Research addressing the impact of the COVID-19 pandemic on psychosocial well-being and health behavior is accumulating; however, implications for emerging adult populations are underexplored. This ...

Objective: To estimate associations of residential mobility with body mass index (BMI), physical activity, and diet and whether associations differ across demographics. Design: Longitudinal cohort with 4 waves of survey follow-up over 15 years. Participants and Setting: A total of 2,110 adolescents and young adults originally from the Twin Cities of Minnesota responded to at least 2 waves of follow-up, beginning at ages 15 to 23 years. Main Outcome Measure(s): Self-reported BMI, physical activity, fast food consumption, breakfast frequency, sugary drink consumption, fruit and vegetable consumption, and screen time. Analysis: Each outcome was modeled as a continuous variable using hierarchical linear regression. Residential mobility—change in residential address—was the main effect of interest. Models adjusted for demographics, marriage during follow-up, and previous level of the outcome. Inverse propensity weights accounted for loss to follow up. Results: No weight-related outcomes differed between movers and nonmovers in the whole sample. When examining effect modification by age, as participants aged, moving was increasingly associated with improvements in weight-related outcomes, particularly BMI. Conclusions and Implications: Results suggest that moving may be associated with poorer weight-related outcomes during a brief window from late teens and early-20s and less associated with weight-related outcomes in the mid-20s and 30s.

between 15e17-years old had stopped gender-affirming medications compared with 10.6% of patients who started GnRHa between 9e14-years, though this difference did not reach statistical significance. Insurance sponsor's rank (family income), birth-assigned sex, and the presence of mood disorders were not associated with cessation rates. Within 2 years of starting GnRHa, 83.2% (95%CI: 70.2 e 94.4%) of patients had started gender-affirming hormones; within 8 years of starting GnRHa, this number increased to 91.6% (95%CI 81.6 e100%). Younger patients had a greater delay in starting gender-affirming hormones. Insurance sponsor's rank, birth-assigned sex, and the presence of mood disorders were not associated with initiation of gender-affirming hormones. Conclusions: Contrary to concerns, GnRHa use did not inevitably lead to use of gender-affirming hormones. One out of twelve TGD adolescents who started GnRHa to address gender dysphoria subsequently stopped treatment. Sources of Support: None. Purpose: StRONG was a multicenter randomized clinical trial of refeeding in hospitalized adolescents and young adults with malnutrition secondary to anorexia nervosa (AN) and atypical anorexia nervosa (AAN) (ClinicalTrials.gov #NCT02488109). At end-of-treatment, higher calorie refeeding (HCR) was more efficacious and less costly than lower calorie refeeding (LCR). Here we compare efficacy of HCR in AAN vs. AN. Methods: Participants were N¼120, 12-24 yr-olds with > 60% median Body Mass Index (%mBMI) and medical instability. AAN was defined as %mBMI >85% at baseline. Meal-based HCR began 2000 calories/day (kcal/d) and advanced 200 kcal/d; LCR began 1400 kcal/d and advanced 200 kcal every other day (no tube feeding). Efficacy was defined as time to restore a 6-point Medical Stability Index (MSI): heart rate (HR) 45 bpm; systolic blood pressure (SBP) 90 mmHg, temperature 35.6 C, orthostatic increase in HR 35 bpm and decrease SBP 20 mmHg, and 75% median BMI (%mBMI). Main outcome was days to restore MSI, compared between groups with unpaired t-test. Exploratory moderator analyses examined the interaction between refeeding treatment and diagnosis on key outcomes (time to recover heart rate and weight gain). Weight gain was defined as change in %mBMI. Results: Modified intention to treat analyses included N¼111. Mean age was 16.5 (2.5) yrs, 43% had AAN. Upon admission, %mBMI was 95.2 (9) in AAN vs. 76.5 (5.9) in AN, p<.001. Upon discharge, %mBMI was 98.3 (8.9) in AAN vs. 82.2 (5.3) in AN, p<.001. MSI was restored fastest in patients with AN refed by HCR [7.1 (5.4) days], whereas medical stability required three additional days to restore in patients with AAN [10.1 (5.3) days, p<0.01]. Diagnosis (AAN or AN) and treatment (HCR or LCR) interacted to weaken the effect of refeeding on HR recovery [B¼3.76 (.572,6.95), p¼0.021] and weight gain [B¼039 (.006,072), p¼0.021], which was 0.3% mBMI per day slower (p¼0.005) and 2.6% mBMI less overall (p¼0.009) in AAN than AN. Conclusions: While HCR is more efficacious than LCR for refeeding in AN, it may contribute to underfeeding in AAN. source) and four family variables (family functioning , parental connection, parental monitoring, and parental psychological control). The outcome, UWCB (e.g. fasting, vomiting, laxative use), was self-reported by young adults eight years later. Logistic regression models estimated odds ratios (OR) and 95% confidence intervals (CI) of UWCB for four weight stigma predictors and four family predictors. Models were adjusted for sociodemographic characteristics, baseline UWCB, and baseline BMI percentile, and predictors were modeled separately. Results: In analyses adjusted for sociodemographic characteristics, all weight stigma and family variables during adolescence longitudinally predicted significantly higher odds of UWCB eight years later. After additionally adjusting for baseline UWCB and baseline BMI percentile, two weight stigma variables (weight teasing from family [OR: 1.42, 95% CI: 1.08, 1.87] and hurtful weight-related comments from family [OR: 1.34, 95% CI: 1.06, 1.70]) and one family variable (poor family functioning [OR: 1.44, 95% CI: 1.14, 1.81]) remained significantly associated with subsequent UWCB. Conclusions: Findings indicate that there are long-term consequences , across major development periods, of weight teasing from family, hurtful weight-related comments from family, and low family 2022 SAHM Annual Meeting / Journal of Adolescent Health 70 (2022) S1eS32 S11

