too much常用作副词或代词，也可以用作形容词修饰不可数名词。所以是Don't eat too much，

too many + 可数名词复数

eat too much前面可以填的有很多。可以加个主语。

例如：

I eat too much./He eat too much./She eat too much.意思是“我/他/她吃的很多”

也可以加上一些解释，组成长句子。例如：

Maybe I eat too much and that's what makes me dozy.

也许我吃得太多了，所以昏昏欲睡。

This is because people become so hungry at noon that they eat too much for lunch.

这是因为人们中午太饿,午饭吃得太多了。