Introduction

Weight-related self-monitoring (WRSM) involves tracking one’s weight or behaviors that may affect weight, such as physical activity or dietary intake. Technologies and smartphone applications (apps) designed to help individuals engage in WRSM have gained popularity in recent years and amassed millions of users. Wearable and all-in-one fitness trackers such as Fitbit have over 27 million active users a month and popular dietary-focused self-monitoring apps have nearly 20 million active users a month in the USA alone [1,2,3,4]. The popularity of WRSM apps is likely due to increased accessibility and ease of tracking that WRSM apps offer, high levels of weight and health concerns among the general population, and recommendations or incentives for WRSM by health-care professionals [5,6,7]. Prior research has suggested that emerging adults (ages: 18–29 years) are the most frequent users of such WRSM apps, but little is known about what types of apps emerging adults use or what demographic subgroups are most likely to use WRSM apps, particularly outside of college samples [8, 9].

Understanding who uses WRSM apps among the general population of emerging adults is important, given that the use of WRSM apps has been linked to both positive and negative health outcomes in this age range [10, 11]. WRSM is a key component in behavioral weight loss interventions and has been shown to lead to weight maintenance over time in structured weight management programs [12]. Notably, evidence suggests that use of technology-based WRSM yields greater weight loss and dietary quality compared to traditional forms of WRSM such as using paper food logs [13, 14]. However, it is unknown whether using WRSM apps outside of clinical programs, where there are beneficial components including social support and assistance from clinicians, yields the same effects on health behaviors [15]. Cross-sectional studies among non-clinical samples of college students have shown that dietary self-monitoring is associated with intake of a more nutrient-dense diet and that physical activity self-monitoring is associated with higher motivation for physical activity [10, 16, 17]. However, WRSM has also been linked to negative health outcomes when used outside of structured weight management programs. For example, among non-clinical samples of college students, WRSM app use has been cross-sectionally associated with elevated eating disorder risk, including higher rates of disordered eating and problematic alcohol use [11, 18, 19]. Given observed associations between WRSM app use and eating disorder risk among non-clinical samples, high incidence and prevalence of eating disorders and disordered eating in this age range [20,21,22,23], and the severe consequences of eating disorders [24], it is crucial to identify populations that may be more likely to use WRSM apps during emerging adulthood to identify vulnerable populations at risk of developing eating disorders.

Because of the cross-sectional nature of existing literature between WRSM and eating disorder risk, it is unclear which comes first; it is possible that WRSM contributes to eating disorder risk or that those who have elevated eating disorder risk use WRSM because of their elevated eating and weight-related concerns, or potentially both. If eating and weight-related concerns precede the use of WRSM apps, it may explain the cross-sectional findings between WRSM app use and eating disorder risk, as well as other eating and weight-related outcomes. If WRSM app use precedes eating and weight-related concerns, then WRSM may be a by-product or maintenance factor for eating disorder risk. Specifically, those who are interested in improving their health may opt using WRSM apps to improve nutritional intake or physical activity, while those already using unhealthy weight control behaviors (e.g., fasting) may begin using WRSM apps in an effort to gain further control, which can maintain or exacerbate their eating disorder risk. However, if elevated eating and weight-related concerns do not precede WRSM app use, it may provide further support to the theory that WRSM contributes to elevated eating disorder risk. Therefore, understanding whether eating and weight-related concerns precede the use of WRSM apps is an important first step in understanding who uses WRSM apps and why, as well as understanding the temporality of relationships between eating and weight concerns and WRSM app use. Further, because eating and weight-related concerns are more common among individuals with higher BMIs, and WRSM is often recommended clinically for weight loss among those with higher BMIs, we wanted to explore the extent to which BMI may explain associations between eating and weight-related concerns and later WRSM app use [25,26,27].

Given the widespread use of WRSM apps and known associations between WRSM app use and health outcomes such as dietary intake and eating disorder risk in emerging adulthood [10, 11, 18], it is important to understand who uses WRSM apps and what predicts WRSM app use. Therefore, the present study aims to understand (1) what types of WRSM apps emerging adults used to manage their eating, physical activity, and weight, (2) who uses WRSM apps, and (3) whether eating and weight-related concerns in adolescence predicted the use of WRSM apps in emerging adulthood. We hypothesized that measures of eating and weight-related concerns in adolescence would predict use of WRSM apps in emerging adulthood; we also aimed to explore the role of BMI in observed associations. Study findings will help inform future research examining the potential consequences and implications of WRSM app use among non-clinical samples, as well as inform public health recommendations regarding engagement with WRSM apps among the general population.

