Overweight and obesity are pathologies marked by an increase in body fat as a consequence of a positive energy balance, when the energy intake exceeds energy expenditure over a prolonged period. Obesity in children is considered the main childhood health problem in European countries. In 2010, based on the International Obesity Task Force (IOTF) definitions and the WHO’s Childhood Obesity Surveillance Initiative, it was estimated that about 25 % of European children (aged 6–9 years) were overweight or obese(Reference Wijnhoven, van Raaij and Spinelli1). A recent systematic review and meta-analysis observed a high prevalence of childhood overweight and obesity with a trend for stabilisation in most European countries(Reference Garrido-Miguel, Cavero-Redondo and Álvarez-Bueno2). Paediatric obesity and related consequences on physical, social and psychological parameters have been widely demonstrated(Reference Hruby, Manson and Qi3). In addition, the persistence of paediatric obesity into adulthood can lead to increased morbidity from type 2 diabetes, CVD and cancer, and increased early mortality(Reference Llewellyn, Simmonds and Owen4). While the prevalence of overweight and obesity has been studied broadly, data on the prevalence of underweight are scarce and limited. Nevertheless, some studies suggest that the prevalence of underweight tends to increase in developed countries(Reference Vanhelst, Baudelet and Fardy5–Reference Martínez-Vizcaíno, Sánchez López and Moya Martínez7). Underweight in children is also linked to many serious physical, psychological and social consequences on health from childhood to adulthood(Reference Flegal, Graubard and Williamson8,Reference Sato, Nakamura and Sasaki9) .
Monitoring the weight status in children across different countries is essential and may help identify the target population for primary prevention and health promotion policies. To date, tracking of children about their weight status (underweight, overweight and obesity) in France has been inconsistent, and data are missing since 2010(Reference Wijnhoven, van Raaij and Spinelli1,Reference Garrido-Miguel, Cavero-Redondo and Álvarez-Bueno2) .
The purpose of the current study was first to measure the prevalence of underweight, overweight and obesity in French children from 2013 to 2017 and to compare the results with findings prior to 2013.
Methods
This ancillary study used data from the French health programme ‘Diagnoform®’ (https://irfo.fr/). The principal objective of this programme was to assess the physical fitness of a large, voluntary, non-representative sample of the French population aged 5–60 years and older. This programme was divided into four categories: (i) DiagnoKid for children aged 4–10 years; (ii) DiagnoTonic for adolescents and young adults aged 10–25 years; (iii) DiagnoActif for adults aged 25–60 years; and (iv) DiagnoHealth for people aged ≥60 years. The programme was performed in large settings throughout France, such as school playgrounds or sports club gymnasiums.
All procedures were performed in accordance with the 1975 Helsinki Declaration as revised in 2008 and the European Good Clinical Practices. As the research did not involve an intervention and the data were collected retrospectively using the organisational structure of the study (Institut des Rencontres de la Forme; https://irfo.fr/), the current study was considered an epidemiological study. In this context, written informed consent was not required according to French human research regulations. All data obtained from the organiser (results of physical fitness tests and anthropometrics data) of the event were anonymous, declared and approved by the French National Commission of the Informatics Personal Data (Commission Nationale de l’Informatique et des Libertés). The aims and objectives of the Diagnoform programme were explained carefully to each child and to their parents. After this explanation, the children and parents could either accept or decline to participate in this event and to allow their data to be recorded anonymously. The data were recorded into an electronic data system by the organiser. For the current study, data analyses were performed using only children’s data.
Many schools in France were invited to participate in the study, with each school director deciding whether to participate or not. From the 356 schools invited, 309 have accepted to participate in the Diagnoform programme (i.e. 85 % of positive response). When the director accepted the invitation, all students were invited to participate. However, due to sick or absent children on the day of assessment, 11 % of students (3534) could not participate. Each year, a different group of students was measured. In addition, data were collected from fourteen of the twenty-two regions of France (i.e. 64 %). From the Diagnoform programme performed between 2010 and 2018 with an age range of 4–17 years, 32 132 (16 378 boys and 15 754 girls) volunteered to participate. Because of the small sample size of participants aged 13–17 years compared with other age–sex classes and the data obtained from 2010–2012 and 2018, we restricted the analysis to 19 916 (10 159 boys and 9757 girls) children and adolescents aged 4–12 years.
