Since a man's and woman's heel are shaped differently, you may not get a good fit. Although individual brands may run small or large, the general rule of thumb is womens' shoes are 2 sizes smaller than mens'.
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Ive been experimenting with and researching supplements for years, but I have yet to find a weight loss supplement that actually works. There are a few that appear to be mildly effective. This includes Caffeine, Green Tea and Glucomannan (a fiber that can reduce appetite). However, the results are usually weak and inconsistent and certainly nothing to get excited about.
At the end of the day, the only thing that is really proven to help you lose weight is changing your diet.