Hello
Thanks for query.
You have not mentioned your age in your query.
Based on the 
Ultrasound Scan findings reported I would say that you have Benign Enlargement of Prostate with significant post void residue .
The answers to your queries are as folow 
1) You have benign enlargement of prostate which is common after the age of 55 years.
2) It is the ageing process and not the disease and 50-60% of males get it 
with advanced ageing .
3) Treatment depends upon the severity of obstructive urinary symptoms like frequency ,urgency,urine flow and nocturnal urinary frequency.
It is decided by the 
Urologist after doing following basic test like 1)Uroflowmetry .
2) Post Void Residue 
3) AUA Symptoms score .
4 ) Diet has no role to play as for as treatment is concerned.
It can be managed either by medicine like Tomsulosin and 
Dutasteride or and Endoscopic resection of 
enlarged prostate (TURP).
Consult qualified Urologist for detail investigations and further treatment.
Dr.Patil.