Introduction

Childhood obesity is a public health concern. In 2017, 30% of children 5–17 years of age in Canada were classified as overweight or had obesity, putting them at greater risk of chronic diseases including asthma, type 2 diabetes, and heart disease [1]. Low physical activity is one of many risk factors for childhood obesity [2–4]. There is considerable evidence demonstrating an inverse relationship between physical activity and body mass index (BMI) in children [5–7].

The Canadian 24-Hour Movement Guidelines for Children and Youth (5–17 years) recommend that children accumulate 60 minutes of moderate-to-vigorous physical activity and several hours of light physical activity per day [8]. In their 2022 annual Report Card on Physical Activity, a grade of a “D” was assigned to children and youth’s 24 hour movement scores as only 28% of children and youth met the guidelines, a decrease from the last two years [9].

The emergence of the COVID-19 pandemic required public health restrictions to limit the spread of the virus. Temporary cancellations of organized extracurricular activities and closures of schools, and recreation centres were widespread and disrupted daily behaviours, including physical activity and sport participation [10]. A growing body of literature indicates that public health restrictions were associated with a decrease in physical activity and an increase in sedentary time in children [11–16].

While physical activity in children and youth decreased during COVID-19 lockdowns [9, 17, 18], emerging evidence suggests that child weight has increased [12, 14, 19–21]. During the pandemic, longitudinal trends show a doubling in the rate of BMI increase compared to pre-pandemic rates [21] and significant weight gain in school-aged children [20]. Specifically, the longer the duration of school closures and reduced physical activity, the higher the predicted increase in BMI and obesity [11]. The evidence to-date suggests that COVID-19 related weight gain has been most prevalent in children already vulnerable to unhealthy weight gain [14, 19, 21]. Increases in BMI during the pandemic have been observed to be greater for boys and non-Hispanic Black and Hispanic children, than for girls, and non-Hispanic White and Asian children [11, 19]. Boys with pre-existing obesity saw the greatest increase in BMI during lockdowns [14].

Conversely, social restrictions may have caused unexpected weight loss as a result of increased prevalence of eating disorders [22]. Disruption of daily behaviours and routines may have influenced regular coping mechanisms, and depleted healthcare resources may have impacted access to eating disorder resources and treatment options [23]. Electronic health records of 5.2 million individuals, mostly in the United States, indicated that diagnostic incidence of eating disorders increased by 15.3% in 2020 compared with previous years, and occurred primarily in adolescents and people with anorexia nervosa [24].

While evidence is emerging on physical activity and weight change in children during the COVID-19 pandemic, limited literature is available within Canada. Canadians experienced restrictive public health responses to COVID-19 during the first years of the pandemic, including lengthy lockdowns and school closures [25], potentially placing children in Canada at increased risk for unhealthy weight changes and reductions in physical activity. Therefore, the objective of this study was to investigate the association between children’s parent-reported physical activity levels and weight changes during the COVID-19 pandemic among children and youth in Ontario Canada.

Methods

Results

A total of 13,920 participants opened the survey and provided informed consent to participate. Of these, 9% did not respond to any questions and 7% were considered invalid and excluded from analysis (e.g., based on age or region of residence), leaving 11,778 (84%) parents who participated in the study. Of 11,778 participants, 8750 had a child between the ages of 5 and 17 years. Of 8750 parents, a total of 7270 (83%) of parents reported on their child’s weight change over the past year: 6.3% reported that their child had lost more weight than expected, 24.8% reported greater than expected weight gain, and 68.9% reported healthy growth or no weight change (Table 1).

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Table 1. Description of study population (n = 8750).

https://doi.org/10.1371/journal.pone.0292934.t001

Physical activity levels and parent concern about physical activity, overall and stratified by gender, are also presented in Table 1. Per national physical activity guidelines (i.e., 60 minutes of moderate-to-vigorous physical activity per day and several hours of structured and unstructured light physical activity per day [8]), only 13.2% of children engaged in at least 60 minutes of moderate-to-vigorous activity 6–7 days per week, and 57.8% of children engaged in less than 90 minutes of light activity per day. A total of 37.5% of parents reported “a lot” of concern about their child’s physical activity over the past year.

Figs 1 and 2 present the adjusted OR for the associations between physical activity related variables and child weight gain and loss, respectively. Fig 3 presents the adjusted OR for the overall association between physical activity measures and child weight change, inclusive of weight gain and loss. All physical activity variables were strongly associated with child weight gain and loss over the last year (Table 2). For each exposure a consistent ‘dose-response’ was observed such that the fewer minutes per day, days per week of activity, or greater parental concern, the greater the increase in odds of unexpected weight gain or weight loss. For example, compared to children who engaged in at least 60 minutes of moderate-to-vigorous physical activity 6–7 days per week, children who engaged in 0–1 days per week had a 5-fold increase (adjusted OR 5.81; 95% CI 4.47, 7.56) in the odds of weight gain. In all cases, the increase in odds was attenuated once adjusted for confounders.

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Fig 1. Associations between physical activity level exposures and odds of experiencing unexpected weight gain.

Odds ratios were adjusted for parent ethnicity, parent education level, parent difficulty paying bills, housing type, method of school delivery, child age, child gender.

https://doi.org/10.1371/journal.pone.0292934.g001

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Fig 2. Associations between physical activity level exposures and odds of experiencing unexpected weight loss.

