A nutrient is considered a substance within the food, that's when it digests it, absorbs, promotes some bodily function, so that it has some metabolic health value when people consume it.

营养素是包含在食物中的物质,由人体消化,吸收,推动身体机能,食品必须具有值得人类去代谢的健康价值

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选