Transcript for When Obsessing Over Healthy Eating Turns Dangerous
If you struggle to stay away from an afternoon candy war or French fries at dinner, you may not believe that trying to be too healthy can be a serious issue. Even dangerous. But tonight, some of those who suffer from this little known compulsion take us inside their meticulous and often maddening words. Here's my "Nightline" co-anchor juju Chang. Reporter: 8:00 A.M. Breakfast time in Santa Monica, California. Always afraid to mess this up. Jimmy: J . Reporter: Jenny is preparing her meal. If something doesn't come out the way I want it to, I will just throw it away. Reporter: But in jenny's mind, something's gone terribly wrong. I'm not doing this very well. That's a major fail. I know that if I eat it, it's not going to be appetizing to me. Reporter: She's an extreme perfectionist. Not only must it look perfect, it has to be perfectly nutritio nutritious. This is coconut oil that I like to mash into. And I don't deprive myself of calories. I want to nourish my body and eat well. Reporter: But her compulsive attention to every morsel has morphed into a full blown eating disorder. One you might have never heard of. It literally means a fixation with righteous eating. It's taken a huge toll on my body. I recently found out that I have adree Nall fatigue and an underactive thyroid and, you know, I haven't had a period in almost a year. Reporter: In a nation where one-third of adults are obese, you'd think an obsession with healthy food would be a good thing. But you'd be wrong. Every single day is full of anxiety over food. Reporter: There's been little research on the disorder and it's not listed in the official manual for psychological disorders. I'm scared of gluten, grains. Even eating a sweet potato for breakfast, I wonder how much sugar is in it. We don't know how prevalent it is. I think it's a reflection upon the obsession that's part of our society has with food. Reporter: Jenny was 17 when she says her eating disorder began taking over her thoughts. Six years later, every day is still a battle. I start to get nervous about what to eat. Reporter: She's struggling over whether or not to order a coconut milk latte. The drink is called immortal. I know it's good for me. I know it's actually really healthy. Reporter: She orders the latte. Revealing a clue as to why she's feeling so anxious. A day like today where I didn't work out at all, I almost don't feel like I deserve as many calories and ordering a drink like that, you know, kind of a big step for me. I think this drink is too pretty not to take a picture. Reporter: Jenny posts the picture to her instagram feed. Instagraming has been actually really amazing for me. It's connected me to a lot of other people who are also suffering from eating disorders. Reporter: Click the hash tag and you get pictures of photos of meals. More than 40,000 posts on instagram from around the world. Girls posting obsessively about each and every morsel they eat. It can signal a much larger problem. Jordan younger became a ç vegan sensation obsessively chronicling her meals on her blog. That is, until her restrictive diet devolved into the eating disorder. How does eating healthy become an eating disorder? When it turns into an obsession rather than something you're doing because you're passionate about it and because you're excited about it. It just takes over your mind. All of a sudden now, you put a picture on instagram and you have potentially hundreds or thousands of people weighing in and it's like throwing gasoline on the fire. Reporter: Jordan says she restricted her diet so much, she developed a strange rash and grew weak. And like jenny, stopped having her period. You were malnourished. I was malnourished, yeah. I was very much restricting myself through the shield of veganism. Reporter: That's when Jordan revealed her struggle with orthorexia. A dark secret she blamed on her strict vegan diet. She got a surprisingly mixed reaction. You were literally getting death threats. Yeah, I was, from people, predominant people in the vegan community. It's been a horrible backlash. People telling me that I'm an animal killer that I'm cashing in on veganism for attention. Reporter: But other fans, like jenny, remain staunch supporters, even as Jordan morphed from strict veganism to a less restrictive diet. On this day, we arrange for the two to meet. She's been a huge inspiration to me. I already kind of feel like she's a friend, so, it's going to be really great to actually meet her. Hi. Hi. So nice to meet you. I feel like I already know you. Reporter: They are kindred spirits when it comes to food. I will flip-flop back and forth because I'm so attached to having a label. Right. And it's like, if it's not vegan, then it's like the opposite, it's Paleo. And it's like, why can't I just be okay with food being food? Reporter: They both know there's a long road ahead. Once you start talking about it, you can't deny it to yourself any longer. Reporter: The ladies take comfort in knowing they're not alone. But the struggle is ultimately a solitary one. It turns you into a nasty person sometimes. I've been really rude to, you know, family and friends, just because I myself have not been in a good place. Reporter: Back home, jenny's mind turns to dinner. Just regular chicken and then do one with chicken sausage. Reporter: Tonight, her mom is joining her for a healthy spaghetti squash dinner. They often order in because the kitchen has become a battleground. Cooking with her or around her is -- is simply an anxious type of experience. It's -- I'm not very nice in the kitchen. No. She's not. It's like, she becomes possessed with food and the anxiety around it and it makes her just a very selfish person. And it's not something she means to do, it's something that just takes over her. I can't hear you elaborate anymore on it. It's getting to me. Reporter: Once her mom leaves the table, jenny reveals a startling fact about how deeply engrained the disorder is in her life. You kind of don't want to recover from it because you've put so much of yourself into being this way and I think I'm almost scared to see who I am without all of the stresses I've placed upon myself. Reporter: She's slowly trying to stop demonizing food. And tells us since filming, she's made major progress and says she's no longer obsessing over what she seats. Recovery is not easy and it's, you know, extremely easy to get down on yourself. But I know that I can do this. And I think just knowing that I can if I try hard enough is enough to push me to succeed. Reporter: For "Nightline," I'm juju Chang in New York.
This transcript has been automatically generated and may not be 100% accurate.