Being a substance that is required for normal functioning but does not need to be included in the diet because of the body's ability to synthesize it from other nutrients.
（氨基酸）非必需的是正常的运转所需要的物质的，但因为机体有从其它营养成分合成它的能力，因此不需要被包括在日常的食物中的
The two elements are synthesized by a chemical process.
这两种元素已经化学合成.
