Table 2.

Emergent themes, definitions and example quotations

Theme	Definition	Example quotations
Fixation on numbers	Developing a fixation on numbers associated with food and exercise, an acute awareness of calories, an altered relationship with food and/or a need for exactness from the quantifications within the app	‘I think it's [logging food and exercise everyday] definitely very triggering because you look at food differently. Like now when I look at food, I see like that's protein, that's fat, that's carbs instead of like that's a chicken breast, that's peanut butter, that's a piece of bread… it's definitely very, very triggering to be tracking it all the time. And especially back then [during my eating disorder], it was like, “Well, that's 100 calories right there, like I need to eat broccoli instead, that's like 35 calories”… It's a number game basically….’ [U06]
		‘I try to get exactly on [the number]… I like having it exactly on… It [the app] made me more OCD [obsessive compulsive disorder] ‘cause I'm like, “I have to hit this number”, basically… making sure I hit those numbers… There was one time my parents wanted to go out to dinner… So, I called the [restaurant] so I could already track it and have it as close as possible. And then my parents get here, and they're like, “Oh, we're going go to [this other restaurant] instead”. And I was literally having anxiety about going. I didn't want to go to dinner. I was like, “No. I already had everything perfectly planned for my day”, and that was probably a bad moment… I feel like eating disorders stem from people trying to be perfect, and with this, you're hitting numbers trying to be perfect, so I think that could be kind of bad’ [U14]
Rigid diet	Developing a strict and rigid diet, including eating the same foods every day and/or developing safe and fear foods through the use of the app's food database, personalised prior meals or the barcode scanner	‘I think another kind of bad thing about it is I eat the same thing almost every single day except for dinner, but I think like just because in my head, I can kind of keep track of the points, and I think that's probably part of it. I'm not going to eat like a lot of new stuff if I have to like kind of go and do the work for it and see how much it is, so I think that kind of makes me eat the same thing every day’ [U08]
		‘I love how it could scan a label… That was my favourite thing in the world… It got to the point where I would never buy something that didn't have a label on it ‘cause I couldn't track it… And I would be very secretive about just having a picture and being able to successfully find it on the app. If I couldn't find it on the app, I wasn't going to eat it ‘cause… It wouldn't have been correct… You start to eat the same things… ’[U17]
Obsession	Becoming obsessed with logging and tracking, which can lead to the development of obsessive thoughts around food and exercise	‘I just think the entire app in general is harmful… For someone like me, it's extremely dangerous. Just everything. Being able to log your calories, ‘cause you become obsessive over taking pictures of labels, you're measuring things, and getting the correct amounts becomes impulsive and just like obsessive. Exercise then, plays a same role in that… I got to be honest: before I started using the app, I felt like my logging wasn't that dangerous. It wasn't that compulsive or that obsessive, I should say…’ [U17]
		‘…I remember, I had that year at least five, six anxiety attacks because I was so anxious about what I'm eating, and I was so nervous about it. And the app said one thing and then the computer said something else, and I just lost my mind… So for me, it emotionally was a bad thing, the app… That's when I was really obsessing, and I would make sure everything is measured to the centimetre, to the ounce… I think it [the app] makes us overthink food, which can lead to obsessing about it… So I think the focus should be way more on health and way less of numbers… I think this [the app] just reinforces the wrong thing’ [U12]
App dependency	Feeling that one needs the app, feeling safe and in control with the app, developing anxiety when not using the app and/or not wanting to cease app use	‘In the moment, I didn't care. I knew it [the app] was harming my brain because I knew it was messing with my head mentally, but I just wanted to keep it because I felt like that was the one thing I could control. Because when you have an eating disorder, that's the one thing you want, is control. And I knew this app gave me control over what my parents wanted me to eat, just in that sense. I never really told them ‘cause I didn't want to lose that control I had. Because being forced to eat a sandwich or being forced to eat, to go see a therapist, I had no control over those, but with the app, I felt like I had control over one part of my life that I really wanted to change’ [U21]
		‘Last summer, I had to delete it [the app]. I deleted it and had to get it back ‘cause I was like, “Oh, my gosh, I need to know what I'm eating”… I literally got anxiety, so I had to get it back… I was like, “Maybe I should just stop tracking and just eat intuitively”. So, that's why I tried deleting it. And then like a few days later, I had to get it back…’ [U14]
High sense of achievement	Feeling extremely rewarded for eating under calorie and nutrient budget, engaging in compensatory behaviours and inputting them on the app, and losing weight; often occurs when receiving positive feedback on the app, such as via green visualisations	‘I definitely would say that if I got to the end of the day… like if on Tuesday, I was a little bit more in the green [on] Wednesday, I'd feel better about it. So it was almost like an accomplishment per se… Sustaining it [my eating disorder] would absolutely be seeing that when you're low or you're in the green… You don't even think about green being a good thing but just the colour cues that you associate with rewards… when you're starting to reinforce eating less, eating less, eating less… So I think it's [the app's] very much targeted towards the weight loss rather than fitness, per se’ [U19]
