Net acid production, which is produced as intermediary or end products of the endogenous metabolism, consists of volatile acids and ifxed acid. It mainly comes from three sources:the metabolism of sulphur amino acids, the metabolism or ingestion of organic acids, and the metabolism of phosphate esters or dietary phosphoproteins. Net base production occurs mainly as a result of absorption of organic anions from the diet. Diet absorbed into the body will produce net acid or base, in order to maintain acid-base balance, the net acid or base will be neutralized by the buffer system or be excreted through lung and kidney. Because of the many reactions involved in the acid-base balance, we can’t measure the net endogenous acid production (NEAP) directly. Instead, the net acid excretion (NAE) assesses the acid-forming potential of the ingested diet based on its composition. So NAE can represent NEAP. However, NAE can’t be used to assess the acid-base balance of plasma.%体内代谢产生的净产酸（net acid production，NAP）分为挥发性酸和固定酸，主要来源于三种途径：含硫氨基酸的代谢、有机酸的吸收和代谢、磷脂和磷蛋白的代谢。净产碱（net base production，NBP）主要来源于有机阴离子的吸收。食物摄入体内后会产生净酸或净碱，为了维持体内的酸碱平衡，产生的净酸或净碱会被体内缓冲系统中和并经肺和肾排出体外。由于食物摄入体内后参与的代谢复杂，不能直接测量内源性净产酸（net endogenous acid production，NEAP），而酸排泄净值（net acid excretion，NAE）可根据食物成分来计算获得，故NEAP可用NAE来代表。虽然通过NAE可以计算食物的酸碱负荷，但其并不反映血浆酸碱平衡状态。
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