I hate to say it and know I'm going to get a lot of flack especially from vegans, which I have a lot of respect for from an ethical standpoint. Realize that my critic comes purely from a scientific and evolutionary standpoint. So here goes:

The growing body of evidence is that humans are not evolutionary cut out to eat plants to the level we do today. This article somewhat reinforces that point. The reason we stand out from other apes is likely the fact that we diverged to become a carnivorous ape roughly 3 million years ago, leading to our massive brain size as well as other abilities.

Evidence:

-Bone analysis of our ancestors indicates they were primarily carnivorous over the last 3 million years before the advent of agriculture. Probably only 10-15% of our food was plant based. That puts us in the same place as wolves and bears in the food chain.

-Humans require vitamin B12 to thrive, which can only come from animal sources or certain bacteria (vegans must supplement their diet).

-Your gut structure closely matches that of a carnivore, not a herbivore. Just because you can tolerate plants doesn't mean you should.

-Humans are the only living primate adapted for endurance running. This was likely to out last running prey.

-The healthiest populations on the planet are those that still maintain hunter gatherer lifestyles with no spill over of modern food. Plenty of anthropological field research pointing this out.

-Humans are among the few mammals that don't produce vitamin C naturally. A sign we primarily got this from eating animal organs since access to citrus fruit is seasonal.

-The prevailing theory is that our large brain capacity came along with the fact that we high and easy to access sources of Omega-3 fats. Fish or large game primarily. There is also a related theory that we were primarily aquatic apes, since we also have a lot of adaptations for water.

-Tapeworms: Without infecting a human host, at least four species of tapeworm would be unable to reproduce. Humans are a definitive host for them. The only other mammals to be definitive hosts for tapeworms are carnivores like lions and hyenas.

-Smaller canine teeth compared to great apes indicates they were less used for male to male conflict like we see in great apes, and more so used for meat eating. This falls in line with the time frame we see a switch to carnivore.

-Interestingly, we have very powerful livers for detoxification and a very strong ability to smell rot, decay and decomposition relative to other animals. This suggests we may have evolved first as scavengers then grew into hunting more.

-Egyptian mummies are the first times we see heart disease and tooth decay, as well as less robust skeletal features. In fact anthropologist recognize pre and post agricultural specimens pretty easily.

As I read this article I can only see another drop in the bucket that reinforces the point: Humans are not meant eat this many plant. We keep fooling ourselves with this notion that hormetic responses are "good for you" and "toughen you up". Its like telling a wolf that eating a salad is "good for you". Sure you can't feed the planet without agriculture nor can we feasibly go back to being hunter gatherers, and the vegans do hold the ethical high ground. However if the question is simply: "What are humans evolved to eat." The answer is right in our face and our modern culture hates to accept it: meat. Primarily nose to tail. Vegan diets tend to be healthy in the short term especially when you switch from the Standard American Diet, and deleterious in the long term without serious hacks to make up for nutrient deficiencies and the accumulation of plant toxins. Look at the high rates of infertility in vegan communities, the likely culprit is plant toxin accumulation and malnutrition. Especially when you look at the research involving the long term accumulation of plant oxylates.