If you've ever seen the hashtag #MeatlessMonday, you've probably jumped to the right conclusion about what the term means. People give up meat for one day a week to improve their healthy and the health of the planet. There are countless Pinterest boards devoted to the subject and even a number of books. The routine actually developed during World War I, when Woodrow Wilson called for Americans to reduce consumption to help the war effort, but it was revived as a public health awareness program in the States in 2003, and since has become a global phenomenon. In 2009, Paul McCartney and his daughters even launched their own Meat Free Mondays campaign. Needless to say, it has taken off, but why?