Now of course you do want an answer to that question, though. How much does human hair really weigh?

Really, if you're going to start worrying about how much your hair weighs, what if you eat a quarter pounder burger? That is a quarter pound of "meat" that is sitting in your stomach! Shouldn't that count? Shouldn't you fast for three days straight before you weigh yourself, to see what your "body" actually weighs?
The problem here is that starving yourself then causes other weight issues. It's not worth it to know what your body weighs when it has no food, no water, and nothing else inside it. If you're trying to maintain a healthy weight, that means HEALTHY. That means you have adequate food and water inside it, and adequate hair on the outside :)
I realize that people want to be "less weight" and that they start to go a little batty when they hit a plateau. They want to do something - anything - to get that number to lower. The key here is to remember that it is NOT about a raw number. If for example you were 130 pounds and had the lean, well defined (but heavy) muscles of a ballet dancer, you would look FABULOUS. You would be sculpted and fine looking. If on the other hand you were 130 pounds and it was all jiggly flab, you would look less great. It's not just about the numeric pounds on you. It is about how healthy you are, and how those pounds are distributed.
So keep in mind, when you weigh yourself, that you might be the same "weight" - but that your fat could be converting into muscle. That is part of how becoming healthy works. It's a number of different changes that are happening in your body. Invest in a scale that can measure your fat percentage and water percentage. You might be amazed at how you are becoming more healthy every day, even though you temporarily are staying a static weight.

Lisa Shea's Library of Low Carb Books