Methods

Study design and sample

Longitudinal data were collected as part of the EAT 2010–2018 (Eating and Activity over Time) study, a population-based investigation of eating and weight-related health behaviors and associated factors in a diverse sample of young people. Participants enrolled in the EAT 2010 study were adolescents (mean age = 14.4 ± 2.0 years) during the 2009–2010 academic year and completed 8-year follow-up EAT 2018 surveys as emerging adults (mean age = 22.0 ± 2.0 years). For EAT 2010 data collection, middle and senior high school students at 20 urban public schools in Minneapolis-St. Paul, Minnesota completed classroom surveys and anthropometric measures in a private area of their school. Invitations to participate in the online EAT 2018 survey were mailed to baseline participants. To further encourage participation, non-responders were mailed up to eight reminders and additional contact attempts were made using email, phone calls, text messages, messaging through social media, and home visits. The response rate at follow-up was 65.8% among participants with available contact information (n = 1568). The sample for the present study included those with data at both 2010 and 2018 who were identified as the same gender at both time points, were not high school students at 2018, and were not missing data for covariates (n = 1428). All study protocols were approved by the University of Minnesota Institutional Review Board Human Subjects Committee.

To account for missing data, inverse probability weighting was used for all analyses [28, 29]. Inverse probability weighting is the recommended method for handling missing data in longitudinal studies, where individuals who do not respond to surveys at various assessment time points or have missing values on many variables. Inverse probability weighting minimizes potential response bias due to missing data and allows for extrapolation of EAT 2018 data back to the original EAT 2010 school-based sample. Participants who were identified as male, non-white, and having parents with lower educational attainment at 2010 were less likely to respond to the EAT 2018 survey. Weights for inverse probability weighting were therefore derived as the inverse of the estimated probability that an individual responded to the EAT 2018 survey based on several characteristics reported in 2010, including demographics, past year frequency of dieting, and weight status. After weighting, there were no significant differences between the EAT 2018 sample and the full EAT 2010 sample on demographic characteristics, dieting, or weight status (p > 0.9). In the final weighted sample for the present study, 54% were female and 46% were male. Of the final weighted sample, 28.4% were identified as African American or Black, 20.3% White, 20.0% Asian American, 17.1% Hispanic/Latinx, and 14.2% mixed or other ethnicity/race”. Socioeconomic status (SES) was based primarily on baseline parental educational attainment, with 38.9% of participants with low SES, 40.2% were of low-middle/middle SES, and 21.0% were of middle–high/high SES. Because participants were under 18 years of age at baseline but over 18 at follow-up, BMI was assessed via BMI percentiles in adolescence and BMI in emerging adulthood. The average BMI percentile in adolescence was 69.1 (standard deviation [SD] = 27.7%) and the average BMI at emerging adulthood was 27.2 (SD = 7.0).

Measures

The EAT 2018 survey retained key items from the EAT 2010 survey and included several additional items to address areas of new interest [30,31,32,33]. In particular, questions pertaining to WRSM apps were added in the 2018 survey and were defined as smartphone applications or other technologies participants used to manage their weight or behaviors that may affect weight, such as eating and physical activity, by tracking their behaviors (i.e., self-monitoring). Focus groups with 29 emerging adults were used to pretest the EAT 2018 survey. The test–retest reliability of measures was assessed at each time point; at baseline (EAT 2010), test–retest reliability of survey measures was assessed in a diverse sample of 129 adolescents. At follow-up (EAT 2018), test–retest reliability was assessed in a subgroup of 112 emerging adult participants. All measures used in the current analysis can be found in Table 1 with psychometrics, such as test–retest reliability, reported for the relevant year that the measure was assessed.

Table 1 Measures used in the current study examining eating and weight concern and WRSM app use
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Statistical analysis

Analyses were stratified by gender due to previously observed gender differences in associations between WRSM and eating disorder symptoms [9]. Univariate and bivariate statistics were conducted for all WRSM app use outcome variables. To examine associations between sociodemographic variables and derived WRSM app use variables, we utilized Chi-square analyses. Chi-square analysis tested whether prevalence of use for the respective type of WRSM app differed by demographics. Because types of WRSM app use were not mutually exclusive, independent Chi-square tests were run for both physical activity- and dietary-focused app use. The longitudinal relationships were examined using logistic regressions adjusting for ethnicity/race, baseline parental SES, baseline age, and educational/student status at follow-up. Baseline/adolescent SES was included in all models, as SES in adolescence is known to be a predictor of health outcomes in adulthood, irrespective of adult experiences [34]. Models were run with and without adjustment for adolescent BMI to better understand the role of BMI in the longitudinal associations between eating and weight-related concerns and WRSM [11, 35, 36]. Analyses were conducted using SAS version 9.4 and results were considered statistically significant at p < 0.05.

