Table 4 Summary of feasibility study themes from participant interviews (phase 2) that led to iterative changes or highlighted considerations for a definitive RCT

Wider benefits

• ‘It is not just me. It is my husband as well. I make what he eats. He has noticed a change. He has lost weight as well you know’ P005

• ‘When I’ve been listening to you, I’ve been saying to my wife and she has been doing a few of the habits as well’ P001

• A consideration to inquire about the impact of the intervention of others in the household when writing researcher notes

RCT considerations

• ‘There would be no problem coming to my house [for study visits]’ P002

• ‘Well I am a private person and I think this is [study visits] ideal in this situation and environment [Centre for Dentistry]’ P005

• Conducting study appointments at participant’s homes to be incorporated into an RCT in order to maximise engagement by overcoming accessibility barriers to Centre for Dentistry

• ‘I think if you had a longer list of the variety of food [of healthy habit examples to choose from]’ P009

• Greater flexibility to list of healthy habits was added

• ‘Some of the questionnaires were a bit repetitive. I still don’t know what the difference was between I plan to do something and I intend to do something so I answered the same for those as I really didn’t know what the difference was’ P007

• Highlighted the need for more in depth explanation from the researcher to explain concepts of the questionnaires

Intervention barriers

• ‘My biggest problem is I’m getting no exercise and it’s not helping my weight problem. I can only do a limited walk with [wife] you know’ P002

• International Physical Activity Questionnaire (IPAQ) added to provide further insight into weight status [32]

Process of habit-formation

• ‘The wholegrains one is still work in progress’ P003

• A longer follow up time was added to investigate how long it takes to form a healthy habit

Use of prompts to aid habit formation

• ‘I don’t need such a formal approach [referring to tracking sheets]… probably these meetings have been useful to prompt me to do that instead’ P003

• ‘I did yes [found tracking sheet useful] because I require prompts… my memory its bad and occasionally I need a wee prompt to remember to do things…That’s the nature of me at my age’ P001

• As tracking sheets provoked a mixed response habits were only to be tracked for the first 6 weeks (intervention delivery phase)

• ‘I liked the illustration of the vegetables, proteins and the whole-wheat. I thought right what am I going to do today and had a look at it’ P009

• Further photos added to intervention booklet for healthy habit ideas