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ST. LOUIS - We're used to seeing incredible transformations on the last night of the Biggest Loser.

But if you watched Tuesday night's finale here on Newschannel 5, you saw what has become one of the most debated topics of the day. Did Season 15 winner Rachel Fredrickson lose too much weight?

Fredrickson started the show at 260 pounds and dropped to 105. At 5'4", that puts her underweight for her height on a standard body mass index chart. It's been the subject of a lot of buzz in social media.

We asked Dr. Sam Klein, director of the Center for Human Nutrition at Washington University and an international expert on weight management to join us on First @ 4. He's also running weight loss studies and looking for participants in St. Louis.

If you would like to participate in a study you must be between the ages of 18 and 65 and at least 30 pounds overweight, a non-smoker and not diabetic. Call 314-747-3758 for more information.