Perhaps Hitler became a "vegetarian" during WWII (for health reasons, fear of contamination or scarcity of meat) but it is well documented that he continued, even during this period, to eat his favorite dish, Liver dumplings. His love of squab and Bavarian sausage is also well known.
And it was before WW2. He thought it to be cool and showed extreme strength and willpower. Nazi leaders, including Hitler and Hermann Göring etc, were supporters of animal rights and conservation, many were vegetarians and they (surprisingly) put in place the most advanced animal protection laws that are still the same in Germany. And many say, are still the most advanced in the world.
Here for you to read some more