MINNEAPOLIS (WCCO) — When Stillwater native Rachel Frederickson took home $250,000 on Tuesday night’s The Biggest Loser, Twitter lit up with criticism of the former high school swimmer. She’d shed 150 pounds over seven months to get down to a 105-pound frame. That was almost 60 percent of her body weight – the biggest percentage body weight loss in the show’s history.

“I thought she was shockingly skinny. You could see her bones,” wrote Nicole Michalik, a former contestant on the show.

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“Not a healthy look – kinda scary actually,” said Twitter user Nance Lee.

So that had us wondering: What is a healthy weight loss? We took the question to Sue Masemer, an exercise physiologist and Barb Brower, a registered dietician. Both are with Allina Health.

“Do it in moderation. You don’t want to lose a ton of weight too fast,” Brower said. “It’s not healthy. Physiologically, it can screw up your electrolyte balance, your vitamins and minerals and ultimately can affect your metabolism so that it becomes harder to have a healthy body afterward.”

Brower said Frederickson’s 150 pound weight loss over seven months is similar to a loss due to gastric bypass surgery.

“Some people can safely lose three to four pounds a week. It depends on how much weight you have and how much you’re doing it,” she said.

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Masemer says she recommends losing between one to two percent of a person’s body weight each week. If a person loses too much, their overall energy falls, they can suffer hair loss or moodiness and they are more likely to become sick.

“In losing weight quickly and losing too much, it has an overall impact on the health of the body,” Masemer said. “It puts a lot of stress on the organs, it starts to cannibalize the muscle and it can lead to some cardiac issues.”

How much is too much differs on the person – their starting weight, their body frame, their height and more. Both experts say there are two measurements – body mass index and body fat percentage – a person can use as a guideline.

Body mass index can be determined by multiplying your weight by 703, the dividing by height and dividing by height once again. Frederickson’s BMI is estimated to be around 18. Brower says between 19 and 25 is considered healthy.

Body fat percentage can be measured using skin fold measurements or a machine called a Bod Pod. Masemer says the healthy range for women’s body fat percentage is between 20 percent and 30 percent. For men, it’s between 12 to 20 percent.

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“For women to drop below that 13 percent bodyfat range has negative health consequences,” Masemer said.