From what I have read, the difference between a super fast BMR and a super slow one is 100-200 calories. These sites for things like hypo/hyperthyroidism and PCOS will tell you these condishuns can only account for 5-10lb if left completely unchecked and with no dietary changes. It's nothing at the best of times. When you consider that the majority of a BMR will come from body tasks that are all but uniform for every person (brain function, heart beat, diaphragm, digestion, cell turnover, etc), it is pretty easy to see how the remainder that could be affected by a condishun is tiny.