Results

Types of WRSM apps used by emerging adults

Use of any WRSM apps was more common among women (31.7%) than men (20.1%, p < 0.001) (Table 2). All-in-one trackers, or devices that automatically track physical activity and allow for tracking of other weight-related factors (e.g., Samsung Health or wearable devices with accompanying apps like Fitbit), were the most commonly used app (14.7%), followed by physical activity/fitness (e.g., exercise video apps) (7.8%), diet/physical activity combined (e.g., MyFitnessPal) (6.0%), and diet/weight loss (e.g., MyPlate) (4.3%) apps. All-in-one trackers, diet/physical activity combined apps, and diet/weight loss apps were more commonly used by women than men, but there was no significant difference by gender for physical activity/fitness apps. All other WRSM apps were used by less than 5% of men and women.

Table 2 Prevalence of each type of weight-related self-monitoring (WRSM) during emerging adulthood overall and by gender
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When examining types of WRSM app use, 20.0% of participants were found to use a physical activity-focused app (all-in-one tracker and/or physical activity/fitness), with more women (23.2%) than men (16.1%, p < 0.001) reporting use. Dietary-focused app use (diet/physical activity combined and/or diet/weight loss) was less common than physical activity-focused app use in the overall sample (9.3%), but was similarly more common among women (12.5%) than men (5.5%, p < 0.001).

Who uses WRSM apps

Women

WRSM app use was consistently associated with educational/student status (Table 3), such that individuals with a high school degree or less had the lowest prevalence of both physical activity-focused and dietary-focused app use (ps < 0.01). There was also a strong bivariate relationship between BMI category and dietary-focused app use, with 18.7% of participants with a BMI ≥ 30 kg/m2 using dietary-focused apps compared to 9.2% of those with a BMI of 18.5–24.9 kg/m2, and only 3.5% of participants with a BMI < 18.5 kg/m2. WRSM app use did not differ by SES, ethnicity/race, or age.

Table 3 Frequency (%) of weight-related self-monitoring (WRSM) during emerging adulthood by sociodemographics*
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Men

There was also a relationship between WRSM app use and educational/student status among men. Current college students and those who had a bachelor’s or graduate degree had higher prevalence of physical activity-focused app use compared to those who were not currently students or did not have a college degree (p < 0.001). Similarly, those with a bachelor or graduate degree or who were current bachelor or graduate students were more likely to use dietary-focused apps (p = 0.008) than those who with lower educational attainment. There was a significant association between ethnicity/race and physical activity-focused app use (p = 0.004) with the highest prevalences among Hispanic/Latino men (22.4%), and lowest prevalence among mixed/other ethnicity/race (6.9%). There was also an association between SES and dietary focused-app use (p = 0.001), with the highest prevalence of use among high-middle/high SES (10.1%) compared to low SES (3.6%) and low–middle/middle SES (4.1%). Prevalence of dietary self-monitoring use was also lowest among individuals 21–22 years of age (2.9%) compared to those who were 18–20 (8.0%) or 23–30 years of age (9.2%, p = 0.007). There were no associations between WRSM app use and BMI among men.

Relationships between eating and weight-related concerns in adolescence and use of WRSM apps in emerging adulthood

Women

Dietary-focused app use Use of unhealthy weight control behaviors (odds ratio [OR] = 1.81, 95% confidence interval [CI]: 1.14–2.87), engagement in unhealthy muscle-building behaviors (OR = 1.84, 95% CI 1.10–3.08), perceiving oneself to be overweight (OR = 2.22, 95% CI 1.41–3.50), and having a BMI at or above the 85th percentile (OR = 2.11, 95% CI 1.33–3.33) during adolescence predicted greater use of dietary-focused apps in emerging adulthood. Associations were further examined with adjustment for BMI during adolescence and the associations only remained statistically significant for prior unhealthy muscle-building behaviors (OR = 1.73, 95% CI 1.03–2.92).

Physical activity-focused app use None of the eating and weight-related concern measures assessed in adolescence predicted use of physical activity-focused apps 8 years later, irrespective of adjustment for BMI (Table 4).

Table 4 Prospective associations of eating and weight-related measures during adolescence and weight-related self-monitoring (WRSM) 8 years later, by gender (adjusted for age, race/ethnicity, educational/student status, socioeconomic status, with and without adjustment for BMI)
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Men

Dietary-focused app use Other muscle-building behaviors (OR = 2.22, 95% CI 1.09–4.54) and body dissatisfaction (OR = 2.45, 95% CI 1.18–5.07) in adolescence were the only significant predictors of dietary-focused app use in emerging adulthood. In models with additional adjustment for BMI, both other muscle-building behaviors (OR = 2.18, 95% CI 1.07–4.47) and body dissatisfaction (OR = 2.35, 95% CI 1.12–4.92) remained significant predictors of dietary-focused app use.

