JA RULE LEAP YEAR BIRTHDAY BEHIND BARS... JA MAICAN PATTIES, ANYONE?

It's the first time in four years Ja Rule can celebrate his real birthday -- February 29th -- but despite being stuck behind bars, Ja won't go hungry ... and we got the rapper's 2,500-calorie prison birthday menu to prove it.

According to the "heart healthy menu" at the NY State prison where Ja is currently serving a two-year sentence for gun possession -- JR can look forward to some delicious corn flakes in the morning, Jamaican patties for lunch, and turkey stew for dinner.

According to the menu, the entire day's worth of food totals between 2,500-2,800 calories -- significantly more than the USDA 2,000 calorie guidelines.

FYI -- we don't know how he did it, but Ja released his 7th studio album yesterday ... all while under lock and key.