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"Sihui Tiaoshen" (Regulating the Spirit according to the Four Qi) in the *Huangdi Neijing* (Yellow Emperor's Inner Canon) is the foundation of health preservation. The five grains serve as nourishment, the five vegetables as supplementation, the five fruits as assistance, and the five meats as benefit. Dietary intake should be regulated and must not be excessive. Excessive eating leads to the hazard of excessiveness in specific qualities.

Therefore, consuming too much salty food causes blood vessels to coagulate and stagnate, resulting in changes in complexion; consuming too much bitter food causes the skin to wither and hair to fall out; consuming too much pungent food causes tendons to become tight and nails to wither; consuming too much sour food causes flesh to thicken and callous while lips peel; consuming too much sweet food causes bone pain and hair loss. These are the injuries caused by the five flavors. However, what humans rely on for life is grain. Among the natures of all things, none is more central, balanced, and peaceful than grain. Thus, even if a person lives to a hundred years, they will never tire of regularly eating grain. In ancient times, the method for treating diseases was to use the flavor of grains for convalescence after the illness had passed; it was never the case that峻补 (potent tonification) was used after illness. Zhang Zhongjing is the ancestor of formula creation. Observing his works *Shanghan Lun* (Treatise on Cold Pathogenic Diseases) and *Jingui Yaolue* (Essential Prescriptions from the Golden Cabinet), one finds that his formulas were primarily for treating diseases, with very few being tonifying formulas. Among later scholars, only Zhang Zihe grasped this principle: after the disease was eliminated, he taught people to use millet gruel for recovery, which did not contradict the purport of the *Neijing*. The prevalence of tonifying formulas, however, began with Zhang Jingyue and Zhao Yangkui, who frequently employed Ginseng Radix et Rhizoma (Renshen, 人参), Angelicae Sinensis Radix (Danggui, 当归), and Rehmanniae Radix (Dihuang, 地黄). Xue Liza followed their example. Later generations, merely awed by their reputations, accepted this as truth. Those who imitated them harmed countless people. Examining their medical records, one sees that Bu Zhong Yi Qi Tang (Tonify the Middle and Augment the Qi Decoction), Xiao Yao San (Free and Easy Wanderer Powder), and Gui Pi Tang (Restore the Spleen Decoction) were used indiscriminately to treat all diseases, with few other formulas adopted. This alone makes it clear. Generally speaking, the four seasonal qi of wind, cold, summer heat, and dampness, when invading humans, are termed pathogenic qi. Humans exist within the intersection of qi; how can they avoid it? Wind injures Wei Qi (Defensive Qi); cold injures Ying Qi (Nutritive Qi); summer heat injures Yuan Qi (Primary Qi); dampness injures the skin, flesh, tendons, and bones, and internally damages the Spleen and Stomach. This is how the four qi injure humans. When affecting the exterior, symptoms include aversion to cold and fever; when affecting the interior, symptoms include fatigue and heaviness in the four limbs. These resemble the deficiency patterns of internal injury, analogous to the dimming of a lamp due to soot accumulation, as discussed in detail previously. If external pathogens are vigorous, or if the illness has just resolved but pathogens remain, administering tonifying formulas by mistake will inevitably cause pathogens and healthy qi to entangle each other, like oil mixing into flour, making them impossible to separate, thereby leading to lifelong disease. This is truly lamentable. Those with insight should take heed of this, hence the saying "not taking medicine constitutes the highest level of medicine." It is better to rely on grain for nourishment, which saves costs and avoids adverse effects.