Your pituitary gland secrets a hormone(TSH=thyroid stimulating hormone) that tells your thyroid when to secrete its hormone.
(Your thyroid maintains you metabolism and body temperature)

If you TSH levels are low, it would actually mean your metabolism is higher.

BECAUSE if your pituitary gland sees your thyroid isnt doing its job, then it produces HIGHER levels of TSH to tell the thyroid to pick up the slack.
(and vice versa)

I will not be drawn in to medical arguments on this forum (or turn in my medical license).

Extensive links from the National Institutes of Health on thyroid disease here:
http://www.nlm.nih.gov/medlineplus/t...ases.html#cat5

Sskar's right, we're fat chicks, not doctors. If you think you have a thyroid issue or if you think it's not correctly regulated, talk to your doctor.