Physical activity-focused app use Dieting in the last year (OR = 1.65, 95% CI 1.02–2.65), other muscle-building behaviors (OR = 1.63, 95% CI 1.05–2.53) and body dissatisfaction (OR = 1.71, 95% CI 1.09–2.68) in adolescence predicted increased likelihood of using physical activity-focused apps in emerging adulthood, as did having a BMI at or above the 85th percentile (OR = 1.59, 95% CI 1.01–2.50). After adjusting for BMI during adolescence, only the association between prior use of other muscle-building behaviors (OR = 1.60, 95% CI 1.03–2.49) and body dissatisfaction (OR = 1.65, 95% CI: 1.04–2.61) and emerging adulthood use of physical activity apps remained significant.

Discussion

In a community-based sample of emerging adults from diverse ethnic/racial and socioeconomic backgrounds, the present study examined what types of WRSM apps participants used, who used WRSM apps, and whether eating and weight-related concerns in adolescence predicted use of WRSM apps in emerging adulthood. Results indicated that use of physical activity-focused apps was more common than use of other WRSM apps. Furthermore, women were more likely than men to be using WRSM apps. Students and participants who had graduated from college were more likely to use both physical activity- and dietary-focused apps than those with a high school education or who were not students. Among women, many forms of eating and weight-related concerns in adolescence predicted use of dietary-focused app use eight years later. Unhealthy muscle-building behaviors remained a salient predictor of later dietary-focused app use among women after controlling for BMI. Among men, other muscle-building behaviors and body dissatisfaction predicted later dietary-focused app use, irrespective of BMI adjustment. There were no observed associations between eating and weight-related concerns in adolescence and physical activity-focused app use in emerging adulthood among women. However, among men there was evidence that use of other muscle-building behaviors, dieting, body dissatisfaction, and having a higher BMI in adolescence were associated with increased use of physical activity-focused apps in emerging adulthood. Thus, results indicated WRSM apps were common among emerging adults, particularly women, and that eating and weight-related concerns in adolescence may predict dietary self-monitoring app use but be a less salient predictor of physical activity-focused self-monitoring app use.

The present study expands upon prior research examining WRSM app use, which has been conducted primarily among college students [9, 18], by showing that WRSM app use is common among a highly diverse community sample of emerging adults. Notably, education/student status had the most consistent relationship with WRSM app use of any sociodemographic characteristic with the highest level of use among college students and those with a college education. A prior study of college students found no associations between WRSM and parental education, which was similar to our findings across SES in women [9]. However, we found dietary-focused app use to be less common among men of low SES, which may be due, in part, to the cost of certain dietary-focused apps. The present study also found that dietary self-monitoring was more common among women with higher BMI, similar to previous findings among college students [11]. Higher prevalence of dietary self-monitoring among women with higher BMI is not surprising given that WRSM is often recommended to persons with weight-related concerns [6]. It is possible that a portion of women with higher BMI were attempting to lose weight and independently sought out or were introduced to dietary-focused WRSM apps to assist in their attempts at weight loss. Our results indicating that WRSM apps are common among individuals of all SES, ethnicity/race and weight status has important clinical and public health implications. Because WRSM apps are widely used, the potential ramifications of WRSM app use are therefore also widespread and may be impacting vulnerable populations.