Background: Much of the research to-date on food parenting has evaluated typical use of various parent feeding practices via questionnaire. The Real-Time Parent Feeding Practices Measurement survey was developed for use within an Ecological Momentary Assessment (EMA) protocol to capture momentary use of parent feeding practices in real-time. Methods: This manuscript describes the development of the EMA-based Real-Time Parent Feeding Practices survey and highlights initial descriptive data on the real-time use of 22 individual parent feeding practices (e.g., pressure-to-eat, guided choices, etc.) as reported via EMA by parents of preschool-aged children (n = 116) over a 10-day data collection time period. A total of 3382 eating occasions were reported, with an average of 29.2 reported eating occasions per participant. Results: Results revealed that most participants used a variety of food-related parenting practices day-to-day that span four higher-order domains: structure, autonomy support, coercive control and indulgence. Supportive feeding practices, defined as those from the structure and autonomy support domains, were reported most frequently, with one or more structure behavior (e.g., specific mealtime rules/routines) was used at 88.9% of reported eating occasions and one or more autonomy support behavior (e.g., involvement of the child in meal preparation) was used at 87.3% of eating occasions. While unsupportive feeding practices, defined as practices from within the coercive control (e.g., pressure-to-eat) and indulgent (e.g., anticipatory catering) feeding domains, were reported less frequently, one or more behaviors from each of these domains were still reported at over 25% of all eating occasions. Conclusions: Results of the current study take a next step towards deepening our understanding of the use of a broad range of food-related parenting practices in real-time. Findings revealed that the vast majority of practices used by parents fall within the structure and autonomy support domains. However, most parents did not exclusively use supportive or unsupportive practices, rather they used a combination of food-related parenting practices across all domains. Future research should continue to explore a broad range of food-related parenting practices and seek to understand how parent approaches to feeding are associated with long-term child outcomes, including dietary intake, food preferences, and eating patterns.

This study aimed to identify patterns of change in muscle-building behaviors from adolescence to emerging adulthood and determine what adolescent factors predict new-onset muscle-building behavior in emerging adulthood. Prospective cohort data from a diverse sample of 1,535 participants followed from adolescence (baseline, Mage = 14.4 ± 2.0 years) to emerging adulthood (follow-up, Mage = 22.1 ± 2.0 years) from the population-based EAT 2010–2018 (Eating and Activity over Time) study were analyzed. Changes in muscle-building behavior were identified (starting, stopping, persistent use, or never use). Log-binomial regression models examined adolescent predictors of starting (i.e., new-onset) muscle-building behaviors in emerging adulthood. Prevalence of any use in adolescence (EAT 2010) and/or emerging adulthood (EAT 2018) was 55.1% (males) and 33.0% (females) for protein powder/shakes, 6.7% (males) and 5.4% (females) for steroids, and 19.4% (males) and 6.5% (females) for other muscle-building substances (e.g., creatine, amino acids). In particular, 22.6% (males) and 13.7% (females) started protein powder/shakes, 2.2% (males) and 1.0% (females) started steroid use, and 9.0% (males) and 2.0% (females) started other muscle-building substances during emerging adulthood. Adolescent protein powder/shake consumption was associated with starting steroids/other muscle-building substances use in emerging adulthood in males (adjusted risk ratio [ARR] 2.09, 95% confidence interval [CI] 1.29–3.39) and females (ARR 4.81, 95% CI 2.01–11.48). Adolescent use of protein powders/shakes may lead to a two- to five-fold higher risk of new use of steroids and other muscle-building products in emerging adulthood. Clinicians, parents, and coaches should assess for use of muscle-building behaviors in adolescents and emerging adults and discourage use of harmful products.

