Table 2.

Table of themes and supporting quotes.

Theme			Supporting quotes
Theme 1: barriers and facilitators to app usage
	Subtheme 1: believing that the app was effective	PPa 103: “I didn’t really see any effect of doing it so it just seemed like it wasn’t worth the effort.”
	Subtheme 2: motivation to get the daily badge	PP 34: “It made me more aware to use the app rather than just like, ‘oh, I’ll just put that in later,’ it was like ‘no, I need to get my badge today.’” PP 64: “If you’ve messed up once in a day you tend to then think ‘well, I can’t get all the stars now today’ so you know you're not going to get the trophy. So you sort of don't feel quite as competitive about getting them, but if you get them from the beginning of the day, you think ‘right, I want to get them all today.’”
	Subtheme 3: habitual, routine app use and distractions	PP 53: “I’d got into a routine that when I was in the kitchen or when I was doing meals the phone came, the picture came, everything came, but if I went out of the routine I was in, then I wouldn’t think to do it.”
	Subtheme 4: not using full app in social situations	PP 53: “If I'm out socially with friends, family, or whatever and then to just kind of interrupt and say, ‘I have to listen to this for five minutes,’ it didn’t feel right to do it.” PP 35: “I think that’s a real age thing, I am not someone who posts my food on Instagram. Also feeling a bit embarrassed that I didn’t want to have to explain to people if they said, ‘why are you taking a picture of your dinner?’”
	Subtheme 5: wanting a good-looking food gallery	PP 90: “I wanted it to look like a good gallery and not a bad one just for my own personal, I don't know, pride, satisfaction” and “it would make me want to eat more of those nice fresh homemade things.” PP 96: “I kind of stopped using it 'cause I was like ‘don't judge me.’”
	Subtheme 6: meal descriptions used for retrospective entries	PP 64: “I ended up writing the description in more than the picture towards the end.” PP 03: “Where I’d forgotten to take a photo I was trying to write in the description. But I don’t think that that worked as well as it would have done if I had of taken a photo in terms of looking back over it.”
	Subtheme 7: repetition of the audio clip	PP 103: “It was quite repetitive so I didn’t want to listen to the same thing over and over.”
Theme 2: effects of the app
	Subtheme 1: making healthier food choices	PP 92: “I had leeks last night on my carvery, which I never would have picked.”
	Subtheme 2: eating smaller portions	PP 7: “I had rice and a sweetcorn dish last night, and normally I’d put two big spoons on, and last night it was just the one and the one spoon was plenty.” PP 71: “I bought a smaller plate; I said, ‘right that’s mine,’ so I am more aware of the portion size.”
	Subtheme 3: reviewing the gallery informed eating	PP 78: “If I was hungry, I would look back to see what I've eaten, ‘ah yeah, you’ve ate plenty,’ and that would stop me.” PP 34: “I’ve noticed I’m very very bad at eating late at night.”
	Subtheme 4: greater attention to hunger and fullness	PP 63: “I’ll stop because I’m full, and I’m not eating the full thing because I’m actually full halfway through it.”
	Subtheme 5: eating more slowly	PP 4: “It’s helped me to slow down when I’m eating.”
	Subtheme 6: eating attentively when not listening to the audio clip	PP 56: “Even though I’m not listening to it, I know what it asks me to do every time. So, yes, it would get ingrained in you and you would do it.” PP 98: “Even when I’m not out with the app, I definitely chew slower.”
	Subtheme 7: enhanced eating experience	PP 22: “I noticed that I was tasting the food more and experiencing the food more.”

^aPP: participant; participant numbers exceed 39, as 104 participants (across arms) took part in the trial.