That was a myth put out by Goebbels to show that the Fuhrer was dedicated to the German people and practised self-denial. It's true that his diet was mainly vegetable based but there are various sources, including his personal chef, who attest to the fact that he ate meat. He also occasionally...
When I was at uni, the chairman of the student Tories was a vegetarian and hunt saboteur. Alan Clark, the right wing diarist and minister, was also a strident veggie.