AFTAB Ali is only 31, but spends his days in a chair in his living room being cared for by his wife, Millie, 21.

At 39 stone, he is super-morbidly obese and cannot easily venture into the outside world. "I don't know much about what is happening out there," he says ­wistfully, looking out the window of his home.

But with the help of a personal trainer and psychological support he has lost six stones, enabling the young couple - who met on the ­internet - to enjoy their first-ever date in a restaurant.

Ali's story was highlighted last week in a Channel 4 documentary "Shut-Ins: Britain's Fattest People" which documented the struggles of the estimated 50,000 people in the UK who remain trapped inside their homes due to their size.

The popularity of TV programmes focusing on issue of weight, it seems, shows no sign of abating. In fact it is accelerating, and becoming one of 2015's entertainment trends.

Also hitting the schedule days into the new year has been Channel 4's Weighing Up The Enemy, which pits two overweight contenders against each other to try to spur them on into losing the most body fat to win cash.

Meanwhile, attempts by ­controversial TV personality Katie Hopkins to gain and lose a large amount of weight to show how being fat is just an "excuse" have also been the subject of a recent documentary.

It was more than a decade ago that NBC's The Biggest Loser, in which contestants compete to lose the most weight, was first broadcast in the USA, spawning a whole new genre of television as well as ­numerous versions of the show worldwide.

The race to come up with twists on the winning TV formula has since resulted in shows ranging from using hidden cameras to capture sneaky chocolate-bar eating to showing overweight dogs and their owners trying to get trimmer together.

Keri Lewis Brown, ­managing director of K7 Media, which provides insights on global trends to ­broadcasters, said the shows about weight appealed particularly to ­audiences after the festive season.

"I think it resonates with how we all feel at this time of year and it does make you feel good about ­yourself if other people are worse than you are," she said.

"Then you have got the classic television thing of transformation, so people are watching something which is like a health makeover."

Lewis Brown said the shows are an example of a type of TV show which endures because audiences like to watch "effort and passion" - qualities which an ITV study on 21st-century storytelling found were "possibly the only unifying values audiences can all agree on".

"We call them effort shows," Lewis Brown said. "It is ordinary people doing an extreme thing - so watching a very fat person doing a boot camp or trying to train for a marathon, you can't help but admire them. A lot of these weight-loss shows do involve people that have never exercised before trying to for the first time - which makes quite good television."

Unsurprisingly, the obsession with TV programmes around weight mirrors the trend of the nation's expanding waistlines. Last week, a report from the Scottish Parliament Information Centre (SPICe) revealed the total economic cost of the nation's weight problem could be as much as £4.6 billion a year.

The stark reality is that being of a healthy weight is now in the ­minority, with 64% of adults in ­Scotland falling into the category of being overweight or obese.

Dietitian Lucy Jones of the British Dietetic Association, who advised on Weighing Up The Enemy, said the programmes showed no signs of losing popularity.

"As a nation we are obsessed with our weight and our health and our diet and everything to do with it," she said. "TV production companies and channels are very shrewd and they play to what people want."

Jones said the programmes can help motivate viewers to lose weight, although she pointed out this is not their primary focus.

"Generally they are entertainment programmes, but it is nice to get health messages out in an ­accessible way to a wider proportion of the population," she said.

BUT not all the TV shows give a positive view of the problem. A Channel 5 documentary, Benefits: Too Fat to Work, broadcast last week, prompted scathing headlines about a couple with a combined weight of 54 stones. Stephen Beer and wife Michelle were criticised for spending £3000 on their wedding while receiving benefits.

A new two-part series for the TLC television network shows Katie Hopkins' efforts to gain and lose three stones to prove obesity is a choice. Her comments have included: "All fat people want is an excuse … Nobody's forcing them to shovel food in their faces."

Jones said: "There are two tales to this story - and the other side is that we still live in an environment where there is a lot of stigma attached to being obese, despite it being a very common problem."

She added that only focusing on the most extreme cases risked changing perceptions of what obesity is.

"We know the majority of people who are overweight and obese underestimate how much they weigh, or think they aren't in this category of obesity, as when they hear of obesity they think of programmes like Shut-Ins or Britain's Fattest Man and they can't relate to that," she said.

"But obesity is a much wider ­problem and affects anyone with a BMI above 30." A healthy BMI or body mass index, a figure worked out from weight, height and gender, is between 18 and 25.

Professor David Haslam, chair of the National Obesity Forum, said the "unquenchable thirst" for programmes about obesity helped to keep the issue in the public eye.

But he added: "There are ­responsible ones and irresponsible ones and the ones that do recreate the 'freak show' do need to be toned down and lose that element of circus.

"It can be voyeuristic - looking and marvelling at it [obesity] and I am certainly not very happy about that kind of programme any more than I would be if the circus freak show made a comeback."

Susan Ringwood, chief executive of eating disorders charity Beat, said programmes on obesity often focus too much on physical health, rather than the emotional issues which can trigger eating problems.

"Recent research suggests that almost half of the population ­medically classified as obese may in fact use food as a way of managing their emotions," she said.

"Diets don't work, and this can add to an individual's sense of failure and helplessness.

"Having an emotionally healthy relationship with food is an ­essential part of maintaining a healthy weight, and psychological support is often required."

But Dr Abigael San, a ­chartered clinical psychologist who has advised on programmes including Supersize vs Superskinny and Shut-Ins, said those who volunteer for the TV shows often successfully make changes which can inspire others.

"It gives you an example of how it can work," she said. "Often the changes people make - as with many things - are simple, but it is a case of actually doing it. They are not doing anything complicated that viewers couldn't be doing themselves."