In the return of its long-running series “True Life,” MTV explores the daily lives of three young adults who suffer from orthorexia nervosa, an increasingly common â€" though medically unrecognized â€" eating disorder.

“Viewers [will] meet three young people who are so obsessed with righteous eating that it's damaging their mental and physical wellbeing,” MTV said in a statement.  “…Eating healthy is actually making them sick.”

Orthorexia is defined by the National Eating Disorders Association (NEDA) as a “fixation on righteous eating.”  The disorder can stem from various causes: One woman featured in the episode, Spring Jackson, wanted to start eating healthier when she began breastfeeding her daughter; Andrew, developed a crippling fear that packaged goods would give him cancer.

For all three young adults â€" Jackson, 26; Andrew, 20, and Lauren, 20 â€" their attempts to eat healthier began innocuously enough.  However, over time, their eating habits spiraled out of control and led them to cut entire food groups from their diets.

Jackson, once a self-professed junk food lover, only ate raw fruits and vegetables.  She would force herself to purge if she ate anything cooked.  Lauren, meanwhile, had a list of only 15 “safe” foods â€" examples include oatmeal, almonds and vegetables â€" she could eat out of fear of gaining weight.  Her cheat food?  Adding cheese to a meal of egg whites.  And finally, Andrew was convinced that even a small morsel of unhealthy food would put him at risk of cancer or diabetes.

“My fixation to eat healthy and desire to be healthy slowly became more fixated on certain foods I felt were pure and correct for my body to eat,” Jackson told FoxNews.com.  “I still don't know for certain if I got sick after eating unhealthy foods was because my body had become adjusted to a raw diet or because mentally I got so distressed over it, knowing my body wasn't going to process it.  I thought it was poison essentially, because it wasn't organic or it wasn't  raw.”

Jackson said she essentially thought she might as well have cancer “because I'm just putting poison in my body.  It's in there, and it's bad.”

Though orthorexia seems as if it should improve a person's health by leading them to eat fruits and vegetables while avoiding packaged foods, the disorder can actually lead to various health problems such as malnutrition, early-onset osteoporosis, and if severe enough, can even cause fertility problems.  

In addition, the intense obsession with food “can crowd out other activities and interests, impair relationships, and become physically dangerous,” according to NEDA.  Jackson, for example, described her fixation with food as “OCD-like” and would avoid friends' parties, or even eating with her parents, due to her restricted diet.

“Changing my diet is not an option,” Jackson says in the upcoming episode, adding that she felt like she had to keep her habits a secret from her family and friends.

Part of the problem, according to NEDA, is that orthorexics lose the ability to eat intuitively â€" in other words, to recognize when they are hungry, when they are full and when they have eaten enough.

“The orthorexic never learns how to eat naturally and is destined to keep ‘falling off the wagon' and thus feeling shameful, similar to any other diet mentality,” NEDA says on its website.  However, for most othorexics, the disorder is not fueled by the desire to diet or lose weight, according to Jackson.

“It has nothing to do with weight whatsoever,” Jackson said.  “I got thin before I started purging because I was so strict with the foods I ate. I was about 98 pounds at 5'5”, which is really small for my frame. I was actually trying to gain weight because I stopped having my period.  Purging was a last resort [when I ate unhealthily] to fix and undo what I did, which I felt was wrong, or poison or not healthy.”

How orthorexia is different from anorexia

Jackson said it can be difficult for people to understand orthorexia because "as soon they hear ‘rexia' they think you're just anorexic, or you're just binge eating and throwing it up."

She said her reasons for being orthorexic are a completely different mental process.

"I don't feel I identify with people who are afraid of getting fat.  I feel like I'm in a separate class," she said.

Not all extremely healthy eaters are orthorexic, but some problem signs to look out for are: when healthy eating takes up an inordinate amount of time and attention, when eating less healthy leads to guilt or shame, or when healthy eating is used to avoid other life issues.  

To treat orthorexia, sufferers must first admit there is a problem and identify its root cause.  Then, they can begin to address their emotional issues and be less rigid in their eating habits.  In some cases, professional help is recommended or required â€" though because the disorder isn't officially recognized, not all doctors or therapists are aware of it.

Jackson said she had to explain to her therapist what orthorexia was, and even now after treatment, her relationship with food is “better but not where it needs to be.”  

“I'm looking forward to the show coming out because I want to reach out to [other people with orthorexia] and hear their experiences,” Jackson said.  “I'm hoping a lot of people will connect with me. I think it could be instrumental to my healing.”

MTV's “True Life” airs at 1 pm ET on Sunday.