Phizzy is right on:
Carnivores evolved to be thus, it would take a million years, and lots of painful deaths, and a lot of genetic fiddling to get them to eat straw.
I have a lot of vegetarian and Vegan friends (remember I'm from the 60s generation). Not to cause an argument, but for many tens or hundreds of thousands of years man evolved into a carnivore. Why? Because it was a healthier diet for survival at the time, and still is.It will likely shift in a few centuries.
I don't really have to eat much veggies or carbs, though it may make me healthier due to the added vitamins and good contents. I also take good vitamins and "green" drinks. But IMHO, and experience having colitis, I have never had any problem with meat and never get sick. I do eat veggies but most of them I am allergic to unless they are cooked (citrus fruits are an exception - I have no problem with them). I do like most vegetables, but they give me infinitely more problems in digestion, heartburn, etc. than meat (not junk food meat but healthfully prepared - I can't eat any processed or even restaurant food due to the excess salt and other bogus ingredients like yeast extract). I must fix ALL my own food, which is unfortunately more expensive than junk food. Low salt, low in aggravating spices.
I also take high-quality probiotics because I have candida along with my colitis, allowing NO WHEAT, YEAST, SOY SAUCE or TOFU, or really anything fermented heavily, like strong cheese. All the things I love to eat (bread is #1).
This is not my choice or phiilosophy. When you are nauseating for three days and wishing you would die for relief of a tightly closed stomach (location of ulcer: near stomach) even water bloats me and will not eliminate during those times), you don't write scholarly papers on it. But if I follow my regiment (fix all my own meals, no packaged foods, pizza, or canned foods which ALL contain yeast extract, I am asymptomatic).
I often wonder just how much evolution is behind this. I first got the colitis about 20 years ago by taking massive doses of repeated antibiotics, which destroyed all bacteria in my stomach, good and bad.
Food for thought. :-))
Randy