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?
I think the only other famed civilisation that ate only meat was the American plains Indians who ate bison and were only defeated by the destruction of the buffalo (bison) herds.
Those people were described as more magnificent that European nobles in their finery. Now they’re less healthy than European Americans, as they eat modern foods.
Indigenous Australians too ate little other than meat and insects. Australia has so few native plants that are edible, and most of those are in the tropics, but the British invasion of Australia was only 200 years ago, they had rifles and the Indigenous Australians were in the stone age. Paintings and drawings of Aboriginal men from the early days of British rule show they were tall men of impressive physique.
The Mongols were lucky that the people they were fighting didn’t have guns yet, back when being stronger and taller mattered.
Listening to Dan Carlin’s hardcore history, the Mongols were extremely renowned. Whether that was based on their diet, or just myth, it’s hard to say at this point. But there’s something there