Oh the irony of the scheduling. Just before this eye-opening and sometimes grotesque documentary, How To Look Good Naked was broadcast. Straight afterwards came the tale of Renee Williams – at 64 stone, the world's heaviest woman. Even the undisputed and fantastic powers of Gok Wan couldn't help this woman – bedridden and unable to function, Renee needed more than just an arm round her and some self-improvement techniques.

Let's get this straight. Renee Williams is a big woman. A massive woman, who looks like a human cloud. The question asked during this film was whether America's alarming trend towards morbid obesity is a self-inflicted condition or a genuine disease. After watching it (and wishing I hadn't eaten so much chocolate over Christmas) I have to say it's probably a bit of both.

We meet Renee. Out of the mounds of enveloping flab, Renee's little head explains that she's always been overweight. At 29-years-old she's at the point of no return, and has campaigned to have gastric bypass surgery for 12 years.

Telling her story, the 64-stone woman was keen to dispel some myths – fat people don't smell that bad and that fat people have feelings too. Renee certainly does. She wants a better life for herself, and wants to spend quality time with her children. At the moment, she's propped up in this weird bed, which looks like a huge car seat. She can't turn over and cannot move.

So far so documentary-by-numbers. Renee continues to tell us that she was 40-stone at 26, but a car accident left her bedridden and the weight started to increase, until she couldn't move. Her eating spiralled out of control and within three years she had put on another 20 stone. Yikes.

Described as 'super morbidly obese' experts give her one year to live unless she has this operation. We're introduced to her daughters for full emotional impact, and then to someone who had the (successful) surgery and changed her life around.

We followed Renee as she went in to hospital, and I was, in accordance with these by-the-numbers docs, fully expecting a happy ending. It didn't have one – Renee died soon after the operation.

I wasn't expecting that and it shocked me. Because of the way the film had been set-up, I was certain that Renee would survive the surgery and begin to walk again. The documentary was sympathetic, and followed the usual narrative that human freakshow shows normally do. But Renee died and I felt sorry for her. She had to be lowered into her grave via a winch. It was pretty grim stuff.

I often wonder about these body issue docs. Are they genuinely made to raise awareness to a particular condition, or are they designed to make us point and stare in a grotesque sort of voyeurism? As for obesity, I believe the causes are many – rock-bottom self esteem, an abundance of crap to eat, and a society that encourages eating said crap. It's a shame Renee couldn't be saved or feel strong enough to help herself when she had the chance, because her daughters deserve a mother.