This Popular Diet Soda Isn't Vegan, But The Brand Won't Reveal Why

We have been drinking flavored soda for more than a century, and big-name brands including Coca-Cola, Dr Pepper, and Sprite help slake thirsts across the United States and the world. This massive industry always looks to innovate, even if not every experiment is a success (just look at why New Coke was discontinued). That can include tailoring products to vegetarians and vegans. But while most sodas, diet or otherwise, contain no animal-derived ingredients, the same can't be said of Diet Pepsi. Adding a layer of mystery is the fact that PepsiCo, the company behind the brand, won't specify why it's not suitable for vegans.

The issue first came to light in 2017, when British newspaper Metro went in search of answers. PepsiCo confirmed, both in a social media post and in a statement sent to the paper, that Diet Pepsi was only suitable for vegetarians, as it contained "traces of ingredients that are not suitable for people following a vegan diet." The company went on to add that vegans and vegetarians could drink regular Pepsi and Pepsi MAX. The plot thickened when Britvic, the United Kingdom's Pepsi producer and distributor, told Metro they didn't know exactly what ingredient prevented Diet Pepsi from being vegan, as it was apparently part of a proprietary formula.

Although recipes like those for Coca-Cola are still a closely-guarded secret, manufacturers are obliged to inform consumers about the ingredients in products (albeit with a few exemptions), including animal-based items. That includes traces of fish, pork or beef gelatin, cochineal (a red coloring derived from crushed insects), and even honey and vanilla. Cream soda can contain traces of dairy, sports and energy drinks can include vitamin D extracted from sheep's wool, and ester gum, made from the sweetener glycerol, can be derived from animals. The food dye Yellow #5 is tested on animals, though Pepsi is rumored to be trialing a version of Mountain Dew without the signature colorant. 

While the current labelling system for vegan-friendly foods and drinks isn't perfect, vegans and vegetarians can a more-informed choice than in years gone by. The mystery of what makes Diet Pepsi non-vegan has led some to speculate the ingredient itself may be tested on animals, making it a dealbreaker for many consumers, not just vegans.

Frustratingly, we found that sourcing vegan soda was easier said than done. Some online lists were a few years old or even contradicted themselves. Coca-Cola's Hong Kong website lists sodas that vegans can happily drink, but the U.S. site doesn't, so it's down to consumers to know the source of all the ingredients. Meanwhile, the Pepsi site returned no results when we used its product finder to find vegan-friendly soft drinks. Given some of the other unsettling facts about diet soda, maybe it's a good time to switch to water?