesulfame potassium might also pose risks, such as potentially raising the risk of early puberty in adolescent girls, as suggested by a 2024 study. Additionally, a 2022 study on a French population cohort linked high intake of both sweeteners with an increased risk of cancer.

"Sweeteners appear to be more detrimental to those with diabetes, based on a study on the risk of liver cancer," Andrews says.

Pregnant women should avoid aspartame due to the risk of phenylketonuria (PKU), a condition where the body cannot break down the amino acid phenylalanine.

Final Thoughts on Artificial Sweeteners

Despite mixed research on the health impacts of artificial sweeteners, including some inconsistencies and reliance on diet recall data, "a recent brief from the FDA has declared NNS as safe in moderation," Andrews says.

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Taste Test: Diet Coke vs. Coke Zero vs. Original Coke

No Coke comparison would be complete without a taste test. That's why we purchased bottles of Diet Coke, Coke Zero Sugar, and original Coca-Cola to taste how they stack up against each other.

Original Coca-Cola

The OG Coke has a signature, distinct flavor that's almost metallic—the taste we associate with Coke. It boasts a bright sweetness with caramel notes that linger long after the first sip. Admittedly, it's a flavor that's hard to replicate and gives other sodas a run for their money.

Diet Coke

After taking a few swigs, we continued to crack open the bottle of Diet Coke. One gulp in, and we had no desire to go for seconds. Our first impression was it was missing that signature Coke flavor—it tasted like a bland, watered-down Coca-Cola or like a knock-off version of it.

Diet Coke's flavor ends abruptly, so you'll have to keep chugging to continue experiencing its flavor. Yet, its mineral finish and heavy artificial aftertaste that stubbornly stays on the tongue might convince you otherwise. Hard pass.

Coke Zero Sugar

At first sip, it was honestly difficult to differentiate this sugar-free version from the OG. It's fizzier than Diet Coke and boasts a much richer, complex flavor profile without the nasty mineral finish.

On subsequent sips, we found it to have a stronger (or sweeter) flavor than the original—almost like Coke Zero Sugar is trying too hard to be Coke. Some folks, especially those who don't consume artificial sweeteners often, might find that it's much sweeter than Coke and that the sweetness infringes on other flavor profiles in this zero-sugar version.

Still, we found it to be significantly more enjoyable than Diet Coke and a pretty superb alternative for those seeking soda sans sugar.

Diet Coke vs. Coke Zero Sugar: Which Tastes Better?

After tasting all three, it's clear that each has its own distinct flavor profile. Original Coca-Cola stands out with its bright sweetness and signature caramel notes that are hard to replicate. Diet Coke, on the other hand, falls short with its diluted flavor and lingering artificial aftertaste, making it the least appealing of the trio.

Coke Zero Sugar impresses by closely mimicking the taste of the original, offering a richer, more complex flavor without the mineral finish of Diet Coke. Although some might find it slightly sweeter than Coca-Cola, it remains a strong contender for those looking for a sugar-free alternative. Ultimately, Coke Zero Sugar edges out Diet Coke as our preferred choice among the sugar-free options.

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Is One Healthier Than the Other?

All factors considered, it's fair to say that neither Diet Coke nor Coke Zero Sugar is healthier than the other.

"A few diet sodas per day won't make or break your health," Andrews says. However, drinking regular Coke daily might. A single can of regular Coke contains 39 grams of added sugar, exceeding the American Heart Association's recommended daily limit.

That said, it's important to note that neither Coke Zero Sugar nor Diet Coke qualifies as a "healthy" beverage. Both contain artificial sweeteners, which could pose potential health risks for some individuals. As Andrews puts it, it's about "picking your poison" based on taste preference.

According to our taste test's verdict: Coke Zero Sugar is the clear winner. While it's markedly sweeter than Coke, it still boasts the richness and complexity you'd expect from this soda and is significantly better than Diet Coke.

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The Bottom Line

If you have a habit of drinking regular, sugar-sweetened Coke, both Rauch and Andrews advise swapping it for either Coke Zero Sugar or Diet Coke to reduce your sugar intake. "There are clearly more documented health hazards with sweetened beverages [than with diet drinks sweetened with artificial sweeteners]," Andrews says.

However, if you're not a regular soda drinker, it's best to avoid making diet sodas a habit. "Drinking an occasional Diet Coke or Coke Zero Sugar isn't going to hurt you, but if you drink one or more daily, it would be to your benefit to substitute the soda for another low- or no-calorie beverage, such as water (flavor it yourself with fruit slices), naturally flavored sparkling water, or unsweetened iced tea," Rauch says.