Keep in mind that on "Biggest Loser," all the contestants are closely medically supervised while on extreme diets and extreme exercise plans. Also keep in mind that these people are morbidly obese (BMI > 40), and that this is just a TV show. The term "reality show" does not necessarily imply that it has basis in reality.
Regarding a diagnosis of anorexia, a person's BMI is irrelevant. A person with anorexia has a distorted view of his or her own body, which causes them a lot of anxiety, which is the driver of extreme dieting and extreme exercising.
The reason the contestants on "Biggest Loser" are not considered pathological anorexics is because it is not a distorted body image that is driving them to adopt an extreme weight-loss plan; they adopt the (medically supervised) extreme weight-loss plan because they have an extreme amount of weight to lose.
A person of normal weight should not adopt such extreme measures because they do not have to lose an extreme amount of weight. Slimming down a little is fine, but when a person only wants to lose 15 or 20 pounds, a gigantic daily calorie deficit isn't necessary, and can be harmful.
Two hours of cardio a day (staying under maximum heart rate) is excellent. Eating around 1800 calories or fewer a day for men or around fewer than 1200 calories a day for women, though, can be harmful to the body. There is a minimum daily calorie threshold the body requires for all systems (immune system, nervous system, the brain, etc.) to be operating at 100%.
On top of that, if a person gets too few calories, the body goes into starvation mode, and essentially hangs on to every bit of energy it can by slowing the metabolism to a crawl, which can make losing weight more difficult.
At my peak, my BMI was 41, so I unfortunately understand the anxiety and depression that come with the constant bombardment of messages from our society telling us all that we should not be fat, and the desire for all the weight to be gone NOW instead of losing it gradually. I was suicidal over my weight, and had started abusing laxatives (but wasn't losing any weight).
I got professional help through my doctor (as well as weight-loss expectations that were realistic, for once), and now I've lost 80 pounds with 40 more to go, and don't get depressed anymore.
I consume between 1900 and 2100 calories a day (because I'm male and tall), I get 90 minutes of cardio 5-6 days a week (running, biking, and swimming), and I lift weights 2-3 times a week.
After I hit my target weight, I plan to increase the amount of calories I consume to just under what I burn to maintain my weight, but keep exercising just as much.
Remember to take care of your body, because you only get one. I hope you meet your goal. Keep us posted.