Up to this point we have been discussing theoretical and known genetic mechanisms that might explain why there is so much obesity around. There is also strong epidemiological evidence. For example, the more overweight the parents, the more likely the child wil be overweight and that the overweight will persist into adulthood. If only one parent is overweight, the risk for the child is increased 6.8-fold; if both parents are overweight, the risk is 8.4-fold. One might argue that such data do not prove genetic causes, since environmental factors could also be to blame. I agree. But, if we look at data from twin studies, rates for overweight in identical twins, even raised apart show nearly 100% concordance- if one twin is overweight, the other is almost certain to be overweight also. The opposite is also true- if one of an identical twin pair is slender, the other twin is almost certain to be slender as well. These relationships do not hold for fraternal (nonidentical) twins. Clearly, genetic factors contribute to obesity and are powerful forces with which to contend. Next entry we will begin a discussion of non-genetic causes, those we are most able to modify.
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