The twist is the answer, which is that all of them are vegans. Each picture appears with a profile about the person and ends with the question: "Want to look this healthy? Visit www.vegansociety.com."
Gerry McCusker, a director at Limone Media, said: "The idea behind this project is to produce a quick and clean form of communication that would ultimately achieve increased click-through numbers on to the Vegan Society's main website to grow its member base."
The Vegan Society promotes vegan lifestyles, which seek to exclude as far as possible the use of animals in food, clothing or any other purpose.
A spokesperson for the society said: "Our hope is that upon receiving this viral communication, existing members will feel inspired to forward the email to share the pleasures of veganism among friends and family."
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