One problem that people have is understanding what a portion is, because you say we should have this many servings of fruits and vegetables a day, we should have this many servings of that a day.

人类很难理解每餐食物摄入量这概念,因为假设,我们一天应该摄入一定份量的水果和蔬菜,各种食物每天都有一定摄入量

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选