Why can certain animals thrive only a certain type of vegetation while we need tons of variety? What if a person just ate quinoa, berries, kale and some eggs? (just a random example) Would they eventually become malnourished? Did early humans consume all types of vegetation or just a few things, etc???
I gravitate to examples of evolution that prove humans and animals can eventually learn to survive on anything.
However, I like basic physiology that proves optimal health equals that we need complex carbs to be anerobic, we need fats to be aerobic, and we need protiens to keep our bodies strong and healthy.
Without carbs in the diet it will lead to euphoria and brain damage, and no energy. Lack of fats and carbs will actually make the body store more fat and people will have difficulty losing fat, although they will lose water weight. Lack of protien has many serious side effects.
Howevre people have been known to survive extremely without on or another, but it doesn't mean they will be in optimal health.
Survival doesn't necessarily mean being healthy, but the body is able to literally survive on anything or even
nothing for a very long time, the only exception being that we always need
water.
We've adapted to be able to withstand extreme starvation, and the ability to live without important nutrients in our diets.
People quickly adapted to be able to eat modern foods, while others who did not evolutionize as fast have problems with modern foods.
The inuit people had abnormally large livers, and this was perfectly natural for them because they had to adapt to their environment of very little vegetation and a diet strictly of meats, mostly raw. If just anybody were to start eating that way suddenly, it could make them very sick, like in cases of people suddenly following atkins diets, because their organs have not yet had time to change or adjust to it, and their bodies are not accustom to that much meat in a diet.
But given time, people can literally force their bodies to adjust to eating anything. That doesn't mean they'll be healthy though.
First nations people here ate a huge variety of things and were never starving even during the winter, because this land was called the Land of Plenty or in the coast salish language, K'omoks. An example of all the wild edibles here are a huge amount of berries, tree barks, trees, saps and syrups, roots, insects, a whole bunch of different plants and fruits, mushrooms. Because this is an island surrounded by ocean and full of rivers and lakes there was/is a neverending supply of salmon, trout, other types of fish, whale, seal, and other sea creatures and seaweeds. Also they feasted on reptiles that live here like frogs and snakes. Wild game has always existed here and were not "brought" here like some islands, because this island is surrounded by a bunch of tiny islands that are swimming distance away, that are surrounded by more tiny islands, so you can literally kayak across to many small islands until you get to the mainland but there are dangerous currents in some places, so we always had elk, beaver, black bears, grizzly bears, deer, cougars and wolves and much more also they ate tons of birds and eggs. Most of these things are also available in the winter. This would be a very easy place to eat a wild edible diet. I'm thinking of starting that someday, but man it would be a lot of work to go collect wild edibles and there's a lot here, but there are also indenticle poisonous things so you have to be sure.