Healthcare professionals may motivate their patients to exercise to lose weight, but it is unknown how weight-focused motivations influence young peoples’ PA trajectories. Purpose To examine if weight-motivated exercise predicts moderate-to-vigorous physical activity (MVPA) from adolescence to adulthood in a population-based sample and if this relationship differs by age and body mass index (BMI). Methods Participants (N = 1,428; 13–18 years at baseline; 48.6% female; 49.0% white) responded to surveys in the 15-year longitudinal study, Project EAT (Eating and Activity in Teens and Young Adults). Weight-motivated exercise was examined as a predictor of MVPA across the life course at five-year intervals using linear regression generalized estimating equations and adjusting for demographics (age modeled continuously), BMI (modeled continuously), weight-related intentions, and prior MVPA. Results Weight-motivated exercise predicted higher subsequent MVPA at five-year intervals among females (B = .57, 95% CI:0.13, 1.00) but not males (B = .31, 95% CI:-.09, .72). The association differed by BMI in females (p = .02); weight-motivated exercise was associated with higher subsequent MVPA at lower BMI but lower subsequent MVPA at higher BMI. The association also differed by age in males (p = .008), such that older males who reported weight-motivated exercise had higher subsequent MVPA, whereas this association was not present in younger males. Conclusion Weight-motivated exercise may have a deleterious influence on MVPA for females with higher BMI and may have an advantageous influence on older males. Understanding how motivations for exercise may influence PA trajectories can inform PA promotion over the life course by providing more nuanced guidance by age, BMI, and sex.

Adverse experiences, such as childhood abuse and other violence victimization, are associated with problematic eating. However, whether different types of adversity relate to both maladaptive and adaptive eating behaviors is unclear. This study examined the associations of different adverse experiences with maladaptive (i.e., overeating and binge eating) and adaptive (i.e., intuitive eating and mindful eating) eating by gender. Data were derived from the EAT-2018 (Eating and Activity over Time) study (N = 1411, aged 18–30 years in 2017–2018). Modified Poisson regressions were used to examine the associations between adverse experiences and the prevalence of maladaptive eating. Linear regressions were used to examine the associations between adverse experiences and adaptive eating scores. Each adverse experience was associated with greater prevalence of maladaptive eating and lower adaptive eating scores. Among women, intimate partner sexual violence was strongly associated with more overeating (PR = 2.1 [95% CI = 1.4–3.1]) and binge eating (PR = 2.4 [95% CI = 1.5–3.9]), and less mindful eating (β = −0.6, [95% CI = −0.8, −0.3]); being attacked, beaten, or mugged was most associated with less intuitive eating (β = −0.5, [95% CI = −0.8, −0.2]). Among men, being attacked, beaten, or mugged was strongly associated with more overeating (PR = 2.1 [95% CI = 1.2–3.5]) and binge eating (PR = 3.2 [95% CI = 1.6–6.5]); intimate partner physical violence was strongly associated with less intuitive eating (β = −0.6, [95% CI = −0.9, −0.2]); childhood emotional abuse was strongly associated with less mindful eating (β = −0.8, [95% CI = −1.0, −0.5]). To improve eating behaviors, adverse life experiences and the potential impact on maladaptive and adaptive eating should be considered.

Background: We investigated the percentage of insufficiently active adolescents who became young adults meeting moderate to vigorous physical activity (MVPA) guidelines. We also explored adolescent psychosocial and environmental factors that predicted MVPA guideline adherence in young adulthood. Methods: Participants included N = 1001 adolescents (mean age = 14.1 y) reporting < 7 hours per week of MVPA and followed (8 y later) into young adulthood through Project EAT. We examined mean weekly hours of MVPA, MVPA change between adolescence and young adulthood, and the proportion of participants meeting MVPA guidelines in young adulthood. With sex-stratified logistic regression, we tested 11 adolescent psychosocial and environmental factors predicting meeting MVPA guidelines in young adulthood. Results: Overall, 55% of insufficiently active adolescents became young adults meeting MVPA guidelines. On average, participants reported 3.0 hours per week of MVPA, which improved to 3.8 hours per week in young adulthood. Among female participants, higher MVPA in adolescence and stronger feelings of exercise compulsion predicted greater odds of meeting adult MVPA guidelines (odds ratioMVPA = 1.18; odds ratiocompulsion = 1.13). Among female and male participants, perceived friend support for activity in adolescence predicted greater odds of meeting adult MVPA guidelines (odds ratiofemale = 1.12; odds ratiomale = 1.26). Conclusions: Insufficiently active adolescents can later meet adult guidelines. Interventions that increase perceived friend support for activity may benefit individuals across development.