One such potential consequence of using WRSM apps is increased eating disorder risk. Among non-clinical samples, there has been a growing body of literature focused on the hypothesis that WRSM app use increases eating disorder risk. However, prior work examining whether WRSM app use increases eating disorder risk in non-clinical populations has, to our knowledge, been exclusively cross-sectional, limiting the ability to understand the directionality of the relationships between WRSM app use and eating disorder risk. It has been hypothesized that eating and weight concerns may actually precede the use of WRSM apps rather than being the results of WRSM [18]. The present study adds to this literature by showing that eating and weight concerns in adolescence may indeed predict the use of WRSM apps in emerging adulthood, particularly dietary self-monitoring apps. However, the relationships between eating and weight-related concerns in adolescence and later WRSM app use are not consistent across genders or by types of eating and weight-related concerns suggesting that these relationships are nuanced and complex. Interestingly, WRSM app use was more common among women as compared to men. That said, there were more consistent associations between eating and weight-concerns in adolescence predicting later WRSM app use among men as compared to women; this finding stands in contrast to the current literature, which shows stronger cross-sectional associations in emerging adulthood among women, as compared to men [37]. There may be many reasons for these seemingly discrepant results. For example, it may be that higher prevalence of WRSM app use in women is a by-product of ubiquitously high eating and weight-related concerns in adolescence or increases in concerns over time, whereas WRSM app use in men may be more indicative of long-standing eating and weight-related concerns, which are less common among men [38]. Future research is needed to disentangle how the relationships between WRSM app use and eating and weight-related concerns vary over time and by gender. Additionally, elevated BMI during adolescence predicted future WRSM app use, and many of the relationships between eating and weight-related concerns and WRSM app use were no longer significant after adjusting for baseline BMI. Because those of higher BMI are more likely to have eating and weight-related concerns and also gain more weight over time, it is also possible that WRSM apps are used in emerging adulthood as a form of weight management. Understanding that individuals who have eating and weight-related concerns may be more likely to use WRSM apps is important in that it contributes to our understanding of who uses WRSM and how the use of WRSM apps might impact those who choose to use them. While the present study takes an important first step toward the complex relationships between eating and weight-related concerns and WRSM app use, future longitudinal research should examine more immediate predictors of use and whether eating and weight-related concerns increase following use of WRSM apps. Clinicians should also be cognizant of the complex relationships between WRSM app use and eating and weight-related concerns and should screen for eating and weight-related concern among those who use WRSM apps. Further, clinicians recommending the use of WRSM apps to their patients should do so with caution until research can determine whether WRSM apps are effective in eliciting beneficial behavior change in the general population, and whether WRSM apps can cause increased eating disorder risk.

The only measure of eating and weight-related concern in adolescence that predicted future dietary-focused app use among both men and women was other muscle-building behaviors. A relationship between muscle-building behaviors and dietary restraint has been demonstrated previously [39]; therefore, it could be that those engaging in muscle-building behaviors choose to engage in dietary restraint, using dietary-focused WRSM apps as a tool to do so. Surprisingly, muscle-building behaviors did not predict physical activity-focused app use among men or women. The lack of association may be a result of the types of physical activity tracked using these apps (e.g., steps, calories burned), in that individuals using muscle-building behaviors are engaging in forms of physical activity that are not generally monitored via apps, such as weightlifting or resistance exercises [40]. Future work is needed to further understand how those engaging in muscle-building behaviors are using dietary-focused apps, and whether there are other forms of physical activity self-monitoring that those using muscle-building behaviors are engaging in.

The current study has many strengths, most notably the longitudinal study design and large and socioeconomically and ethnically/racially diverse population-based sample of emerging adults. Additionally, participants self-generated responses to apps used for managing their eating, activity, and weight, allowing us to build understanding of the breadth of WRSM apps used among the population. However, we had to make some assumptions about types of use as participants reported the WRSM apps that they used and not what features of the WRSM apps that they used. Additionally, because of the lower prevalence of WRSM apps, particularly among men, we may not have been able to statistically detect all associations despite potentially meaningful effect estimates. Further, due to low numbers of gender minorities and the use of gender-stratified analyses, gender minorities were excluded from the present analyses and warrant future research. Moreover, it is possible that there may have been other unmeasured factors that influenced WRSM app use over time such as nutritional knowledge or being introduced to WRSM for health reasons. Future research should examine smaller increments of time and explore unmeasured potential reasons for WRSM app use.

The findings of this study indicate that WRSM apps are popular among emerging adults in general, but more common among women and those with higher educational attainment or who are college students. The present study suggests that eating and weight-related concerns in adolescence may predict use of dietary-focused apps in emerging adulthood, particularly for women, but that BMI may explain many of these associations. Further, eating and weight concerns may not be the most salient predictors of future WRSM app use, but that youth with elevated BMI may be particularly likely to engage in future WRSM. Future research is needed to identify potential mental and physical health consequences of using WRSM apps, particularly whether eating and weight-related concerns increase because of using WRSM apps. Clinicians, parents, and public health professionals should exhibit caution when recommending or encouraging the use of WRSM apps until we are able to further understand the temporality of WRSM app use and negative health consequences.

What is already known on this subject?

Use of weight-related self-monitoring (WRSM) apps is cross-sectionally associated with eating and weight-related concerns. However, little is known whether eating and weight-related concerns in adolescence predict use of WRSM apps in emerging adulthood.

What does the study add?

This study adds valuable information on the longitudinal relationships between eating and weight-related concerns in adolescence predicting increased likelihood of using weight-related self-monitoring apps in emerging adulthood.