Lyoto Machida -- The Secret To The Perfect Brazilian Butt Is ...

UFC badass Lyoto Machida is about to get to the bottom of a mystery -- a bottom mystery -- 'cause the pro face breaker just told TMZ Sports why women in his native Brazil have such nice ... assets.

Machida was out in Beverly Hills with his smokin' hot wife when our camera guy asked the question that women all over the world want to know -- how do Brazilian chicks get their mystical booty powers???

Check the video -- Machida gives our camera guy two reasons Brazilian chicks are so bootylicious.