Familial resemblance of body weight and weight/height in 374 homes with adopted children.

Body weight and weight/height were measured in 535 children adopted at the median age of 3 months, and in 250 natural children in French-Canadian origin living in 374 Montreal homes, to determine whether the shared environment contributed to the familial resemblance of weight in children aged one to 21. The mid-parent vs natural children's correlation ( r2 X 100) was 9.55% for body weight and 6.60% for W/H (p less than 0.01), whereas the mid-parent vs adopted children's correlation was 0.00% for both characteristics. The sib-sib correlation in 80 homes with greater than 1 natural child was 15.2% for weight and 13.48% for W/H (p less than 0.001), whereas in 138 homes with greater than 1 adopted child, the adoptee-adoptee correlations were, respectively, 0.00% and 0.07%. It is concluded that heredity explains most of the familial aggregation of patterns of weight and weight/height in children. This conclusion does not necessarily apply to obesity, since weight indices in children do not accurately reflect excess fat tissue, and half of the adoptees were adopted after the age of three months.