Abstract
Obesity is considered to be caused by an over consumption of energy rich foods and reduced energy expenditure or a combination. Low physical activity alone has not been proven to cause obesity. Recently, however, a large and well-designed longitudinal physical activity study in US girls followed up for 9–10 was published. A cohort of 1152 black and 1135 white girls were prospectively followed from ages 9 or 10 to 18 or 19 years with a validated physical activity method at multiple times including overall activity. BMI differences at ages 18 or 19 years between active and non-active girls were about 3 kg/m2 and similar differences were found in the sum of skin fold thickness without any significant differences in energy intake. (Sue Kimm et al. The Lancet. 2005; 366: 301–307).
Thus, it seems that physical inactivity plays a substantial part in weight-gain during adolescence even though BMI may overestimate a fat increase, since BMI also includes lean body mass and bone, body compartments which increase among adolescents. However, the difference in skinfold measurements between the groups indicate an increase in body fat among those who are physically inactive.