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Grains are grass seeds. The grains of today are rather tall, but they're huge compared to the seeds from which they're developed. Grains have been cultivated and eaten humans for only about 8,000 years.

In nature we did not eat grains or grass seeds. We did not develop any gathering or digestive equipment for grains. Natural grain eaters must be able to efficiently gather, grind and digest grains. Humans fail on all counts. Our teeth handle grains poorly. In fact, humans refuse to chew tasteless and hard grains. Even so, humans, not being starch eaters, cannot digest more than a handful of grains, if that much. True starch eaters secrete a plethora of starch-splitting enzymes in copious amounts. Humans secrete one starch-splitting enzyme, salivary amylase (ptyalin) which is quickly exhausted. After a mouthful or two of starch, the eater palls and stops.

Nope, we're not grain eaters. The way we do eat grains by mechanical gathering, refining, cooking, etc. makes them palatable but more pathogenic.