Mark Twain hit the basic problem with diets perfectly with,
“The only way to keep your health is to eat what you don’t want, drink what you don’t like, and do what you’d rather not.”
Wikipedia has a List of 100 Diets which will be the basic source for this post. We humans have the natural ability to eat and digest almost anything that other primates can eat. Gorillas eat lots of greens and little of anything else. I haven’t heard of anyone who eats a wild gorilla’s diet but the link above has gorillas in zoos eating supposedly healthy American diets and getting obese, diabetic and suffering from heart disease. Probably humans could eat gorillas’ diet but they probably don’t or the gorillas would have been driven to extinction by human encroachment on their living areas. Probably the same can be said for chimpanzees, bonobos and other primates’ food staples and natural habitats. Humans don’t eat those animals’ food because it requires more effort to harvest and/or digest those foods than it is worth for us. With the exception of fish, it appears to be more efficient for humans to grow most of their food rather than to hunt or gather it from natural sources.
We have genetically engineered natural foods for thousands of years to be domesticated for farming and to satisfy our particular human digestive abilities, nutritional needs, and taste preferences. The proof that farming works to our benefit is that for tens of thousands of years our wild human population was less than seven million and now it is over seven billion. That is, the Earth is now sustaining a thousand times more human beings using our modern industrialized farming techniques than it did when we were using hunter-gatherer pre-industrialized-farming techniques.
Much of our modern food productivity is based on one-time-use fossil fuels made of stored sun energy so that our large population isn’t sustainable unless other ways of harvesting the sun’s energy are developed. We are quite resourceful as a species so those necessary new techniques will probably come into existence. The population theorist Thomas Malthus wrote back in the year 1800 that our human population had reached its absolute limit, and indeed it had with the farming technology available at that time. However, since his book on the theory of population was published, we have gone from less than a billion people to seven and a half billion.
With the current CRISPR technology, it is probable that we will modify the DNA of desert and tropical plants to produce food usable by humans. It may be possible to create new food types that can be grown in currently sterile areas. Our present population may not be sustainable with our current technology but it may double within a hundred years with what we will probably bring into existence.
As amazing as the last hundred years have been, the next hundred years will probably be even more astonishing.