There is a cloud in the article "The Method of Storing Qi in the Yellow Emperor's Internal Classic": "Five grains are for nourishment, five fruits are for help, five animals are for benefit, and five dishes are for filling."
The five-grain regimen is the "five grains for nourishment" in Huangdi Neijing, that is, the so-called "five grains" refer to five food crops: rice, wheat, millet, millet and rice.
Huangdi Neijing is one of the four classic works of China's traditional medicine. As the earliest medical work in China, it provides us with the earliest and most comprehensive dietary guide in the world: to eat miscellaneous and comprehensive, but also to have a distinction between primary and secondary.
Rice, millet, millet, wheat, rice and hemp were the main crops at that time. The so-called grain refers to these crops, or five of these six crops. However, with the development of social economy and agricultural production, the concept of five grains is constantly evolving. Now the so-called grain is actually just a general term for food crops, or refers to food crops in general.