I just read this interesting article about the effects of weight on performance in sports like running and biking:

The problem is that everyone has a point at which further weight loss actually makes their performance worse, said Dr. Mark Tarnopolsky, a muscle metabolism researcher and physiologist at McMaster University in Ontario. Dr. Tarnopolsky, who is a nationally ranked athlete in winter triathlons, adventure racing and ski orienteering, said that people vary so much that there is no formula to figure out the perfect weight…“Your body will tell you” your perfect weight, he said, and when you are there, “you will feel fast, race fast.”

Interesting.  It seems that thinner is better to a point, but if you get too thin things start breaking down.   I think I have a long time before I have to worry about getting too thin.

Link to Source (NY Times)