Measurements
Anthropometric measures
Body weight was measured to the nearest 0·1 kg using an electronic scale with the participant wearing light clothes and without shoes. Height was measured without shoes to the nearest 0·1 cm using a standard physician’s scale. BMI was calculated as weight/height-squared (kg/m2). Nutritional status was assessed using the IOTF scale(Reference Cole, Bellizzi and Flegal10).
Statistical analysis
Data are presented as percentages for categorical variables and as means and sd for continuous variables. The normality of distribution was checked graphically using the Shapiro–Wilk test.
Comparisons of underweight, overweight and obesity between boys and girls were assessed by the χ 2 test. Changes in underweight, overweight and obesity from 2013 to 2017 were assessed using the Cochran–Armitage trend test.
All statistical tests were performed at a two-tailed α level of 0·05. Data were analysed using the statistical software packages IBM SPSS Statistics for Windows (version 22.0; IBM SPSS), R Project for Statistical Computing (version 3.6.1) and Excel 2013 (Microsoft).
Results
The mean age of boys and girls was 8·7 ± 1·6 and 8·6 ± 1·6 years, respectively. Mean height, weight, BMI and prevalence rates of underweight, overweight and obesity by sex and age group are presented in Table 1. Overweight and obesity were significantly greater in girls compared with boys (P < 0·001) (Table 1). The prevalence of underweight was also higher in girls than boys (P < 0·01).
Table 1 Prevalence rates of underweight, overweight and obesity, and mean anthropometric characteristics with sd in French boys and girls aged 4–12 years for the period 2013–2017 (n 19 916)
Percentages are row percentages for prevalence rates by age group; percentages are column percentages for total prevalence rates by sex.
* χ 2 test was performed to assess differences in prevalence rates by sex; Student’s t test was performed to assess differences in anthropometric data by sex. Significant P values are indicated in bold.
The prevalence rates from 2013 to 2017 for boys and girls combined and by sex are presented in Table 2 and Fig. 1. No significant changes in obesity were found for boys and girls, respectively (P > 0·05) (Table 2). The proportion of overweight was lower in 2017 than in 2013 among boys and girls (P < 0·01) (Table 2). Conversely, the prevalence of underweight increased in girls and boys (from 10·0 to 20·0 %, P < 0·0001) between 2013 and 2017.
Table 2 Overall and sex-specific number, proportions (%) of children aged 4–12 years classified as underweight, healthy weight, overweight and obese in 2013 and 2017 from the Diagnoform programme
* Cochran–Armitage trend test. Significant P values are indicated in bold.
Fig. 1 Prevalence rates of (a) underweight, (b) overweight and (c) obesity among French children aged 4–12 years from 2013 to 2017. 
, total; 
, boys; 
, girls; 
, 4–6 years; 
, 7–9 years; 
, 10–12 years
Discussion
Many countries have developed public health initiatives and policies to prevent and treat unhealthy weight issues in children. Therefore, monitoring underweight, overweight and obesity in youth is essential for tracking and evaluating the effectiveness of these public health recommendations and intervention programmes. However, data on tracking in childhood are scarce, limited and missing among French children and adolescents since 2010(Reference Garrido-Miguel, Cavero-Redondo and Álvarez-Bueno2).
Using the IOTF criteria, the results of the current study suggest that the prevalence of overweight changed significantly, showing a decrease between 2013 and 2017 (17·3–13·4 %). During the same period, obesity prevalence also decreased by 38 %, from 6·1 to 3·8 %, although not significantly. These findings concur with the results of a recent meta-analysis performed from 1999 to 2016 in European children(Reference Garrido-Miguel, Cavero-Redondo and Álvarez-Bueno2). The researchers reported that in some European countries during the last two decades, the growing overweight and obesity prevalence trend had reached a plateau or sometimes showed a slight decline(Reference Garrido-Miguel, Cavero-Redondo and Álvarez-Bueno2). A similar observation was made at the international level, especially in high-income countries(11). Even though our data show encouraging results, the proportion remains high. Current national public health initiatives in children must be maintained and strengthened in the future.
