Question

为什么Eating fruit and vegetables is good for your healthy里要用eating？

Answer 1

Eating fruit and vegetables这个短语才是主语。短语作主语时只能用to do或doing。再详细的一点就是动词带一个动作或带一个名词必须是to do sth或doing sth，然后再跟谓语（在这个句子里是is）。
还有，你的句子应该是Eating fruits and vegetables is good for your health。

Answer 2

因为动词放在开头作主语时要用ing形式。变成动名词。 嘻嘻.

Answer 3

动词放句首要加ing变成动名词。。。这是固定用法。。。记住吧。。。

Answer 4

【Eating】 is used as a subject.主词
eat + ing change into a noun名词