OBJECTIVE:

Application of a new investigative strategy to assess genetic and environmental influences on relative body weight.

DESIGN:

Covariance structure analysis of body mass index (BMI) using genetically informative samples.

SUBJECTS:

One-hundred and fourteen monozygotic (MZ) twin pairs (age 5.04-22.93 y), 81 dizygotic (DZ) twin pairs (age 6.05-16.52 y), and 98 virtual twin (VT) pairs, ie same-age unrelated siblings (3.68-54.75 y).

MEASUREMENTS:

Height, weight, BMI variously obtained by direct measurement and self-report.

RESULTS:

In contrast with most previous studies, significant common environmental influence on BMI was observed.

CONCLUSION:

Much past research may have underestimated common environmental effects on BMI because the designs lacked the power or ability to detect them.