Odds ratios were adjusted for parent ethnicity, parent education level, parent difficulty paying bills, housing type, method of school delivery, child age, child gender.

https://doi.org/10.1371/journal.pone.0292934.g002

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Fig 3. Association between physical activity level exposure and odds of experiencing unexpected weight change (weight gain or weight loss).

Odds ratios were adjusted for parent ethnicity, parent education level, parent difficulty paying bills, housing type, method of school delivery, child age, child gender.

https://doi.org/10.1371/journal.pone.0292934.g003

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Table 2. Multinomial logistic regression for the association of physical-activity related variables and child weight gain and loss compared to the reference category of “healthy growth or no change” overall and stratified by gender.

https://doi.org/10.1371/journal.pone.0292934.t002

There was no evidence of a difference in the proportion of unexpected weight gain, loss, or any measure of physical activity between boys and girls (Table 1). Overall, the dose response of increasing odds of unexpected weight gain and loss with decreasing physical activity levels was observed in both girls and boys but the stratified results did not provide strong evidence that the associations differed by gender (Table 2). Further, none of the interaction terms were statistically significant.

Discussion

This study found that over the first year and a half of the COVID-19 pandemic in Ontario, Canada, a high proportion of children did not meet physical activity recommendations and have experienced unexpected weight changes. In this study, 86.8% of children did not meet the physical activity recommendations from the 24-Hour Movement Guidelines of 60 minutes of moderate-to-vigorous activity per day [29]. Our results are consistent with the 2022 ParticipACTION Report Card which reported that 76.2% of children (5–11 years) and 86.8% of youth did not meet the physical activity recommendation at the start of the pandemic in April 2020 compared to 82.5% of children and 88.4% of youth in October 2020 [9]. We also report that 75% of parents were somewhat or very concerned about the physical activity levels of their child. Being very or somewhat concerned about their child’s physical activity levels was strongly associated with unexpected weight gain and loss in children. Previous literature echo these findings, whereby concerned parents typically reported that children were significantly less physically active and the home environment was less supportive of physical activity compared with parents who were unconcerned [30].

The strong associations reported between all measures of physical activity and child weight gain were consistent with findings from a scoping review of pediatric obesity risk factors where irregular vigorous physical activity, low activity during break times at school, limited outdoor playtime and irregular or lack of participation in extracurricular activities were identified as risk factors for childhood obesity [31]. The results of this investigation also showed a strong association between low levels of physical activity and unexpected weight loss. A number of studies have found similar results, where underweight peers had not met physical activity guidelines, or were not necessarily participating in more physical activity then peers with obesity or overweight [32, 33]. Similarly, Ellis et al. (2017) observed that children who were underweight spent more time sitting compared to normal weight and overweight peers [34]. The results of this investigation suggest that physical activity may promote healthy growth in children and youth and is preventative against unhealthy weight loss.

Although previous literature indicates that boys tend to be more active than girls [35], the results of this investigation found that the frequency of outdoor play, light physical activity, and moderate to vigorous activity between boys and girls were very similar. Additionally, our results did not reveal a significant difference in weight gain or loss between boys and girls, despite previous literature reporting that boys more frequently have overweight or obesity than girls [11, 19, 36]. Lastly, there was no significant evidence of a difference in the association between physical activity and weight status between boys and girls. There may not have been differences by gender because boys and girls may have equally been limited by public health restrictions. Data reported by ParticipACTION also showed a reduction in differences between the proportion of girls and boys meeting physical activity recommendations as the pandemic progressed [9].

The strengths of this study include its large and diverse sample, timely data collection, and extensive measures of physical activity. However, there were several limitations. Child parent-reported weight is subject to recall and response biases, including inaccurate recall, misunderstanding of questions and a tendency to respond desirably [37]. Further, the validity of parent-reported measures of child weight change during the pandemic is unknown. Previous studies on child body weight perception indicate that ~44% of parents underestimate their child’s body size, and a majority of parents of children with obesity or overweight underestimate child body size [38, 39]. The magnitude of weight change and child BMI were not captured in this study, so it cannot be determined if parents’ understanding of healthy growth is consistent with child growth standards. Similarly, parent-reported physical activity levels tend to overestimate the actual physical activity behaviours of children [40]. Nevertheless, the exposure of child’s parent-reported physical activity used in this study was taken from a validated national survey [41], and has also demonstrated a weak-to-moderate correlation with accelerometer-measured physical activity in this same group [42].

The cross-sectional study design results in unknown directionality of the associations. While previous literature suggests that physical activity impacts weight change, the reverse effect may also occur, where weight gain makes physical activity more uncomfortable [43]. A pre-pandemic control group was not included in this study; thus, we cannot conclude whether the observed association between physical activity and weight change changed over time. Lastly, the results of this study may not be generalizable. Future studies should utilize a prospective design, include a pre-pandemic control, and use objective measures of weight change and physical activity to further validate the observed associations.

Conclusion

This study found that a large proportion of children experienced unexpected weight gain and weight loss during the COVID-19 pandemic. Further, very few children during this time met physical activity guidelines. Our findings suggest a strong association between physical activity and unexpected weight change during the COVID-19 pandemic in Ontario. Although the association between low physical activity levels and weight gain is well documented, our study suggests reduced physical activity has a similar effect in increasing the odds of weight loss. Our findings contribute to the understanding of the potential impact of the COVID-19 pandemic and associated restrictions on the health and development of children and youth in Canada. Given the high prevalence of reported weight gain and weight loss in children, it is important to monitor child growth post-pandemic and identify predictors of optimal growth in children; this study suggests that interventions focused on improving child physical activity may be one approach to positively support healthy weights in this population.