In the view of Traditional Chinese Medicine, both food and medicine are composed of "qi" and "flavor," and their "qi" and "flavor" can only absorb the essence of heaven and earth when they are in season, that is, when their growth and maturation align with the solar terms.
There is a famous saying in the "Huangdi Neijing" (The Yellow Emperor's Inner Canon): "Sui Sui Bei Wu," which means to follow the natural yin-yang transformation to gather medicinal and food substances. Such substances, having absorbed the essence of heaven and earth, possess a rich and pure flavor and high nutritional value. Therefore, people should eat vegetables that are in season, and it is best to take wild herbs for medicinal purposes.
Animals and plants can only mature within a specific growth cycle, containing sufficient "qi" and "flavor" only then.
Vegetables that defy the natural laws of growth violate the pattern of spring birth, summer growth, autumn harvest, and winter storage, leading to an imbalance in their inherent cold or nature and a混乱 of their flavors. They become what is known as "vegetables in form only." Lacking the character of the season, they are merely an empty shell without their true substance. For example, cabbage in the summer may look good, but its flavor is far inferior to that of winter cabbage. Tomatoes in winter are often hard and tasteless. These off-season vegetables contain too many hormones, and long-term consumption is harmful to the human body rather than beneficial.
This is the essence of Confucius's famous saying: "Bu Shi, Bu Shi," which means, "Do not eat that which is not in season." In other words, try not to eat vegetables that are out of season.