Where are most poisons found? The answer is plants. When you think about all the food that you can eat the ones that have the most potential to poison you quickly or slowly are derived from plant sources. There must be a good reason why children need to be forced to eat vegetables. Maybe they are closer to their instincts, being so young, that they naturally and for good reason are repelled by vegetables – especially green leafy ones. Apparently it has never really been conclusively proven that eating lots of fruit and vegetables is good for you. Most vegetable matter is not designed to be a food and indeed some plants actively discourage being food items by being poisonous. Some animals manage to adapt to poisons, probably at huge initial cost, finding a niche on a poisonous plant. Monarch caterpillars come to mind here where they live on the poisonous Milkweed and in doing so become poisonous themselves.
Common food like potatoes, beans, plums, rhubarb and tomatoes have serious poisons in them. Most seeds are poisonous – after all there is no benefit to a plant to have its seeds eaten and absorbed into animals. Seeds that pass right through the gut are probably a good idea for geographical distribution so most plants would have an interest in protecting their seeds. Some develop the use of poisons to achieve this. Some develop hard outer shells.
The only real foods are milk, egg yokes and animal fat. These are actually designed to be foods for animals. Cultures have been known to exist that ate an almost 100% animal product diet and thrived. Some African tribe ate mostly fresh blood and milk and Eskimos ate mostly blubber without ill-effect and stayed lean. Nature has spent millions of years developing these foods yet in recent times they have been demonised. Instead of eating nutritious meat, eggs and dairy products people are eating masses of grains and inedible leafy vegetables thinking that it is healthy.
Consider whole grain breads – better for you because more of it passes straight through you. Tells you something about how good it is for you don’t you think?