While dramatic weight loss is great for ratings, it may be a killer for metabolisms. A study out this week in the journal Obesity followed 14 participants from “The Biggest Loser” and found that all but one gained back much of the weight they’d lost — and no wonder. They experienced massive metabolic shifts: To maintain their weight, they had to eat up to 500 fewer calories than similarly sized peers who hadn’t been on a reality-TV crash diet.

“When you reduce the calories you consume, your metabolic rate reduces proportionally,” explains Jason Fung, MD, author of “The Obesity Code,” who’s not connected to the study.

“Imagine if you made $100,000 a year. Then, all of a sudden, your salary was cut to $50,000. Would you still have the budget to ‘spend’ $100,000 a year? No. You’d have to tighten your budget, just like your body automatically tightens its calorie expenditure when your body weighs less than it did before.”

Another weighty issue? “The Biggest Loser” contestants experienced a massive drop in leptin, a hormone that controls hunger. That’s a danger faced by all dieters, though to what degree remains unclear, especially since leptin levels can be impacted by sleep and stress. (A “Biggest Loser” spokesman says the show’s lead doctor is evaluating the study’s findings.)

Bottom line?

While dieters looking to drop pounds will likely experience similar metabolic changes — and long-term challenges — they aren’t as likely to be as extreme.

Still, everyone could benefit from a weight loss plan that’s gradual and considered — in other words, the opposite of “The Biggest Loser.”

Here’s what the show gets wrong about weight loss, and how you can shed pounds — and keep them off.

MYTH: Extreme exercise is good

Contestants soaked in sweat, heaving tires around a ranch for hours and hours, might make for good TV, but it’s not smart.

“The type of diet and exercise performed on the show works short term, but it simply isn’t sustainable for ‘real’ life,” notes William Dietz, MD, obesity expert and director of the Sumner M. Redstone Global Center for Prevention and Wellness at George Washington University. When contestants go back to real life and can’t exercise for hours and hours, the weight can easily creep back on.

THE FIX: A 2013 study from Ontario’s University of Guelph suggests that high-intensity interval training (HIIT) workouts — short intervals of hard work with rest in between — may be the key to permanently boosting resting metabolism. So if you’re hitting the gym, think quality, not quantity.

MYTH: Drop weight as fast as possible

“Extreme weight loss also results in the loss of lean muscle. When you lose lean muscle, your metabolism slows,” explains Rekha Kumar, MD, an endocrinologist at Weill Cornell Medicine.

THE FIX: Focusing your weight loss goals to 1 to 2 pounds per week helps preserve lean muscle mass. Kumar also suggests incorporating yoga, weight lifting or pilates into your workout routine at least two or three times a week.

MYTH: A low-fat diet will lead to weight loss

“The Biggest Loser” contestants are often counseled to eat low-fat and fat-free dairy and processed foods from the show’s sponsors, such as Vita frozen seafood dishes.

THE FIX: Nutritionists and diet doctors say fatty foods like avocados, nuts, oily fish and peanut butter can help boost the metabolism, preserve lean muscle mass and regulate blood sugar to keep you feeling full.

MYTH: Calorie-cutting is the answer

Though the show preaches that weight loss is a prize to be won by those who have the willpower to cut calories, more and more studies are finding that it’s not that simple.

THE FIX: According to a 2013 University of Manchester study, following a fasting-type plan — a 75 percent reduction in calories for two consecutive days each week — may be far more effective for weight loss than just calorie restriction. Fung says that’s because fasting allows your body to break down fat stores for energy.

“Your body converts food to glucose, which it will then use for fuel,” explains Fung. “But when you deprive your body of food, it burns through glycogen in the liver and then moves to fat stores, resulting in actual weight loss. If you’re only reducing calories, it’s much harder for your body to reach its fat stores.”