The mobile khanates are documented eating horse meat and dairy products along their vast nomadic tracts

Renowned for their ability to ride for days and immediately go into battle, this maps to what we understand about modern carnivore - eating only when necessary, skipping meals, very high levels of energy speak to a fat based metabolism

Obviously the Mongols were not exclusive carnivores - they were opportunistic

https://www.historyonthenet.com/what-did-the-mongols-eat

Farming was not possible for the most part, so the most prominent foods in the Mongol diet were meat and milk products such as cheese and yogurt. The Mongols were a nomadic, pastoral culture and they prized their animals: horses, sheep, camels, cattle and goats. As their herds ate up the grass, the Mongols would pack up their gers, tent-like dwellings they lived in, and move their herds to fresher pastures.

Thus, their food groups were predominantly milk products and a variety of meats. While the Mongols appreciated milk products, they didn’t drink fresh milk; instead they fermented milk from mares, making an alcoholic drink known as airag or kumiss. After women finished milking the cattle, goats and sheep, they would process the milk into milk curds, yogurts and airag. The usual beverages were salted tea and airag, fermented mare’s milk.

There are curious theories that the Mongolian decline coincided with a change in their diet https://afe.easia.columbia.edu/mongols/pastoral/masson_smith.pdf

What other famous carnivore civilizations are there?