Diet Coke vs. Coke Zero Sugar: Which Sugar-Free Soft Drinks Is the Healthier Option?

We all have our vices, right? Being from the Midwest, I grew up on pop (or soda, as the rest of the country calls it). For a long time, I was a regular, classic Coca-Cola girl. I just couldn't get into the taste of Diet Coke even though I knew I was consuming a lot of sugar. Then, Coke Zero came along, and I found a new favourite. I felt like I could indulge my craving for a sweet, carbonated beverage with less risk to my health.

Today, the Coke Zero I fell in love with doesn't technically exist. Both Diet Coke and Coke Zero Sugar (what was formerly Coke Zero) have new formulations and, in the first case, even a few new flavors. Looking at the two "new" sugar-free options got us wondering if there was any real difference, from a health and nutritional standpoint, between the two. We asked Lori Chong, a registered dietitian and certified diabetes educator working at Ohio State University's Wexner Medical Center in Columbus, OH, to break it down for us.

What are the different ingredients in the two sodas?

Diet Coke and Coke Zero Sugar share very similar ingredients, according to nutrition facts listed on Coca-Cola's website. Both options contain sodium, phenylalanine (an amino acid), carbonated water, caramel colour, phosphoric acid (an acid that gives soda a tangy flavour and prevents mould and bacteria), aspartame (a nonsaccharide sweetener), potassium benzoate (a food preservative), natural flavors, and caffeine. The two sodas also include ingredients sourced from genetically engineered (GE) crops, which are commonly referred to as genetically modified organisms (GMOs).

So are they basically the same?

Although the ingredients in Coke Zero Sugar are relatively similar to those in Diet Coke, there are a few slight variations, according to Chong. "It appears from the order of the ingredients that Coke Zero Sugar has more phosphoric acid than Diet Coke," she said. The ingredient with the highest concentration in a recipe is usually listed first, and the rest go from there in decreasing order.

Coke Zero Sugar has slightly less sodium (25 mg in a 12-ounce serving compared to 40 mg per can of Diet Coke). The former also has slightly less caffeine at 34 mg in each can, compared to 46 mg in a can of Diet Coke.

The main difference in the ingredient lists is Diet Coke contains citric acid, while Coke Zero Sugar does not, instead naming potassium citrate and an additional artificial sweetener called acesulfame potassium. Citric acid and potassium citrate are both acidity stabilisers, so, again, the recipe differences are minor.

Of course, not every ingredient in the popular sodas is explicitly listed on the back of each drink. Coca-Cola's secret is behind its mix of natural flavors, which are proprietary to the brand and, therefore, not released.

Which one contains the healthiest artificial sweetener?

There don't seem to be major differences between aspartame (in both Diet Coke and Coke Zero Sugar) and acesulfame potassium (only in Coke Zero Sugar) when it comes to nutrition and potential health risks, but that doesn't necessarily mean either is particularly good for you.

"Both are generally recognised as safe, per FDA standards, however, safety concerns remain," Chong said. Some health and wellness experts, like those at the Center for Science in the Public Interest, recommend you avoid both aspartame and acesulfame potassium altogether, but studies conducted have been too small and inconclusive.

You might have noticed a warning regarding phenylalanine right below the ingredient list on both sodas. The Mayo Clinic says the amino acid is not a health concern for most people, but it can be a serious health concern for those who have the genetic disorder phenylketonuria (or PKU, the natural buildup of phenylalanine in the body). Phenylalanine is found in aspartame, so that's why you can spot that warning on both Diet Coke and Coke Zero Sugar.

Alright, which soda is the healthiest?

Aside from the artificial sweetener, there are no significant nutritional differences between Diet Coke and Coke Zero Sugar, Chong said. "I believe they are just trying to appeal to different taste preferences," she said. "Diet Coke has been around a long time and has been very popular, but not everyone likes it."

Chong also speculates that the newer of the two, Coke Zero Sugar, may have been created to appeal to a wider audience. "They may have wanted to have a sugar-free soda that didn't have the word 'diet' in the name," she said. Either way, it turns out you can enjoy your preferred sugarless Coca-Cola drink without worrying that your taste buds have chosen the less healthy option for you.

Be mindful, though, as you satisfy your cravings that there are a lot of verified, and some uncertain but highly likely, health risks associated with drinking a ton of sugar-free soda.