Those who follow a plant-based diet may want to consider avoiding adding a slice of lemon to their drinks because they are not always vegan.

Cookbook author Jack Monroe recently questioned on Twitter why a Pizza Express menu said a glass of Coca Cola would only be vegan if “served without lemon”.

Attaching a picture of the menu, Monroe wrote: “Erm, what do Pizza Express do to their LEMONS to make them not suitable for vegans?! Just noticed this and can’t for the life of me fathom wtf.”

But, according to Pizza Express and others who responded, it is the wax applied to the citrus that makes it unsuitable for vegans.

In response to Monroe’s confusion, Pizza Express wrote: “The wax on waxed lemons contain shellac, which is derived from insects and therefore strictly not vegan.”

Lemons and other fruits are waxed to maintain their appearance and freshness. In addition to shellac, made from a resin secreted by the female lac bug, waxes may be made from beeswax, which is also not strictly vegan.

Fortunately, there are some fruit waxes, such as polyethylene wax, that are suitable for a plant-based diet.

Celebrity Vegans: From Beyoncé to Natalie Portman Show all 13 1 /13 Celebrity Vegans: From Beyoncé to Natalie Portman Celebrity Vegans: From Beyoncé to Natalie Portman Miley Cyrus The pop singer is a passionate animal rights advocate, telling Vanity Fair in 2019 that her diet also reflects her fashion choices: "I’m challenging the system more than ever. Choosing to live as a sustainable vegan activist means wearing more vintage (less waste; loving pieces for longer), playing with the newest eco-materials and technology, and making custom vegan pieces with some of my favorite designers." Getty Celebrity Vegans: From Beyoncé to Natalie Portman Alicia Silverstone The Clueless star went vegan shortly after wrapping the hit 1990s film and has been a passionate campaigner for animal rights since. Speaking in a video for Compassionate Meals in 2017, she said: "Knowing the truth about where our food comes from is just so disturbing to me. Once you see it, there’s no way to go back from that for me." Getty Celebrity Vegans: From Beyoncé to Natalie Portman Simon Cowell The music mogul revealed in a recent interview with The Sun that he decided to give up animal products earlier this year "on a whim", adding that he feels much better as a result. Getty Celebrity Vegans: From Beyoncé to Natalie Portman Venus Williams "I started for health reasons," Williams told Health in 2019. "I was diagnosed with an autoimmune disease, and I wanted to maintain my performance on the court. Once I started I fell in love with the concept of fueling your body in the best way possible. Not only does it help me on the court, but I feel like I’m doing the right thing for me." Getty Celebrity Vegans: From Beyoncé to Natalie Portman Natalie Portman The American-Israeli actor decided to go vegan eight years ago after learning more about the environmental consequences of eating animal products. Speaking at an Environmental Media Awards benefit, 2017, she said: "Factory farming is responsible for most of the air, water, and land pollution - that disproportionately affects our poor communities as well. So we get to make decisions three times a day, what we do with our planet, and you can make a difference by even once a day or once a week choosing not to eat animals or animal products." AFP/Getty Celebrity Vegans: From Beyoncé to Natalie Portman Beyoncé While she chooses to refer to herself as plant-based as opposed to vegan, the 'Halo' singer underwent a 22-day vegan challenge with husband Jay-Z in 2013 and is believed to have maintained the diet ever since. Writing in the foreword of The Greenprint: Plant-Based Diet, Best Body, Better World by Marco Borges, the couple say: "We used to think of health as a diet – some worked for us, some didn’t. Once we looked at health as the truth, instead of a diet, it became a mission for us to share that truth and lifestyle with as many people as possible." Getty/Coachella Celebrity Vegans: From Beyoncé to Natalie Portman David Haye The British boxer extolled the virtues of veganism in an interview with The Daily Telegraph in 2016: "A lot of the meat that people eat has been genetically modified, or if it hasn’t then the food the animal’s been fed has been. That’s tough for a human being to process, so cutting it out made me feel immediately better and stronger than ever." Getty Celebrity Vegans: From Beyoncé to Natalie Portman Ariana Grande The 'Dangerous Woman' singer announced she was going vegan in November 2018. Speaking to The Daily Mirror in a recent interview, she explained: "A lot of the meat that people eat has been genetically modified, or if it hasn’t then the food the animal’s been fed has been. That’s tough for a human being to process, so cutting it out made me feel immediately better and stronger than ever." AFP/Getty Celebrity Vegans: From Beyoncé to Natalie Portman Ellie Goulding The British singer has been toying with veganism for a while, having been a vegetarian for seven years. Speaking to The Cut in 2018, she revealed that she will "never eat fish or meat again" and eats a predominantly vegan diet. Getty Celebrity Vegans: From Beyoncé to Natalie Portman Mike Tyson The former heavyweight boxing champion revealed he had become vegan in 2010. "I wish I was born this way," he told Fox News in 2011. "When you find out about the processed stuff you have been eating. I wonder why I was crazy all those years." Getty Celebrity Vegans: From Beyoncé to Natalie Portman Jessica Chastain The Zero Dark Thirty star decided to go vegan roughly 13 years ago because of low energy. Speaking to W Magazine in 2017, she clarified: "being vegan was not anything I ever wanted to be. I just really was listening to what my body was telling me." Getty Images Celebrity Vegans: From Beyoncé to Natalie Portman Rooney Mara Mara has been vegan for eight years, telling Harper's Bazaar in 2018 "it’s better for your health and the environment.” Getty Celebrity Vegans: From Beyoncé to Natalie Portman Kim Kardashian Reality star Kim Kardashian West revealed that she has started eating a plant-based diet on Instagram in April 2019. Sharing two photographs of vegan dishes on her Instagram story, the 38-year-old wrote: “I am eating all plant-based when I am at home.” Getty

However, if you follow a strict vegan diet, it is worth asking the grocery store or restaurants which type of wax is used on the produce, or only purchasing non-waxed fruits and vegetables.

While some people were shocked by the news, others praised the restaurant chain for its dedication to customers’ food preferences.

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