Why The Biggest Loser contestants gain back their weight.

The physical transformation experienced by contestants on The Biggest Loser is nothing short of dramatic.

In a matter of months, their diet and levels of physical exercise are completely overhauled, generally resulting in the loss of a large proportion of their body weight (and many, many tears shed against a heart-wrenching soundtrack).

There’s no doubt this makes for compelling television — The Biggest Loser never fails to be a watercooler talking point — but you have to wonder what it does to the contestants’ bodies in the long-term.

A number of former TBL stars have struggled to maintain the weight they ended the show on, and according to a new research, this is not simply due to a lack of willpower, or the fact that they no longer have access to 24/7 trainers. It largely comes down to how the program impacted their metabolisms.

In a study published in the journal Obesity this week, a team of researchers examined 14 contestants from The Biggest Loser‘s eighth US season to see what had happened to their bodies six years after the show.

Watch: Mia Freedman interviews The Biggest Loser coach Michelle Bridges. (Post continues after video.)

What they found was quite stunning: in the time that had passed, the contestants’ bodies had actually fought to regain the weight they lost. Even the lead researcher was blown away by this finding.

“It is frightening and amazing,” Dr Kevin Hall, a metabolism expert, told the New York Times. 

It turns out the weight loss has affected their resting metabolism — i.e. the number of calories the body burns when at rest.

While the contestants were overweight when they started on The Biggest Loser, their resting metabolisms were perfectly normal for persons of their respective sizes. But by the end of the show, they had slowed to such a point that they weren’t burning the number of calories required to maintain their new size.

This is something the researchers expected to happen, but they were surprised to observe that the men and women’s metabolisms slowed even further as years went by, resulting in weight gain.

The Jofres won the last Australian season of The Biggest Loser. (Image: Tenplay)

"It was as if their bodies were intensifying their effort to pull the contestants back to their original weight," the New York Times writes.

As you might imagine, this came as a shock and a disappointment to the men and women in the study.

One of the most disheartened was Danny Cahill, who won that season after dropping a whopping 108kg — a Biggest Loser record at the time — in seven months.

In the six years since the show, he's gained back more than 45kg, and now has to eat 800 calories less per day than the average man of his size. Before the study findings came out, he couldn't understand why it was happening.

“All my friends were drinking beer and not gaining massive amounts of weight. The moment I started drinking beer, there goes another 20 pounds [nine kilos]. I said, ‘This is not right. Something is wrong with my body'," Cahill told the Times. (Post continues after gallery.)

Another former contestant Sean Algaier described the findings as "like hearing you have a life sentence".

He is now heavier than he was before going on The Biggest Loser, and burns 458 fewer calories than a man his size would be expected to.

Although further research into this area is required, this is certainly an interesting springboard for discussions about how the sustainability of weight loss and weight maintenance can be improved.

Featured image: Tenplay.