Another outcome from our study is the difference in the prevalence of overweight and obesity between boys and girls. The prevalence rates of overweight and obesity were significantly higher in girls compared with boys; however, the sex differences were small (14·5 v. 16·4 % for overweight boys and girls; 5·2 v. 5·8 % for obese boys and girls). This finding is also consistent with results from previous studies(Reference Garrido-Miguel, Cavero-Redondo and Álvarez-Bueno2,11,Reference Rokholm, Baker and Sørensen12) .
Although the data on overweight and obesity prevalence from this survey are encouraging, another major concern was highlighted. Our results show an alarming progression of underweight between 2013 and 2017 among both boys and girls. The prevalence of underweight has effectively doubled in 5 years (10·0 v. 20·7 % and 10·5 v. 20·5 % for boys and girls, respectively). Previous studies have highlighted the maturing of this phenomenon and underlined the need for further attention(Reference Vanhelst, Baudelet and Fardy5,Reference Martin, Rosenberg and Pratt6,Reference Lazzeri, Rossi and Kelly13) . Since underweight is also associated with adverse health consequences (physical, psychological and social) throughout the life course, there is an urgent need to develop strategies to reduce this growing prevalence. In addition, when monitoring overweight and obesity, we recommend also systematically assessing the rate of underweight prevalence.
The current study has strengths and limitations. One of the strengths is the large sample size of children with age- and sex-specific information across France. The use of standardised procedures to assess anthropometric measures is another strength. Although the present data derive from a large sample belonging to 65 % of the French administrative regions, the current study did not use a stratified sample design. Therefore, it is not possible to assume that the studied cohort is fully representative of the child population in France. In addition, our results showing increasing underweight and decreasing overweight profiles must be used with caution because we cannot exclude whether there was a general shift in the bell curve (or spreading out) or just a difference in our sample between measurement dates (2013–2017). Indeed, due to the voluntary nature of the programme, the number of participants studied across the years differed dramatically and may affect our results. Another potential weakness is the lack of socioeconomic information, which could have impacted our findings. A socioeconomic gradient in overweight and obesity was effectively reported in most partly developed countries, with a higher prevalence of overweight and obesity being observed in more disadvantaged groups(Reference Péneau, Salanave and Maillard-Teyssier14,Reference Devaux and Sassi15) . Consequently, we recommend studies incorporating random subject selection and assessing socioeconomic status.
In summary, data from our study suggest a quite stable prevalence of obesity with a declining prevalence of overweight, despite remaining high in French children between 2013 and 2017. Our results also indicate that underweight increased significantly in both sexes. This concern becomes an important phenomenon in children and warrants careful monitoring in coming years. Based on the current results, we support the continuation of current public health policies and also encourage the development of new strategies to prevent and treat underweight issues.
Acknowledgements
Acknowledgements: The authors thank all participating youths for their collaboration in the study. Financial support: This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors. Conflict of interest: The authors declared no conflict of interest. Authorship: Each author contributed significantly to the study. J.V., J.-B.B., H.O., F.M. and T.D. designed the research; T.D. and H.O. conducted the research; J.V. and J.-B.B. analysed the data; J.-B.B. and J.V. performed statistical analyses; J.V., J.V. and D.T. wrote the article; T.D. had the primary responsibility for the final content; all authors read and approved the final manuscript. Ethics of human subject participation: The current study was conducted according to the guidelines laid down in the Declaration of Helsinki and the European Good Clinical Practices. The study was declared an epidemiological study. In this context, written informed consent was not required according to French human research regulations. Data collection was approved by the French National Commission of the Informatics Personal Data (Commission Nationale Informatique et Liberté).
