Jay Z and Beyoncé. Picture: Beyonce.com

Beyonce and Jay Z are challenging fans to go vegan in exchange for free concert tickets for life.

The couple have unveiled the Greenprint Project after penning the forward for Marco Borges' new cookbook 'The Greenprint: Plant-Based Diet, Best Body, Better World'. They are giving one lucky fan who pledges to go vegan a chance to get their hands on tickets to their concerts for the next 30 years.

Marco - who is the founder & CEO of 22 Days Nutrition, a plant-based lifestyle solutions company - told vegan news website LiveKindly: "Greenprint is the positive impact we can have on the world (and our health) by eating plant-based meals. It's about getting people to understand the power we have to effect change through our food choices. It is our responsibility to leave this planet better than we found it for all future generations."

Marco inspired Jay Z and Beyonce to start a plant-based lifestyle and said the power couple were unable to "ignore" the positive hype surrounding a plant-based diet, adding: "They got to a point where they realised that the overwhelming information about the benefits of a plant-based diet were too hard to ignore. So they decided they wanted to challenge themselves and others to move towards a plant-based diet."

Beyoncé announced last Spring that she was adopting a vegan lifestyle as she prepared to headline Coachella festival, which took place in April 2018.

Writing on Instagram at the time, she shared: "44 days until Coachella!! Vegan Time!!"

And in 2015, Beyonce praised her personal trainer's vegan plan and said it made her skin "firmer" and a "lot tighter."