Narrator: This is Science Today. Why is it that some people can eat what they want, not exercise and yet still maintain good cholesterol levels? According to a study led by the Lawrence Berkeley National Laboratory, it's all in the genes. Paul Williams, a researcher in the Lab's Life Sciences Division, says they studied 28 pairs of identical twins – one twin was a marathon runner, the other was much less active.

Williams: We were interested in finding out how identical twins would respond to high fat and low fat diets. This is in part motivated because some initial observation of ours suggested that the exercisers might have some protection from eating high fat diets.

Narrator: But their study found this was not the case – if one twin ate a high fat diet without increasing his bad, or LDL cholesterol, then so could his twin.

Williams: I think this starts to suggest that a great deal of the regulation of the bad cholesterol is through genes. We tend to tell everybody to follow a certain diet and there's a pragmatic part about it, but then people have to realize that there's a lot affecting how successful it's going to be in lowering their cholesterol.

Narrator: For Science Today, I'm Larissa Branin.