Obesity is one of the biggest public health challenges of the 21st century. At least 650 million adults are currently obese worldwide [1], and effectiveness of obesity treatments is rather modest [2]. Effective prevention methods are needed to halt the obesity epidemic.

Obesity develops with age and can only be prevented before it has developed. The transition from adolescence to young adulthood is a critical life period with rapid weight gain [3-5]. We currently have the largest ever generation of adolescents and young people and the most vulnerable to obesity and secondary noncommunicable diseases in human history [6]. Effective promotion of sustainable health behaviors to prevent obesity must specifically target people where primary prevention is still possible. At age 18 years, the prevalence of body mass index (BMI)>30 kg/m² (5.8%) and BMI>25 kg/m² (22.8%), are still relatively low, which more than double by age 35 years [7]. Body weights rise most rapidly between ages 13 to 24 years internationally [8-14], with steeper weight gain trajectories most likely to reach BMI>30 kg/m², now affecting 40% by age 65 years in the United Kingdom [15].

Adolescence and young adulthood present vital opportunities for intervention, with multiple lifestyle changes for emerging young adults—self-determining, financially independent, outside parental controls [16]. Social interactions often revolve around heavily marketed foods and drinks, tending to promote greater consumption [17]. Young people tend to be relatively neglected by conventional health promotion, considered hard to reach through lack of interface with health information dissemination or engagement with health professionals [18]. The internet has become the dominant mode for communication, information exchange, and increasingly for health care delivery. Thus, electronic health (electronic technology in health care) and mobile health (mHealth; mobile technology in health care) offer numerous advantages above traditional methods [19]. Although conventional didactic methods lack reach, innovative electronic learning and support can prevent unwanted weight gain in young adults [20]. Transferring existing online resources with proven effectiveness for weight gain prevention into mobile apps could reach a much greater proportion of the at-risk young population. Near-universal mobile phone ownership, projected to reach 5 billion by 2019, has been matched by increasing availability and access to mHealth apps, mostly for weight loss and fitness [21]. Mobile app downloads reached 149.3 billion in 2016 [22]. Over 25,000 apps are currently aimed solely at weight management [23], but few (0.17%) report having incorporated experts’ and users’ inputs during development. Even fewer have been tested for effectiveness, mostly with poor results [24,25]. Efforts to treat established obesity in young people have been rather ineffective [26,27], and there are no apps specifically tailored to offer weight gain prevention for young people.

This study used newer information technology (IT) methods to explore the views of young people from several countries on weight gain and its prevention and their opinions and preferences to inform development of weight gain prevention apps tailored to the needs of young people.

A mixed methods study design was used, with an online survey followed by online asynchronous focus groups [28]. This approach integrates quantitative and qualitative data within a single investigation, to permit a more complete and synergistic utilization of data than separate quantitative and qualitative data collection and analyses [29,30]. The study was approved by the Institutional Ethical Review Board of the Catholic University of Louvain.

The recruitment questionnaire comprised 18 questions: 2 multiple choice questions (country of residence, current occupation), 7 dichotomous questions (parents’ academic degree, parents’ smoking, participants’ smoking, concern about weight gain, interest in a quiz to estimate risk of weight gain, current use of mobile apps, interest in an app specifically designed by researchers on weight gain prevention), 8 demographic questions (gender, age range 13-24 years, postcode, current weight, current height, current waist size, dress size, email address), and 1 open-ended question (if you are using lifestyle mobile apps, which ones are you currently using; Multimedia Appendix 1).

The questionnaire was developed following an iterative process, through discussions with all coauthors based in the different countries participating in this study, to ensure that the questions were culturally appropriate. A draft questionnaire was trialed among colleagues first, and after necessary edits, the final questionnaire was trialed with a small group of young people to ensure all functions worked in the online environment and that the wording of the questions was appropriate for this age group, especially for the countries where English is not the official first language.

