Of course they aren't. Hundreds of thousands of years of evolution made humans the omnivores they clearly are, with a long intestinal tract and omnivore teeth to show for it. Humans have an entire metabolic pathway for carbs. Stuff like that doesn't evolve just for fun, it evolves because it improves fitness (in the evolutionary sense). 

Even if you only eat meat, the excess proteins are converted into carbs *by your own body* before being metabolized.

In nature, even true carnivore species have double digit percentages of non-meat in their diet.