'My 600-lb Life' Star Latonya Pottain Dead at 40

11:20 AM PT -- TMZ obtained the coroner's report from the Parish of Natchitoches ... Latonya Pottain died from "acute on chronic congestive heart failure." No autopsy will be performed, since the death is considered due to natural causes. Pottain was taken from an inpatient medial rehab facility at the time of her death.

Latonya Pottain -- best known for being featured on the reality TV show "My 600-lb Life" -- has died of natural causes in Louisiana, TMZ has learned.

Pottain passed away Saturday night at CHRISTUS Highland Medical Center in Shreveport, LA, according to the Natchitoches Parish Coroner’s Office. The coroner tells us the preliminary investigation found Pottain died from congestive heart failure.

Pottain's brother also told TMZ  ... family members visited Latonya at her home Saturday morning, and they noticed she was having trouble breathing. Her brother said Pottain told them she was extremely uncomfortable. On top of that, she didn't look well.

Her brother said the family got a call later from a nurse who told them Latonya called an ambulance to bring her to the hospital because she was going into cardiac arrest, which led to her death.

As you may know, Pottain appeared on Season 11 of "My 600-lb Life," and the show tracked her journey to lose weight.

At one point, Dr. Younan Nowzaradan, AKA Dr. Now, broke the sad news to Latonya that he couldn't do anything for her because she failed to stay on her weight-loss program.

In fact, every time Pottain met with Dr. Now, she learned she had gained weight instead of shedding pounds. The only time she ever lost weight was when she was previously hospitalized with heart issues.

Pottain died Saturday at age 40.