This was a closed survey, available only to young people aged between 13 to 24 years and residing in 1 of the 6 countries (Belgium, Singapore, New Zealand, Finland, UK, and Greece). Young people were recruited via an online advertisement service (Facebook). The advertisements appeared in a pop-up format, in the profiles of those who declared their age to be between 13 to 24 years and residing in 1 of 6 countries where English is either an official language (United Kingdom, New Zealand, and Singapore) or widely spoken and understood among young people (Greece, Belgium, and Finland). The advertisement invited young people to help guide researchers in building a mobile app, with a link to the online recruitment questionnaire. Participants were not required to have any particular interest in weight management or health, and no financial or other incentives were offered. The recruitment questionnaire was available in 2 screens in total; the first containing the subject information sheet with information on the study and the second containing the questions. The collected data were managed by SurveyMonkey, where they were automatically recorded and saved. When the advertisement and recruitment closed, data were downloaded and transferred to a university computer, which is encrypted to ensure data protection. Internet protocol addresses were recorded automatically when participants completed the online survey and checked to ensure no multiple entries were submitted by the same participant.

A subject information sheet with information on the study and the principal investigator and contact details to express any concerns they might have on the questionnaire was incorporated in the first page of the questionnaire. People following the link could read the information and decide if they wanted to proceed with the questionnaire. No data were stored for incomplete questionnaires. Respondents were assured anonymity but also invited to provide their email address if they wished to participate in an online focus group in which some of the questions could be discussed further. Those who volunteered to participate in the focus groups were first separated by age group into adolescents (13-17 years) or young adults (18-24 years) and then block-randomized into 8 groups by gender and country, so that these characteristics were uniformly distributed across groups (Figure 1). The focus groups were conducted on an online platform in password-protected Web rooms (ProBoards). The focus groups were asynchronous, open 24 hours/day for 2 weeks to accommodate participants from all different time zones and life/school/work schedules, allowing more views to be documented.

The focus group moderator (CKN) posted information on the study, ground rules on group etiquette, confidentiality, ethical considerations and consent, and a discussion guide in every Web room. A discussion guide (Multimedia Appendix 2) was created to guide the focus groups, with open-ended questions and prompts to introduce preselected topics: (1) current use of lifestyle apps, (2) factors motivating downloading and retaining apps, (3) use of social media, (4) concerns about weight gain, and (5) concerns about environmental and ethical issues around food and drink production and distribution. Topics 3 and 4 (Multimedia Appendix 2) were included based on the results of a previous study in young adults that found 2 different behavioral change theories: the rational and the stealth theories to be effective in preventing the usual weight gain in this population [20]. The rational choice theory by Simon (1955) [31] states that humans, provided they have the right information, will make a rational choice [31], whereas the stealth theory by Robinson (2010) [32] states that humans can change a behavior if they find a behavior that is motivating in itself [32].

Online focus groups have advantages and disadvantages compared with conventional face-to-face focus groups. They can involve large numbers; an anonymity may permit more open answers: the moderator emphasized that all responses were welcomed, that none would be considered right or wrong, but that they were monitored for any inappropriate content or behavior. Being unable to share facial expressions, which contribute to face-to-face focus groups, participants were encouraged to use emoticons in their postings which were used in the analysis.

Descriptive statistics used SPSS 24 (IBM). Differences between groups were tested with the MedCalc statistical software (MedCalc). Weight, height, and BMI centiles for adolescents (aged 13-18 years) were calculated according to the International Obesity Task Force [33].

Transcribed data were transferred to software (NVivo, version 11, QSR International) for analysis. Thematic analysis was chosen as the most appropriate analytical method through its ability to identify patterned meanings across a dataset and responses [34]. Coding and analysis were carried out using as described by Braun and Clark [35]. Analysis of transcripts started with multiple readings by the principal researcher (CKN) to identify keywords and phrases. Relevant words and phrases identified were coded, and data were categorized describing main issues reported by participants.

All initial codes relevant to the discussion guide and research question were grouped into themes by combining similar codes. Codes and themes were triangulated between the first and last authors to enhance the validity of the coding phrases, and all authors reviewed the selective codes, themes, and exemplar quotes. Main themes emerged from relevant combinations of named themes, each accompanied by a detailed analysis, to explain the salient sections of data collected from the focus groups.