		‘I obviously like to be in the green for the calories remaining… This thing, progress bar, I mean, I kind of like, I mean, I used to like to see it really close to that like goal line or even like below, which sounds bad. But because that looked better to me if the bar's lower. So I mean, I guess, maybe that's kind of a problem, but I mean, it kind of made me feel that I was kind of like successful for the week if it was like mostly under the bar, obviously [laughs] even though that's under your calorie thing, which is probably not good… I just kind of wanted to see where I was in my calories for the day, and if I was like under what they allotted me, then I was happy… If I went to this bar and I saw everything was like below the goal, then that would kind of make feel like all right, that was good’ [U04]
Extreme negative emotions	Feeling extreme negative emotions, such as guilt, embarrassment and shame, especially when exceeding one's calorie or nutrient budget or gaining weight; often occurs when receiving negative feedback on the app, such as via red visualisations	‘At the end of the day, if I was still very hungry and I didn't have any calories left, that whole red number… That red number would scare me a lot because I'd be like, “Well, now I can't eat anything, and I'm really hungry, and I can't sleep with an empty stomach”. Then if I ended up eating, I would wake up feeling guilt for going over my intake because I felt like it would get in the way of my goal of losing weight… Once it hit 200 or more, I would get really stressed out, even panic because… I would be ashamed because I felt like I wasted my whole day of when I was fasting ‘cause when I was fasting, it would be a really low goal of calories… So it was just very stressful to deal with the red numbers… The red number would come, and I'd be over my calories, and it just freaks me out all the time. I wouldn't even want to go to school if I knew I ate too much that night or that day before… I feel guilt for what I ate that day ‘cause it's usually something that was high in calories, like a cookie or something. And then that caused that to become a fear food, like dietitians like to call it, a fear food that I try to exclude from my diet because that leads to a red number that embarrasses me’ [U21]
		‘I don't like the colour red. I feel like it's bad, and it would always be like a frowny face, like bad, like you didn't do what you're supposed to today, and I was like, “I know, I know I didn't”… I think they definitely need to be not as like strongly represented. Like if you're 1 calorie over, it's like, “Ok, like no big deal”. It should be like a range, you know what I'm saying? One calorie over is different than being like 400 calories over, and I think it definitely gave me the wrong perception and made me kind of go like the other way especially like when all my things were red in [my] app, I was like, “Ok, well, then this makes me definitely not want to eat for like 3 days after seeing that”’ [U05]
Motivation from ‘negative’ messages	Feeling motivated by ‘warning’ messages usually intended to curb unhealthy behaviours, such as feedback that states low weight or low calorie intake	‘…I was under-eating, so they [the app] would show me, you would be 90 pounds in a month or something if you kept on eating like this… I would just under-eat more to make that happen faster… So, I used to exercise 400 calories, then I would just skip lunch, I would eat dinner… Over here it would be 500 remaining or something. And at that point it would be, “Ok, so you're going to be 95 pounds if you kept on eating like this in 2 weeks”. So that was more of a motivation, I think… Because you're trying to lose so much weight, and you're like, “If you keep on under-eating, you're going to be 98 pounds”, which is exactly what you want to be at that point… It's not a warning…’ [U22]
		‘If you click this “Complete Diary”… So it tells you, “If every day were like today, you would weigh this amount”, which [laughs] it's like I have such mixed feelings about it because like it can be motivating, but also it can be really triggering… like someone with an eating disorder is like, “Yeah, yeah, you're right; oh my god, I can weigh less than that in 5 weeks if I eat less”… When you're in the middle of your eating disorder, you think this is motivational, but when you look back on it, it's like, that's horrible [laughs], like that's really horrible’ [U06]
Excess competition	Making calorie consumption, expenditure and weight loss a game by trying to beat the app or self; often achieved by netting fewer calories each day and/or being under budget	‘It was kind of like a game to beat the calories, kind of. So one day I had a 0, maybe it was like a negative calorie. I was like, “Oh, wow, like look at me, like that's cool!”…Just because like you can visualise what you're eating, so the more you don't eat, it's like, “Oh, I beat the app!”… I definitely wanted to beat the calories they gave me. I feel like that kind of does start an eating behaviour where you don't want to eat anything… Like especially ‘cause they give you a calorie limit. I know when I was under the calorie limit, I was like, “Ok, I won today”… I was like, wait a second, the app kind of like made it a game for me to like not eat much’ [U07]
		‘It just became this weird competition thing with it [the app]… I would just be like, “I need to be lower than what it was before”. [laughs] I don't know… It just always had to be less than the day before in the food and the weight and everything… Because then, if I wasn't, then I was like a failure ‘cause that was what the eating disorder thoughts were telling me’ [U13]