Background
The prevalence of childhood obesity reaches 20–25% in European countries and its treatment has become a great challenge worldwide [
1]. All recent studies highlight the multidisciplinary approach necessary to tackle this complex and multifactorial health condition [
2,
3]. In 2016, we demonstrated from our cohort that with a specialized multidisciplinary team involving trained doctors, nurses, dieticians, psychologists and physical trainers, we could stabilize and even decrease body mass index (BMI) z-score in 80% cases of children and adolescents with overweight or obesity [
4]. However, in our daily practice, we are confronted to ups and downs due to life events that influence weight gain. For instance, we have long since learned that school-related stress (e.g. due to bullying) [
5] or summer vacations [
6] are punctual risk factors for weight gain in children, as reflected in the literature.
Due to the COVID-19 epidemic that struck the world in 2020, a lockdown has been imposed in Switzerland between March 15th and May 11th 2020. As other obesity specialists [
7‐
9], we hypothesized that the closing of schools and sport clubs, as well as the impossibility of having a regular health monitoring at our clinic, would have a negative influence on the weight of our population of children and adolescents with obesity. Studies in children and adults with obesity have reported changes in lifestyle behaviors during the lockdown, but none monitored their weight [
10‐
14]. Studies that reported weight gain were based on self-reported weight measurements and no standardized/official measures were used [
13,
14].
The aims of our study were to evaluate the effects of the COVID-19 lockdown in spring 2020 on the BMI of children treated for obesity in our clinic, and to compare it to the same period in 2019. Finally, we compared their evolution with that of normal-weight children who were followed for other medical reasons during the same periods.
Discussion
The purpose of this retrospective study was to investigate the effects of the COVID-19 lockdown on BMI on youth with and without obesity.
Indeed, several studies demonstrated that the 2020 lockdown resulted in behavioral and lifestyle changes, especially related to dietary choices and habits as well as in sedentary and physically active occupations [
13,
14]. Subjects with obesity seemed particularly at risk since some studies showed that those changes have caused a weight gain of 1.5 to 3 kg in adults suffering from excess weight [
10‐
12], a phenomenon that some authors have called “covibesity” [
21]. However, to date, no studies have looked at this issue in children. Therefore the aim of our study was to look at the weight evolution during the lockdown period in children and adolescents with obesity regularly followed in our consultation, and to compare the evolution to the same period the previous year. We were also interested to see if normal-weight children followed for other medical reasons experienced the same difficulties as our population.
Normal growth during childhood involves weight gain and height increase, with an average increase of the BMI of 0.3 points every 3 months. In our study, although we did observe a gain in weight and BMI during the 2 studied periods both in normal-weight youth and in those with obesity, the increase was not of the same magnitude between the two groups.
Indeed, during almost a similar interval, subjects with obesity gained almost twice as much weight as normal-weight subjects, whether it be in 2019 or in 2020. This difference may be explained by several factors. First, this finding may simply confirm the tendency of subjects with obesity to gain more weight than normal-weight children, as suggested by Lagstöm et al. [
22]. However, subjects with obesity are known to have more precocious puberty and it is possible that some of them were further along in the puberty process, as might suggest the fact that they grew significantly more (height + 2.6 cm vs. + 0.9 in the control subjects), even after age adjustment. However, since no puberty outcomes were assessed, we can only assume this. Nevertheless, weight gain was more pronounced in the subjects with obesity during the 2020 lockdown period and between 2019 and 2020 with a difference of 1.3 kg, against a difference of only − 0.1 kg in the control group. This difference in weight gain between normal-weight and obese subjects during the lockdown has been already observed in adult studies, with almost identical magnitude of weight gain between the 2 groups as we observed in our study [
10,
23]. Similarly, while the BMI increased in both groups in 2019, this increase was more pronounced during the lockdown in 2020 for children with obesity. The difference of BMI between 2019 and 2020 was of 0.6 points in subjects with obesity compared to a decrease of 0.36 points in the control group. It is interesting to note that in 2019, the BMI change was smaller in the obese than in the control subjects when adjusting for the change in height that was different between the 2 groups. This may confirm the positive impact of specific support for children with obesity, as suggested in other publications [
24‐
26]. Furthermore, our results also suggest that it may be more difficult for children and families dealing with weight concerns to maintain their efforts when the environment and living conditions change drastically, such as during the lockdown we experienced in 2020, especially when no medical follow-up can be provided, as was the case in our hospital.
Another interesting result related to the weight range or BMI changes in our study was that subjects with obesity tended to display more extreme changes than controls, especially in 2020. Some patients took advantage of this special circumstance to improve their diet and spend more time exercising, losing as much as 10 kg, while others were unable to stick to our recommendation, gaining up to 18 kg of weight. This may reflect the difficulties encountered by our population suffering from obesity to regulate their weight. The subjects who lost the most weight were older than the others and one explanation could be that adolescents no longer had the possibility to buy fatty and sugary foods after school or during their lunch break. Not surprisingly, the ones who put on the most weight had a longer interval between medical visits. This can have several explanations. First, it is known that motivation lasts only a few weeks and that it may be difficult to maintain an effort when medical appointments are as far apart as 6 months. Secondly, children who knew they had gained weight might have delayed their visit after the end of lockdown in an attempt to stabilize their weight before their next appointment. They might also have been afraid of catching the COVID-19 disease on their way to the hospital using public transports or during their medical visit. Stress being generally recognized as a risk factor related to excessive weight [
27], it is possible that anxious patients were negatively impacted by pandemic-related stress, which might have caused, among other consequences, eating disorders to appear or worsen [
28‐
30]. Normal-weight children did not show such extreme changes, as they probably struggled less with food choices or quantities and were more prone to move even when their usual physical activities were cancelled.
This study has some limitations. First, the sample size is small and we could probably have seen a more significant difference between the groups if it had been larger. However, to date, no other study has actually measured and compared weight as precisely at 2 years interval. Secondly, we did not look at the relationship between weight and lifestyle changes in the present study, however, we investigated this outcome in a group of adolescents in different study which results will be published soon (manuscript submitted). Finally, the normal-weight group was composed of children with medical health conditions and not healthy ones, which may have influenced their weight evolution. However, this bias was minimized when we compared 2019 to 2020 in the same children. Furthermore, we excluded underweight children to ensure that seriously ill patients were not included in the sample and we controlled the normal staturo-weight evolution of the selected subjects to make certain that their disease had no significant impact on it. Besides, the vast majority of our subjects were suffering from minor afflictions such as chronic cough, reflux or constipation, conditions on which the lockdown would not have had much influence.
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