Reflexivity relates to sensitivity to the ways in which the researcher and the research process may shape the data collected, including the role of prior assumptions and experience. This study was carried out online; hence, the researcher had minimal contact with the participants during recruitment and conducting of the focus groups. The participants could enter the Web room at any time and from any place when they felt comfortable to do so. Our study was designed to elicit contributions from a broad range of participants. During the focus group process, no individual’s views were preferred over those of others. A goal of data analysis was the identification of common themes that emerged from comparison across the focus groups. However, equal importance was attached to the analysis focusing on the details of individuals’ reports relating to specific views and experiences as well as those of the groups as a whole.

Results are reported according to the Checklist for Reporting Results of Internet E-Surveys [36].

Over an 84-hour period after posting the Facebook advertisement, 2285 young people aged 13 to 24 years (610 adolescents aged 13-17 years and 1675 young adults aged 18-24 years) responded to the advertisement and completed the survey. Demographic information for those completing the survey is presented in Tables 1 and 2.

Young people (1645/2285, 71.99%) reported being concerned about weight gain for themselves or friends, with more young adults (aged 18-24 years) being concerned than adolescents (aged 13-17 years; χ²₁=18.6, P<.001). There were no differences between countries among young adults for expressing concern about unwanted weight gain, but there was a greater range for adolescents, for example, between Finland (55.4%) and Greece (76.2%). A similar percentage of young people (1657/2285, 73.30%) reported being interested in a weight gain prevention app, again with significantly more young adults being interested in such an app than adolescents (χ²₁=11.4, P=.001). Approximately half of the young adults (49.7%, 833/1676) and one-third of the adolescents (31.0%, 189/610) reported currently using a lifestyle mobile app with significantly more young adults currently using 1 (χ²₁=–172.4, P<.001). Among young people, there was no difference in the BMI of those who reported using lifestyle apps and those who did not (21.9 kg/m²-22.0 kg/m²). Reasons mentioned by participants for not using apps were as follows: time-consuming, not reliable information/source, and too many advertisements. Similarly, for adolescents, there was no significant difference in BMI centiles of those who reported using a lifestyle app and those who did not. In adolescents, reported use of lifestyle apps increased with age, from 27.6% at age 13 years to 40.8% at age 17 years, (χ²₁=23.5, P<.001).

From the 2285-young people who completed the survey, 807 young people (376 adolescents aged 13-17 years and 431 young adults aged 18-24 years) offered and were contacted to participate in the focus groups, stratified by country and age. A total of 12 focus group sessions, held in total at the start of 2017, were completed by 719 young people (completion rate 89%). Detailed demographic characteristics of focus group participants are presented in Tables 1 and 2. Due to the large number of participants, some quantitative analysis was possible. The mean number of individual entries into each focus group for the adolescents was 98 (SD 6.0) and for the young adults 121 (SD 12.0). The moderator tried to observe rather than participate to allow participants to freely express themselves. The moderator checked the Web rooms for any inappropriate content every 12 hours and interacted individually with a total of 23 participants. Moreover, because of the nature of the asynchronous groups and participants being based in 6 countries, all but 2 (Belgium and Finland) in different time zones, participants and moderator logged in at different times and they were not online concurrently.

Main themes emerging from both adolescents’ and young adults’ focus groups are identified and presented with a general explanation of findings and exemplar quotes. Some of the main themes emerging, unsurprisingly, matched the topics which had been introduced into the focus groups.

Our results show that young people from 6 different countries are not only concerned about weight changes and diet but also about the relationships with the environment they live in. They would like independent advice to help them negotiate the environment to control weight changes, with lifestyle choices, which also help protect the environment. They are clear that guidance should be in a format that is familiar to them and easily accessible, that is, through a mobile device as long as their concerns are being addressed.

To the best of our knowledge, this is the first study to be conducted among young people at a multicounty level on the potential of mobile apps for weight gain prevention. The mixed online methods used made this possible, bringing young people from 6 countries to the same room to discuss topics of common interest. It offered some advantages including the opportunity for participants to provide candid honest, opinions from a position of anonymity. Online focus groups permit many more participants to join and avoid the effort and cost of transcribing recorded discussions, but the resulting discussions may be narrower than in conventional one-to-one focus groups where participants may be more inclined to pick up collateral or tangential issues, and there is a greater opportunity to identify cross-cutting themes. The electronic discussion among young people from different countries set up a stimulus-response reaction that revealed young people’s preferences, concerns, and barriers to using technology for managing their lifestyle. The participants, from 6 countries, reported experiencing our globalized world in a remarkably similar way, sharing common concerns and preferences. Although commonly concerned about unwanted weight gain and welcoming advice on prevention, they are concerned to have reliable information sources and for their data and identities to be protected. Younger people are reliant on mobile communications. They are well adapted to the wider digital environment and also well aware of its potential perils and how their online activity might affect their future. As experienced users, they want end products to meet closely their requirements and needs and not waste time or money.

