Plant oils, proteins and fats.
We digest meat much more slowly, it does not mean we cannot do a half job of it. We also break down coal if left long enough time. Omnivore means a bring that can eat LOTS of things.
We don't die overnight, but it's common knowledge that meat eaters get much higher rates of disease, from breast and colon cancer to prostate cancer and heart disease. It's fact.
We also have the ability in inhale nicotine in cigarettes, and our lungs still absorb the smoke.
We've been smoking an beating women and keeping slaves as long as there has been human civilizations. Does this mean it's a good habit?
No. And as soon as we realise, through social and biological science that this is wrong,= eg, animals feel the same as us, they communicate in soundwaves beneath the sea, cows emote, women can think just as quickly as men, slaves are humans too, it's time to evolve in the same way and stop doing those thing you know ( that you didn't used to) cause pain and are a backward caveman way of thinking.
If you don't KNOW women are the same as men, then how can you begin to treat them the same. Now we know we're of the same intellectual capacoty, men and women, we do our lives acoordingly differently. But until very recently, people really did think women and men were different. that slaves were not human, that black and white people were different etc.
Just because this has been done for centuries does not mean it is a good thing once you discover the science behind it.
Furthermore, there have been vegan and vegetarian communities for milenia.
VEgetarian and vegan communities- Hindus, Jain, Ahisma, these are COMMUNITIES which have been veg/an for a long long time. Thousands of years.