There are historical and scientific records that proof that we have had an omnivore diet for most of our history.
Extracts from Nutrition and Health in Human, Evolution–Past to Present, PubMed:
"The diet of prehistoric humans was determined by the seasons, the availability of resources, climatic conditions, and the biotope they lived in. With a lifestyle dominated by gathering, the available food consisted primarily of plants (80%) such as leafy greens, sweet grasses, nuts, seeds, tubers, berries, roots, fruits, and pulses as well as animal proteins from wild animals and fish (20%)."
"While our earliest ancestors were more or less herbivores by nature, as indicated by their anatomy and physiology, Homo later evolved into an omnivorous species."
"In principle, humans are omnivores by biological design. Unlike other species, they are food generalists, which means that they do not make any specific demands on their diet. This allows them to survive under diverse conditions in almost all geographical regions by consuming a wide range of organic substances provided by the animal and plant worlds."
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9460423/
We have had plenty of time to adapt to eating plants. We also rely on the microbiome to digest plants.
The gut microbiome refers to all the organisms, amongh which bacteria, that live input colon. Fiber is the preferred food of the gut bacteria and fiber can only be found in plants.
If you are interested in learning more about the microbiome, here are a few podcasts:
https://www.richroll.com/podcast/will-bulsiewicz-680/
https://shows.acast.com/thehappypear/episodes/dr-alan-desmond
https://www.richroll.com/podcast/robynne-chutkan-714/
