Physical inactivity and obesity: a vicious circle

Abstract

Objective: Physical activity (PA) begins to decline in adolescence with a concomitant increase in weight. We hypothesized that a vicious circle may arise between decreasing PA and weight gain from adolescence to early adulthood.

Methods and procedures: PA and self-perceived physical fitness assessed in adolescents (16-18 years of age) were used to predict the development of obesity (BMI > or =30 kg/m(2)) and abdominal obesity (waist >/=88 cm in females and > or =102 cm in males) at age 25 in 4,240 twin individuals (90% of twins born in Finland, 1975-1979). Ten 25-year-old monozygotic (MZ) twin pairs who were discordant for obesity (with a 16 kg weight difference) were then carefully evaluated for current PA (using a triaxial accelerometer), total energy expenditure (TEE, assessed by means of the doubly labeled water (DLW) method), and basal metabolic rate (BMR, assessed by indirect calorimetry).

Results: Physical inactivity in adolescence strongly predicted the risk for obesity (odds ratio (OR) 3.9, 95% confidence interval (CI) 1.4-10.9) and abdominal obesity (4.8, 1.9-12.0) at age 25, even after adjusting for baseline and current BMI. Poor physical fitness in adolescence also increased the risk for overall obesity (5.1, 2.0-12.7) and abdominal obesity (3.2, 1.5-6.7) in adulthood. Physical inactivity was both causative and secondary to the development of obesity discordance in the MZ pairs. TEE did not differ between the MZ co-twins. PA was lower whereas BMR was higher in the obese co-twins.

Discussion: Physical inactivity in adolescence strongly and independently predicts total (and especially) abdominal obesity in young adulthood, favoring the development of a self-perpetuating vicious circle of obesity and physical inactivity. Physical activity should therefore be seriously recommended for obesity prevention in the young.

Figure 1

A. The frequency of leisure-time physical activity (mean (SE) days per year from prospective questionnaires) and B. mean (SE) BMI (from health registries) from 16 to 25 years in 10 weight-discordant and 9 weight-concordant MZ twin pairs. *p<0.05, ***p<0.001

Figure 2

Past and present leisure-time physical activity (LTPA) (from the Kriska Interview (25)) in 10 weight-discordant and 9 weight-concordant MZ twin pairs. Data are mean (SE).

Figure 3

Self-perceive physical fitness from 16 to 25 years in 10 weight-discordant and 9 weight-concordant twin pairs.

Figure 4

Daily mean (SE) accelerometer counts from the one-week measuring period in five weight-discordant MZ twin pairs.

Figure 5

Accelerometer measurements during three days in a male MZ obesity-discordant pair illustrating low overall and lack of high-intensity exercise in the obese co-twin.