When Rachel Frederickson , 24 , stepped out onto the stage at NBC 's `` The Biggest Loser '' finale Tuesday night , some wondered if she had gone too far . While the show is known for its dramatic weight loss transformations -- most winners lose more than 50 % of their body weight -- Frederickson appeared extremely thin . And the looks on trainers Bob Harper and Jillian Michaels ' faces could be interpreted as shock -- or dismay . Frederickson went from 260 pounds to 105 pounds , losing 59.62 % of her body weight . At 5 feet , 5 inches tall , that puts her body mass index at 17.5 . Anything under 18.5 is considered by the National Institutes of Health to be underweight . NBC on Wednesday declined to comment on its $ 250,000 grand prize winner , a voice-over artist who lives in Los Angeles . Social media , however , was buzzing . `` Are you kidding ? '' One woman wrote on the show 's Facebook page . `` Rachel looks anorexic ! She has gone from one extreme to the other ! '' Other posts called Frederickson `` frail '' and said she seemed `` dizzy '' and `` disoriented '' on stage . `` She obviously worked incredibly hard to achieve her weight loss goals , but I am wondering if the pressure of winning a large cash prize caused her to take it too far , '' one said . Others posted on Frederickson 's Facebook page , asking her to get help and expressing disappointment . `` I 'm saddened that my 13-year-old daughter watched as you were rewarded for doing that to your body , '' one woman said . Frederickson as of Wednesday had not responded to the posts and had not commented on the controversy on Twitter . Michaels issued a statement late Wednesday on social media on behalf of herself and Harper , saying , `` Bob and I want to take a moment to congratulate all of the BL contestants on their hard work . We 're not comfortable commenting on Rachel 's journey because ( we ) were n't her trainers and were n't given an opportunity to work with her at any point . Any questions about the contestants on the Biggest Loser should be directed to the show 's producers . '' Asked by another Twitter user whether she was concerned about Frederickson 's weight , Michaels posted , `` We wo n't comment because we had nothing to do with it and want no part in shaming someone with 'public statements . ' '' HLNtv.com : Opinion : Dropping pounds nothing like 'Biggest Loser ' BMI applies less on an individual level and is more utilized for population norms -- many people , such as marathon runners or endurance athletes have low BMIs and are perfectly healthy . And some people who eat well and exercise normally are just naturally thin . However , losing a significant amount of weight using unhealthy methods can be dangerous , said experts unfamiliar with Frederickson . It 's the darker side of weight loss -- as obesity is unhealthy , so is being underweight . `` Can you be too thin ? Yes . Can it be as dangerous as being too fat ? Yes , '' said Dr. Steven Lamm , weight management expert and medical director of NYU 's Preston Robert Tisch Center for Men 's Health . Severe weight reduction can result in hormone disruption or bone thinning ( reduction in bone density ) and can affect women 's fertility , as they stop menstruating , said Lamm and Dr. Robert Kushner , clinical director of the Northwestern Comprehensive Center on Obesity in Chicago . Kushner said most of his patients lose about 30 % of their body weight over the course of a year . `` On the other end , I have patients with a BMI of 30 that are in perfectly good health , '' he said . Lamm notes the television show is about extremes , `` not what we as a profession are looking at . '' But `` if I were to see this in a patient , I would be concerned about their emotional stability , '' he said . Frederickson is `` just below that lower end '' on the BMI scale , Kushner said . `` Not watching the show ... I really could n't say whether she 's unhealthy , or she should n't weigh that much . Because she very well could have a healthy lifestyle . '' Still , `` there are some people who we see for weight management who develop disordered eating , '' he said . `` It 's like a pendulum and they swing to the other end ... I do n't see a lot of those patients , but I do see them . '' Such patients are afraid to gain any weight because of their fear of again becoming obese , he said . The real message , said Lamm , `` is that people should appreciate that when they are overweight they do n't have to lose 100 pounds to improve their overall health , that small changes in body weight can have a very sigificant impact on blood sugar , cholesterol . `` They should n't think that if they ca n't lose 100 pounds they should n't try . '' 'Biggest Loser ' trainer : Dumbbells and diets do n't get you in shape .
Social media is buzzing over `` The Biggest Loser '' winner 's 155-pound drop . Losing a lot of weight with unhealthy methods can be dangerous , experts say . Being too thin can be as dangerous as being obese .