This study aimed to evaluate the influence of the COVID-19 pandemic on food parenting practices used by parents of young children. Ecological Momentary Assessment (EMA) was used to evaluate parents’ use of coercive, indulgent, structured, and autonomy supportive food parenting practices before and during the COVID-19 pandemic among a diverse racial/ethnic sample (n = 72) of parents of preschool-aged children. The impact of parent and child mood/behavior on use of specific food parenting practices was also evaluated during both time periods. Results revealed that most parents of preschoolers use a variety of food parenting practices, including coercive control, indulgence, structure, and autonomy support practices. The use of structured and autonomy supportive practices, however, decreased during the COVID-19 pandemic. Further, the types of practices used by parents were contextually associated with the mood of the parent as well as child mood. Parent negative mood during COVID-19 was associated with higher levels of coercive control and indulgence and lower levels of structure, whereas child positive child mood was associated with greater use of autonomy supportive practices. These findings suggest that effects of the COVID-19 pandemic on family dynamics around feeding young children include shifts away from theoretically supportive approaches to parenting and highlight the roles of parent and child mood/behavior as potentially important momentary influences on food parenting during this time. Public health practitioners and clinicians working with parents of young children during COVID-19, and in years to come, should consider the potential impact of parental mood and stress, as well as child mood and behaviors. Additional research is needed to better understand how to best help parents maintain supportive feeding practices in the face of challenging situations.

Objectives: This study examines motivations for yoga and identifies unique motivational profiles among a sample of young adult yoga practitioners. This study further determines how young adult yoga...

Weight stigma is prevalent among young people and harmful to health. The current study used a health equity lens to examine cross-sectional and longitudinal associations between experiencing weight teasing (a form of weight stigma) with a range of weight-related health behaviors and weight status in an ethnically/racially and socioeconomically diverse sample of young people. We also assessed whether ethnicity/race and adolescent socioeconomic status (SES) operated as effect modifiers in these relationships. Adolescents (n = 1568) were enrolled in EAT 2010–2018 (Eating and Activity over Time) and followed into young adulthood. Weight teasing; screen time; moderate-to-vigorous physical activity (MVPA); sleep duration; breakfast frequency; fruit, vegetable, sugar-sweetened beverage (SSB), and fast-food intake; and body mass index (BMI) were assessed at baseline (mean age = 14.4&nbsp;years) and eight-year follow-up (mean age = 22.2&nbsp;years). Multivariate linear regression estimated marginal means and 95% confidence intervals. All analyses adjusted for BMI and sociodemographic characteristics. Weight teasing was cross-sectionally associated with longer screen time, shorter sleep duration, and higher BMI during adolescence; and cross-sectionally associated with shorter sleep duration, lower breakfast frequency, higher fast-food intake, higher SSB intake, and higher BMI during young adulthood. In the longitudinal analyses, weight teasing was not associated with health behaviors but did predict higher BMI (teased: 28.2&nbsp;kg/m2, not teased: 26.4&nbsp;kg/m2, p &lt; 0.001). White and higher adolescent SES subgroups had higher MVPA, more frequent breakfast intake, lower fast-food intake, and lower BMI than their respective counterparts. The relationships between weight teasing and health behaviors and weight status were largely consistent across ethnic/racial and adolescent SES subgroups. Findings add to growing evidence that weight-based mistreatment poses a threat to weight-related health and that young people across ethnic/racial and SES subgroups are vulnerable to the negative effects of weight teasing. Limitations include attrition at follow-up and the self-reported nature of many measures. Results suggest a need for increased attention to existing recommendations to reduce weight stigma in young people from diverse ethnic/racial and socioeconomic backgrounds including training for healthcare providers to better equip them to address the harms of weight teasing and foster more compassionate care to promote health-supporting behaviors in young people.

