And I believe that the grammar is no problem. My wife is always telling me: '多喝啤酒不健康‘. She never uses 很。If you don't use 很 it sounds more authoritative, like its a statement of fact. If you use 很, it sounds more like an opinion.

几个比较地道的说法: 多吃水果身体好。 多吃水果对身体好。 多吃水果，有益健康。(香港台湾等地常用)

一般可以说： 多吃水果会比较健康。 多吃水果对身体比较健康。

“多吃水果有益健康”-eating fruit is good for your health，“多吃水果身体好”-eating more fruit can better your body，“多吃水果对身体好”-eating more fruit is good for your body，“多吃水果让你健康”-eating more fruit makes you healthy."多吃水果健康" sounds strange,it lose some key parts that may not be supposed to be omited.（after "-" followed translation）

It's 6:47 in China, too early for Chinese people to answer your question, so I will try. If you have the 很 or don't have the 很 the meaning is slightly different. I believe that: 多吃水果健康 translates to 'Eating fruit is good for your health'. 多吃水果很健康 translates to 'Eating fruit is (very) healthy'. Happy to hear from native speakers what they think!