eat为动词,eating为动名词,代表饮食、吃饭,为泛指一般良好的饮食习惯用good diet或者good eating habits所以可译为The sports stars have a good eating habit或者The sports stars have good eating habits或 The sports stars have a good diet.
因为饮食在这里不是做谓语,谓语是have,饮食是习惯的定语,所以不能用动词原型而要用动名词来修饰习惯