OBESITY IN CHILDREN AND ADOLESCENTS

M.F. Rolland-Cacher

ISTNA-CNAM INSERM Group, Paris, France

Obesity is usually defined using skinfold measurements and/or the weight/height2 body mass index (BMI). In adults BMI cut-off values are defined on the basis of mortality risk. A classification for BMI has been recommended by WHO. To date, there has not been the same level of agreement for defining obesity in children. The main difference between childhood and adulthood is that children grow in size, so that anthropometric cut-offs for fatness need to be adjusted for age. Obesity can be defined on the basis of BMI growth charts, choosing the highest centiles as cut-off values. As most studies use different methods, it is not possible to provide general statistics on the prevalence of childhood obesity. However, measurements recorded at different period provide information on time trends of childhood obesity. All studies report an important increase of childhood obesity. For example in France, the prevalence of obesity increased from 3% to 10% in 10 year-old-children born in 1955 and 1985 respectively.

Childhood obesity presents different aspects.

– during childhood, most fat children do not stay fat, and this is particularly true in early childhood. The low tracking of BMI between early and late childhood can be clearly understood following the development of individual BMI curves. The age at the nadir of the curve named "adiposity rebound" predicts subsequent development: the earlier the age at adiposity rebound, the higher the risk of later obesity.

– childhood obesity is associated with abnormal growth pattern. Fat children have an early maturation, accelerated growth, early adiposity rebound, android body fat distribution, and girls have early menarche.

The early adiposity rebound recorded in most obese children suggest that determinants of the development of obesity have operated early in life. The infant diet is characterized by a low fat-high protein content which is the opposite composition of human milk. Hypothesis have been proposed to account for the association between nutrient balance and fatness development. By contrast with the high level of growth hormone and low levels of IGF1 reported in protein-energy deficiency, growth hormone levels of IGF-1 reported in protein-energy deficiency, growth hormone level is reduced and IGF 1 are elevated in obese children. This alteration of the hormonal status could be the consequence of high protein intake in the obese and could account for their accelerated growth.

Sedentary lifestyle may also play a role on the abnormal development of obese children, by promoting a positive energy balance, and also by altering hormonal status.

Evidence suggest that obesity during childhood may have long-lasting adverse effects on health, even when body weight return to normal after adolescence. Childhood obesity is then a major health problem.

Studies on the origin of the abnormal pattern of growth characteristic of the obese children may provide useful information to understand the origin of obesity and associated risk factors.