人类是食肉动物，还是食草动物？

Are human beings anatomically more similar to natural carnivores or to natural herbivores? Let’s find out….

• Intestinal tract length. Carnivorous animals have intestinal tracts that are 3-6x their body length, while herbivores have intestinal tracts 10-12x their body length. Human beings have the same intestinal tract ratio as herbivores.
• Stomach acidity. Carnivores’ stomachs are 20x more acidic than the stomachs of herbivores. Human stomach acidity matches that of herbivores.
• Saliva. The saliva of carnivores is acidic. The saliva of herbivores is alkaline, which helps pre-digest plant foods. Human saliva is alkaline.
• Shape of intestines. Carnivore bowels are smooth, shaped like a pipe, so meat passes through quickly — they don’t have bumps or pockets. Herbivore bowels are bumpy and pouch-like with lots of pockets, like a windy mountain road, so plant foods pass through slowly for optimal nutrient absorption. Human bowels have the same characteristics as those of herbivores.
• Fiber. Carnivores don’t require fiber to help move food through their short and smooth digestive tracts. Herbivores require dietary fiber to move food through their long and bumpy digestive tracts, to prevent the bowels from becoming clogged with rotting food. Humans have the same requirement as herbivores.
• Cholesterol. Cholesterol is not a problem for a carnivore’s digestive system. A carnivore such as a cat can handle a high-cholesterol diet without negative health consequences. A human cannot. Humans have zero dietary need for cholesterol because our bodies manufacture all we need. Cholesterol is only found in animal foods, never in plant foods. A plant-based diet is by definition cholesterol-free.
• Claws and teeth. Carnivores have claws, sharp front teeth capable of subduing prey, and no flat molars for chewing. Herbivores have no claws or sharp front teeth capable of subduing prey, but they have flat molars for chewing. Humans have the same characteristics as herbivores.

But aren’t humans anatomically suited to be omnivores?

Nope. We don’t anatomically match up with omnivorous animals anymore than we do with carnivorous ones. Omnivores are more similar to carnivores than they are to herbivores. For a more detailed summary table that compares the properties of carnivores, herbivores, and omnivores side by side, see this page:
Comparative Anatomy & Taxonomy

The link above also debunks the opportunistic feeder theory, which states that because humans can eat like omnivores, that we must therefore be omnivores. And this is of course false because mere behavior doesn’t indicate suitability. There are plenty of things we can do as a species that would threaten our survival if we all considered them suitable default behavior, such as shooting each other, lobbing hand grenades, or sending spam.