由于使用火和磨石，大量谷物被消耗并转化为主食。

With the use of fire and grindstones, large amounts of cereals were consumed and transformed into staple foods.

youdao

youdao

这种鱼以浮游生物为主食。

The fish live on the plankton.

《柯林斯英汉双解大词典》

Now the fact that people were so reliant on certain foods led to deficiencies of certain nutrients, so people that were dependent on a rice based diet tended to have problems with deficiencies in protein, Vitamin A, and thiamine.

人们过于依赖某些特定的食物,导致了某些营养元素的匮乏,因此,以米饭为主食的人,很可能缺少蛋白质,维生素A和维生素B1

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选