NBC's reality show The Biggest Loser turns dieting into a grueling training regime fit for gladiators. The victor this past season was Roberto Hernandez. He dropped a whopping 160 pounds to reach a body weight of 188 pounds.

But once the lights, cameras, nutritionists and trainers go away, the contestants must find a way to keep the pounds off.New research into the lives of past contestants found many regain much of the weight they lost in the show — sometimes 100 pounds or more — because their biology works against them. The research appears in Monday's issue of the journal Obesity.

For more on the significance of the findings, All Things Considered host Audie Cornish spoke with Dr. Donna Ryan, an obesity researcher and clinician at the Pennington Biomedical Research Center in Baton Rouge, La.

A transcript of their conversation follows, edited for clarity.

CORNISH: We should mention that you weren't involved in doing this research, which was on the front-page of The New York Times today. [Here's the Times' story.] But I can imagine in your community, it's huge.

RYAN: Absolutely. I think the most important aspect of this research is it really reinforces how biologically determined body weight is. That it's not just a matter of willpower to produce weight loss and to keep weight off.

Let's give people some background. The study tracked contestants from 2009 — that's Season 8 of The Biggest Loser. And the researchers found that most of the 16 contestants had put back on the pounds they'd lost. This has to do with their metabolism, right?

Correct. We know that reduction in metabolic rate is a normal biologic response to weight loss. This is a disproportionate reduction of metabolic rate, and in a way it's a metabolic handicap. So that after weight loss, two people who weigh exactly the same — the one who is reduced will require less calories, less energy, to sustain that weight than a person who has never been reduced. So those Biggest Loser participants who were reduced, actually, to sustain their weight, had to eat 500 fewer calories a day than individuals of the very same weight who were never reduced.

So let's say you've lost a lot of weight, let's say you lost 100 pounds and now you're 150 pounds. Another person who is 150 pounds — they can still eat the calories they want, right? But you've got to eat less to maintain that level.

That is correct. You must eat less than a person who weighs exactly the same as you.

But you'll be hungrier, right? Because the research is also talking about another way your body fights against it.

Absolutely. All of the hormones that your body produces that regulate appetite are also altered disproportionately. So you're hungrier than that person. You're more susceptible to highly rewarding foods, to snacking.

People are going to hear this and think that, essentially, the contestants on the Biggest Loser might be worse off than they were before they lost all this weight.

Absolutely not. I think the most important thing to know about The Biggest Loser is that, in weight loss, it's not about how much weight you lose – it's about your health status. And we know that you don't need to lose dramatic amounts of weight to really get a lot of health benefit. So those people on The Biggest Loser, after six years, they were still reduced on average by about 10 percent. And that's associated with a lot of health benefits.

At the same time, I think it might be disappointing for these contestants and for other people who have had extreme weight loss. What advice do you have for them?

Copyright 2016 NPR. To see more, visit http://www.npr.org/.