This Is Why It's So Hard To Keep Weight Off After Losing It

NEW YORK (CBSNewYork)-- Ever wonder why it's so hard to lose weight and then so easy to gain it back, even when you're really trying to keep it off?

Turns out your own body is sabotaging you.

Doctors at the National Institutes of Health did a follow-up on 14 contestants in a popular TV weight loss program, CBS2's Dr. Max Gomez reported. Six years after their massive weight loss, they measured the contestants' metabolic rate and found something surprising that explains why most of them had gained so much of their weight back.

"After first year of grad school I was 256 (pounds)," weight loss patient Alison Madill said.

That weight was Madill's peak, she was 5 foot 2 inches and a size 24. She managed to lost 127 pounds after gastric bypass surgery and has kept almost all of that off, but it's not easy.

"It's a daily struggle. I just say I'm metabolically broken. I'm fighting against that every day. I try to exercise at least six days a week," she said.

But millions of other people who've managed to lose weight aren't as successful as Madill. They lose and gain it right back and more.

Turns out, there's a real biological reason for that.

"Metabolical rate is reduced way out of proportion to the amount of weight that's lost... it looks like this change in metabolism is permanent," Dr. Louis Aronne, of Weill Cornell Medicine, told CBS2.

That conclusion comes from a study in the journal Obesity that measured the metabolic rate in 14 massive weight loss patients six years later.

Arrone is an obesity expert and explained that the new metabolic rate after weight loss is often hundreds of calories lower than what it should be to maintain that new lower weight. It's about how much weight you lose.

"It's extreme weight loss. So if you lose 5 to 10 percent of your body weight, you can generally hold off the weight regain. The more weight you lose, the harder it is to maintain," Aronne said.

There's a persistent change in hormones that tries to push your weight back up. Other research suggests the cause is that excess weight damages certain brain cells that regular appetite and metabolism.

"It's very, very difficult to lose weight and maintain weight loss with diet and exercise alone," Aronne said.

Because of that, Dr. Aronne said that medical experts are moving toward more aggressive drug interventions to help maintain weight loss.

The exciting news is that researchers believe they're close to figuring out how to compensate for those damaged brain cells to allow your weight thermostat to be reset.