Losing weight is hard. More than half of Americans want to do so, but keeping it off is even harder. Research shows that 80 to 95 percent of people who lose weight regain it within three to five years, according to data from the National Institutes of Health and the Obesity Society.
Scientists say that’s not a failure of willpower. Hormones, genetics, and even evolution push the body to fight back—driving hunger up, slowing metabolism, and urging the pounds to return. It’s a biological tug-of-war that popular culture rarely acknowledges, says Kimberly Gudzune, medical director for the American Board of Obesity Medicine.
“There’s this presumption that we have that once you’re there, it just magically stays there. But unfortunately, that is really not the case,” she says.
For decades, dieting has been framed as a battle of discipline. Researchers are now beginning to understand why the body resists weight loss so fiercely—and how hormones, brain chemistry, and even early life experiences set the stage for lifelong weight regulation.
What reality TV taught scientists about weight loss
Pop culture has long glorified dramatic weight loss, rarely showing what comes after. Few examples made that clearer than The Biggest Loser, a reality series that aired from 2002 to 2016. Contestants were rewarded for shedding as much bodyweight as possible, supported by teams of trainers, nutritionists, and medical staff—but for scientists, it also revealed how the body resists transformation.