During the pandemic, many children gained weight – but most bounced back

Peter had always been slim and agile – until the COVID-19 pandemic hit in 2020 and shut everything down. From eating healthily and playing football in the schoolyard every day, he now had to stay at home, where everyday life quickly fell apart and he ended up spending hours sitting still in a chair. School and entertainment moved to the screen, where he spent his days gaming and eating large amounts of pizza. This caused his weight to shoot up in record time.

And he was far from the only one whose weight was challenged during the pandemic. A comprehensive study from Denmark, recently published in JAMA Network Open, documents that the vast majority of children experienced significant shifts in their BMI during this period – across all age groups.

Children’s weight is usually stable – but the pandemic disrupted that pattern

The study’s first author is Frederik Kirkemann Jensen, a master’s student in public health. He arrived at the results by performing statistical calculations on data from 426,935 children from Denmark’s unique health registers. He carried out the work in collaboration with Jens Meldgaard Bruun, Professor at Steno Diabetes Center Aarhus and Aarhus University as well as the Danish National Center for Obesity.

The data comes from the national paediatric examinations conducted by community health nurses in schools and registered in the Danish Children’s Database. The researchers selected data from children aged 6 to 14 years who had their BMI measured at least once before, during and after the pandemic. These were compared with a predictive model based on 2010–2019 data, showing how a child’s BMI would likely have developed without the pandemic. Comparing with the expected trend enabled the researchers to isolate the effect of the pandemic.

“The analysis shows a clear increase in children with overweight and obesity during the pandemic,” explains Jens Meldgaard Bruun. “Fortunately, the vast majority returned to a healthier weight during the first year after society reopened. Unfortunately, we found a worrying exception in the youngest schoolchildren, who had difficulty in losing the extra kilos.”

We will come back to them.

These two researchers are convinced that the pandemic triggered the shifts in children’s BMI. When they look at the 10 years before the pandemic, Danish children’s weight curves were stable, with a consistent distribution of children across the weight classes – a characteristic picture that suddenly shifted significantly during the pandemic. The researchers consider this as a sign that the pandemic clearly but temporarily affected children’s weight – and that most children returned to their normal weight as soon as everyday life returned.

The youngest children struggle the most with obesity

Although this accurately describes the vast majority of children, one group of children stands out: primary school children. Here, the proportion of obese children only fell part of the way back to the original level. One year after the reopening, significantly more primary school children were still overweight than before the pandemic. The researchers do not yet know why this group in particular stands out. This may be because younger children are more dependent on their parents in everyday life. If the parents are inactive and eat unhealthy food, so do the children.

“If the young children gain weight because of this, the children with genetic vulnerability have more difficulty in losing the weight again, since this typically requires that the parents significantly change the family lifestyle,” says Jens Meldgaard Bruun.

Mental well-being plays a big role in weight

Maintaining a healthy weight largely comprises having the energy to pay attention to what you eat and how much you exercise. But it also involves your mental energy – whether you are mentally balanced and feeling good. This is where children were particularly challenged during the pandemic, since they both lost the structure that normally keeps them organised and were left to their own devices. As a result, they had to find ways to keep their spirits up without the usual support from their network. According to the researchers, this increased the risk of loneliness – and with it, anxiety and depression.

“Some children were not doing very well at home during the pandemic – not because the parents did anything wrong but because the whole situation created a sense of meaninglessness and uncertainty,” Jens Meldgaard Bruun notes.

He explains that children who are under mental pressure often gain weight. This is well known from studies of vulnerable children who stay at Denmark’s Christmas seal homes (Julemærkehjemmene) – homes that aim to give their well-being a major boost. This is achieved by improving their diet, increasing physical activity and helping them connect with other children who face similar challenges.

The pandemic disrupted children’s daily lives and community

Seen in this light, the pandemic can be seen as a bodily reaction to mental pressure – and this raises the question of whether current major societal crises such as the war in Ukraine, the conflict around Gaza and the unresolved climate crisis can create similar reactions among children.

But Jens Meldgaard Bruun doubts that they can. As long as children can go to school, see their friends and participate in sports and play, their basic well-being is preserved – even if the world around them is in turmoil.

“The COVID-19 crisis was special because it directly cut children off from their everyday lives. It was not just something that happened on TV – it shut down their school, after-school activities and communities. It directly disrupted their everyday lives. But we have seen children react similarly during long-term teacher strikes and major school reforms,” he points out.

Lack of knowledge about what makes some children more vulnerable

But if the pandemic caused such large swings in children’s BMI, what made some children more vulnerable than others? That question remains unanswered. The study provides important insights into what happened – but not why. Factors such as parental BMI, mental well-being at home and genetic vulnerability are still unknown.

“We could only adjust for education and income and not for the overall health profile of the family. We would have liked to, but we did not have that option here,” says Jens Meldgaard Bruun.

He calls for more research into how psychosocial factors affect children’s health behaviour – both in normal everyday life and under pressure. In particular, he sees a need for more knowledge about children’s ability to regulate emotions and their sense of safety and community at home. Jens Meldgaard Bruun emphasises that the current registry data do not tell the whole story, which is why the research group plans to include questionnaire data and qualitative data in future studies that could also involve other disciplines such as psychologists and anthropologists.

“We need to understand the mechanisms that make some children more resilient than others – and find ways to support those who have the most difficulty in getting back on track. This study reminds us how closely children’s mental and physical health are linked and how important it is to see them as a whole,” he concludes.