Regular exercise behaviour in youth is not related to current body mass index or body mass index at 7-year follow-up

Physical activity and dietary intake in BMI discordant identical twins

OBJECTIVE

Despite the latest discovery of obesity-associated genes, the rapid rise in global obesity suggests a major role for environmental factors. This study investigated the influence of environmental factors on physical activity and dietary intake independent of genetic effects.

METHODS

Sixteen female monozygotic twins aged 48.8 ± 9.8 years (range 37-70) with a mean BMI discordance of 3.96 ± 2.1 kg/m(2) (range 0.7-8.2) were studied. Physical activity was determined using 7-day accelerometry and dietary intake using 3-day 24-h recalls.

RESULTS

Heavier cotwins were generally less physically active (mean activity counts × 1,000 per day ± SD; 505.5 ± 155.1 vs. 579.6 ± 185.4, P = 0.047) and tended to spend 6.1 min/day less in moderate to vigorous physical activity than leaner cotwins (P = 0.09). Energy intake did not significantly differ within pairs. Total fat intake (en%; P = 0.03), specifically monounsaturated fat (P < 0.01) and polyunsaturated fat (P = 0.08), was higher in the heavier cotwins.

CONCLUSIONS

After eliminating genetic effects, higher BMI is associated with lower overall and moderate to vigorous physical activity and higher intake of total fat, although the direction of causality cannot be determined. Future identification of the environmental factors responsible for these findings might contribute to developing new strategies in managing obesity.

Regular exercise behaviour in youth is not related to current body mass index or body mass index at 7-year follow-up

Objective

This population‐based study aimed (1) to test the presence of an association between regular voluntary exercise behaviour (EB) that is performed in leisure time and body mass index (BMI) in youth and (2) to investigate the causal nature of this association using a longitudinal design in genetically informative subjects.

Design and methods

Both EB and BMI were assessed repeatedly over time in 21 458 twin individuals from the Netherlands Twin Register (47.5% male) – first by parental report (ages 7, 10 and 12) and subsequently through self‐report surveys (ages 14, 16 and 18). EB was quantified as weekly metabolic equivalent of task hours.

Results

Correlations over time were higher for BMI than for EB (r ≈ 0.70 vs. r ≈ 0.35) across 12 different follow‐up periods. Cross‐sectionally, regular involvement in EB was not associated with lower BMI in childhood and in genetically identical twin pairs discordant for EB; the exercising twin did not have a lower BMI than the non‐exercising twin. Longitudinally, linear and quadratic relationships between EB and BMI were non‐significant. Changes in EB over time did not induce opposite changes in BMI.

Conclusions

No consistent association between regular EB and BMI was observed from ages 7 to 18 years.