WorldStarHipHop Founder On Weight Loss Kick Before Sudden Death (UPDATE)

4:05 PM PT -- Q did die from a heart attack, according to the San Diego County Coroner. Autopsy results also list "obesity" as a contributing condition. He failed to respond to CPR, and was pronounced dead on the scene.

WorldStarHipHop founder Lee O'Denat -- better known as "Q" -- had been on a fierce path to slim down in the weeks leading up to his death.

We're told Q, the face of WorldStar, had been going HAM in the gym and on the treadmill -- sometimes at 5 AM. People close to him say he was over 300 lbs. at his heaviest, but had been trying to shed weight to look his best for his new MTV reality show ... slated to premiere in the Spring.

The show revolved around 43-year-old Q, his website's crazy videos and celebrity guest appearances. We're told Q had been telling friends how insanely busy he'd been juggling the show and his new gym life.

TMZ broke the story, Q died in his sleep Monday night. An autopsy is set for Tuesday.