Objective: Disordered eating behaviors (DEBs) have long-term, deleterious effects on health and are more prevalent among socially marginalized groups, likely as a result of systemic inequities across social determinants of health (SDoH). This exploratory study aimed to identify subgroups of emerging adults characterized by main and interactive associations between SDoH and two forms of DEB (binge eating, extreme unhealthy weight control behaviors). Method: Participants (n = 1568; age 22.2 ± 2.1 years) from the United States were drawn from the EAT 2010-2018 longitudinal study. Conditional inference tree (CIT) analyses derived main and intersecting SDoH related to DEB across 33 input variables collected during adolescence and emerging adulthood. Results: The binge eating CIT revealed five subgroups (prevalence: 6.3-23.2%) shaped by variables collected during emerging adulthood: appearance-based teasing (p < .001), financial difficulty (p = .003), gender (p < .001), and everyday discrimination (p = .008). The CIT results for extreme unhealthy weight control behaviors derived six subgroups (prevalence: 2.3-45.5%) shaped by weight teasing (p < .001) and gender (p < .001) during emerging adulthood and public assistance (p = .008) and neighborhood safety (p = .007) in adolescence. Discussion: This exploratory study revealed distinct subgroups of emerging adults with varying DEB prevalence, suggesting that variability in DEB prevalence may be partially explained by intersecting SDoH during adolescence and emerging adulthood. Hypothesis-driven research and replication studies are needed to further explore the associations between SDoH and DEB during emerging adulthood. Public Significance Statement: Disordered eating behaviors are common among young people in the United States and have long-term health consequences. This exploratory study identified subgroups of young people, characterized by combinations of social inequities (e.g., financial difficulties, teasing). Results highlight high-risk

Emerging evidence suggests a cross-sectional association between food insecurity (FI) and disordered eating among adults, while evidence among adolescents is limited. Longitudinal research is needed to elucidate the temporality of this relationship and clarify whether the association differs by age. Three waves of prospective data came from 1813 participants in the Project EAT (Eating and Activity in Teens and Young Adults) cohort study. Data were collected at five-year intervals, with the baseline survey in 1998–1999 (EAT-I; Mage = 14.9 years) and follow-up surveys in 2003–2004 (EAT-II; Mage = 19.5 years) and 2008–2009 (EAT-III; Mage = 24.9 years). Severe FI was assessed as any past-year hunger with one item from the U.S. Household Food Security Survey Module, and a range of disordered eating behaviors were self-reported. Associations adjusted for sociodemographic characteristics were examined with generalized estimating equations. Effect modification by age was also tested. Cross-sectionally, severe FI was significantly associated with greater prevalence of all disordered eating behaviors examined, with the strongest associations observed for extreme weight-control behaviors (prevalence ratio [PR] = 1.49, 95% confidence interval [CI]: 1.13–1.95) and binge eating (PR = 1.49, 95% CI: 1.04–2.12). Longitudinally, severe FI significantly predicted 1.41 (95% CI: 1.05–1.90) times greater prevalence of binge eating five years later after accounting for prior binge eating. Effect modification by age indicated a stronger cross-sectional association between severe FI and unhealthy weight-control behaviors among younger participants. Results support a cross-sectional link between severe FI and disordered eating and provide longitudinal evidence suggesting severe FI is a risk factor for binge eating.

Objective: Digital technology use and muscle-building behaviors reflect a wide range of behaviors with associated health risks. However, links between digital technology use and muscle-building behaviors remain unknown and this study aimed to address this gap. Method: Data were collected from a diverse sample of 1,483 young adults (mean age 22.2 ± 2.0 years) participating in the population-based Eating and Activity over Time 2018 study. Gender-stratified-modified Poisson regression models were used to determine cross-sectional associations between three types of digital technology use (screen time, social media, weight-related self-monitoring apps) and five types of muscle-building behaviors (changing eating, exercise, protein powders/shakes, pre-workout drinks, steroids/growth hormone/creatine/amino acids) in young adulthood, adjusted for sociodemographic characteristics and body mass index. Results: Screen time and social media were either not found to be associated with muscle-building behaviors or in a few instances, associated with less use of these behaviors (e.g., screen time and pre-workout drinks in men). In contrast, the use of weight-related self-monitoring apps was positively associated with all muscle-building behaviors, including steroids/growth hormone/creatine/amino acids in men (prevalence ratio [PR] = 1.83; 95% confidence interval [CI]: 1.13–2.97) and women (PR = 4.43; 95% CI: 1.68–11.68). Discussion: While most recreational screen time may represent sedentary behaviors not related to muscle-building behaviors, weight-related self-monitoring apps are highly associated with more muscle-building behaviors and could be a future target for interventions to discourage the use of steroids and other harmful muscle-building substances.

