Brandi Mallory died from complications due to obesity -- this according to her official autopsy report.

TMZ obtained the document from the Fulton County Medical Examiner, citing the "Extreme Weight Loss" star's weight, an enlarged heart, and some elevated blood indicators suggestive of prediabetes all as factors in her overall health.

The paperwork says there was no sign of a recent injury and there was no reason to suspect foul play either. The report does note there were trace amounts of marijuana and alcohol in her system ... but the coroner says neither played a role in her death.

Here's how they put it in the autopsy ... "It is my opinion that Brandi E. Mallory died of complications of obesity was considered a significant condition contributing to the death." It also lists her death as natural when it comes to the manner.

TMZ broke the story ... Mallory was found dead in an Atlanta strip mall parking lot after being seen entering her car the night before. A concerned bystander called 911 and said he suspected there was a body in the car, as he noticed it hadn't moved for a long time.

Mallory competed on Season 4 of the ABC series back in 2014, and had been involved with the program as recently as 2018.

She was only 40.

RIP