The main topics/themes incorporated in the design of our questionnaire, and in leading the focus group discussions, were chosen because they are already established as frequent areas of concern to young people in other contexts. Other topics, such as online safety, data usage, and professional and trustworthy advice arose in the focus group discussions. It was important for this study to confirm that the main known issues apply to the subset of young people who have body weight concerns and who may be attracted to use apps directed at preventing weight gain. These individuals may have subtly different attitudes toward decision making, health risks, and risks in general, and they are known to be tempted to spend large amounts of money online for products without evidence for value. The results of the questionnaires tend to confirm that young people do indeed have similar areas of concerns around online/app approaches directed at body weight control.

There is growing interest in Web-based approaches for health under the current World Health Organization Research Agenda, with a view to develop Health in your Pocket interventions [37]. The European Commission echoes this with calls for a digital single market [38]. Obesity has become a global public health issue, affecting both developed and developing countries. Solutions that have the potential to be scaled up to reach large populations are therefore vital.

Mobile apps seem to have the potential to increase motivation to eat a more healthful diet [39], but limited research is available about the use of mobile apps for health promotion for adolescents [40] and young people. The digitalized world, which younger generations are in tune with, offers ways to implement solutions that are affordable and have global reach [41]. By the year 2020, an entire generation will have grown up in a fully digital world, with computers, internet, mobile phones, and social networking all being second nature.

Although the issues appear very similar in the 6 countries studied, there are limitations. In this study, only English language was used for the online focus groups. The countries were selected as those where large proportions of young people speak English at a high standard, but the participants may have been individuals with relatively high educational attainment, and their views are not necessarily reflective of non-English speakers in those countries. To take account of this issue, we offered the recruitment advertisement in both English and the local languages. The high consistency in results between countries where English is usually the first language across social and educational classes (United Kingdom, Singapore, New Zealand) and those where English is usually a second language (Belgium, Greece, Finland) suggests that the results may be widely generalizable. We did not include developing countries where socially determined obesity risks and diets are very different, and mobile phone ownership is lower. This study used a relatively new recruitment method for research, with advertisements posted on social media. This ensured maximum visibility across the participating countries and unified adoption with the same approach in all countries. The online method allowed for far more young people to participate than traditional focus groups. The advertisements did not mention weight or health to reduce selection bias and to attract a broad range of participants. Both recruitment and conducting methods were low-cost, convenient, and confidential, suited to reaching young people and for addressing sensitive topics such as body weight. There was no requirement for labor-intensive transcription with online focus groups.

The mixed methods design used in this study also helped with gauging this new topic in a more efficient and comprehensive way, by combing qualitative and quantitative data.

All focus group methods engage with subsectors of the target population that are interested in the topic and have time available. The online approach allows a wide section to participate, in their own time, but does introduce some limitations. The lack of face-to-face interaction and visual cues to influence discussions has been mentioned, but freedom from shyness allows participants to exchange views more freely and avoids intimidation. Furthermore, participants used emoticons to express their feelings. Young people are especially familiar with the use of emoticons, and they feel that emoticons can clarify meaning to the text [52]. Our focus groups were mixed in gender and stratified by age and country. Some researchers have preferred gender-specific focus groups for fear of males dominating the discussion—the peacock effect [53]. This effect is less likely in the online environment where participants could log in and express views at any time without threat from others. Online focus groups inevitably have some different characteristics from conventional face-to-face focus groups, being akin to moderated discussion fora, or blogs, and whether they generate the same research information needs separate investigation.

Young people are commonly, and consistently across 6 countries, concerned about weight gain and obesity. Applying no industry evidence-based IT programs to guide young people toward preventing weight gain would be well received, provided that the views of young people themselves are incorporated in the program content and app design.