Thanks for the response, I'm just reading through the linked meta analysis.
It's important to remember, though, that correlations measured in twin studies, by design, only say something about the difference of both measured variable expressions, not about the variable itself. So if twin A has a BMI of 30 and twin B has a BMI of 35, that linked meta analysis says that heredity explains 75% of the difference between 30 and 35, or only 3.75 BMI points/ 10% of twin B's BMI in the given example. Even more interesting: The older the twins are, the smaller the difference gets (grep for 'decreased mean age' in the study).
It's important to remember, though, that correlations measured in twin studies, by design, only say something about the difference of both measured variable expressions, not about the variable itself. So if twin A has a BMI of 30 and twin B has a BMI of 35, that linked meta analysis says that heredity explains 75% of the difference between 30 and 35, or only 3.75 BMI points/ 10% of twin B's BMI in the given example. Even more interesting: The older the twins are, the smaller the difference gets (grep for 'decreased mean age' in the study).