How to use 越 ... 越 structure

Sentences 1-5 share the same meaning of 越 ... 越, means the more the action you do (吃水果in this case), the result (健康 in this case) you will get. Literally means "the more the fruits you eat, the healthier the body will become". Although all the sentences have got the structure slightly different, grammatically they are not wrong and can be understood in the communication in conveying the meaning of the more the fruits you eat, the healthier the body will become.

Firstly,吃越多水果，身体越健康。is not correct from the point of view of grammar. From the options you gave, 2 and 3 are correct.
Then I'll tell you 3 uses of this structure.
No. 1 越+v.+越+adj. (attention: there's only one single Subject),means "the action of sb./sth. is becoming more and more ..."
e.g.他越跑越快。He is running faster and faster.
小明越长越高了。Xiaoming is growing taller and taller.
我看着他们越走越远。I watched them walking away further and further.

No.2 there're 2 different Subjects. S1+越+v1, S2+越+v2. the 1st part is the reason that affects the result of the 2nd part.
e.g.青春期的孩子，家长越说，他们越不听。For teenagers, the more their parents talk (demand), the less they will listen to.
你越解释，他越生气。The more you explain, the angrier he will be.
雨越下越大，路上的人也越来越少。The rain is getting heavier and heavier, and there are fewer and fewer people on the road.

No.3 v1+得+越+adj1,v2+得+越+adj2
e.g.书读得越多，懂得也越多。The more you read, the more you know.
医生告诉我，生病后休息得越多，身体就好得越快。The doctor told me that the more I rest after being sick, the quicker my body will recover.

HOPE MY COMMENTS CAN HELP

你的身体吃越多越健康。