Suggest you buy this book dietetics teaching material, there is detailed introduction inside. 建议你买本书营养学教材，里面有具体的介绍。
Food composition studies are not only basic, but also essential for many purposes in nutrition, food science, and dietetics. 食物成分的研究在食品科学和人类营养学研究中既是应用基础、又是研究工具。