Various types of stressors are associated with maladaptive eating, but how the stressor of everyday discrimination (e.g., less respect, poorer service) relates to maladaptive eating and adaptive eating remains unclear. We examined everyday discrimination as a predictor of maladaptive and adaptive eating. Data were collected in a population-based study, Eating and Activity over Time (N = 1410, ages 18–30). Everyday discrimination was categorized as none, low, moderate, or high. Outcomes included maladaptive eating (i.e., overeating and binge eating) and adaptive eating (i.e., intuitive eating and mindful eating). Modified Poisson regressions estimated the prevalence ratios (PRs) for overeating and binge eating associated with everyday discrimination. Linear regressions estimated associations between everyday discrimination and intuitive and mindful eating scores. After adjustment for age, ethnicity/race, gender, and socioeconomic status, moderate and high levels of discriminatory experiences were each associated with a significantly greater prevalence of binge eating (PR = 2.2, [95% CI = 1.3–3.7] and PR = 3.1, [95% CI = 2.0–4.7], respectively) and lower intuitive (β = −0.4, [95% CI = −0.7, −0.2] and β = −0.5 [95% CI = −0.8, −0.3], respectively), and mindful eating scores (β = −0.3, [95% CI = −0.6, −0.1] and β = −0.5 [95% CI = −0.8, −0.3], respectively) compared to young adults with no discriminatory experience. Public health efforts to prevent maladaptive eating and encourage the adoption of adaptive eating should consider the potential contribution of everyday discrimination and the need to advocate for equity and inclusion.

Purpose: Growing evidence indicates that experiencing household food insecurity during adolescence is associated with disordered eating and elevated body mass index (BMI). However, little is known about the temporal nature of these relationships. The current longitudinal study examined how adolescent experiences of household food insecurity are related to disordered eating and weight status 8 years later. Methods: A population-based sample of ethnically/racially and socioeconomically diverse participants (n = 1,340) were surveyed as adolescents (mean age = 14.5 years) and as young adults (mean age = 22.0 years). Parents/caregivers completed the six-item U.S. Household Food Security Survey Module at baseline. Results: Household food insecurity was common at baseline (37.8% of sample). In analyses adjusted for ethnicity/race and parental education, adolescent food insecurity longitudinally predicted a higher new onset of binge eating (food insecure: 21.3% vs. food secure: 16.2%, p = .038) and BMI ≥30 kg/m2 (food insecure: 15.9% vs. food secure: 11.0%, p = .024), but not unhealthy weight control behaviors in young adulthood. The majority of adolescents with unhealthy weight control behaviors and elevated BMI still had these problems in young adulthood, but persistence was not associated with adolescent household food insecurity for any outcome. Discussion: Results of this longitudinal study suggest that household food insecurity during adolescence is a risk factor for disordered eating and elevated BMI in young adulthood, highlighting a need to comprehensively address these intersecting problems.

Use of weight-related self-monitoring (WRSM) apps is common among emerging adults, as are weight and shape concerns. The present study aimed to examine (1) whether emerging adult use of dietary-focused (e.g., MyFitnessPal) and physical activity-focused (e.g., Fitbit) WRSM apps was associated with weight-control and muscle-building behaviors, including commonly recommended/conventional behaviors and disordered behaviors and (2) whether prior use of weight-control and muscle-building behaviors in adolescence might explain such relationships. Data were collected as part of the EAT (Eating and Activity over Time) 2010–2018 study (n = 1446) and analyzed using gender-stratified logistic regression models adjusted for demographic characteristics and body mass index. Among women and men, physical activity- and dietary-focused app use were associated with greater adjusted prevalence of disordered weight-control behaviors (e.g., fasting, purging), and disordered muscle-building behaviors (e.g., using steroids). Physical activity- and dietary-focused app use were also associated with a higher adjusted prevalence of commonly recommended weight-control and conventional muscle-building behaviors (e.g., exercising, changing eating habits), but only among those who were also engaging in disordered behaviors. The observed associations remained statistically significant in models that further adjusted for adolescent use of the respective behaviors. Findings suggest that emerging adults who use physical activity- and dietary-focused WRSM apps are more likely to engage in disordered weight-control and muscle-building behaviors and that associations are not explained by engagement in these behaviors during adolescence. Future research is needed to examine if there are aspects of WRSM apps that could be modified to reduce potential harm.