What are you going to do if you wreck your health? An unbalanced diet is the source of all illness, you know.
Literal
Body break-[if-たら] what-do-[explanatory-んだ]. Unbalanced meal [topic-は], ten-thousand-illness [possessive-の] source is-[masculine-ぞ].
The casual speech drops ~を after 体 (体壊す instead of 体を壊す), a typical informal elision. ~んだ at the end of a question frames it as 'what do you (think you're) going to do?' — confrontational rather than neutral. 万病の元 ('root of ten-thousand illnesses') is a traditional saying for 'the cause of every ailment'; 万 here is rhetorical ('all'). ~ぞ is a masculine/assertive sentence-ender used for driving a point home. アンバランス is a katakana loanword (from English 'unbalanced') behaving as a na-adjective.