Used the size guide and previous reviews and bought a large (I am 5'4 and a muscular 160 size 8ish) I probably could have used the medium.  There's no "girdle" effect but the do the trick in reducing the lower tummy line that i get on most undies and they don't roll down or cause back fat roll over top.  They look a little grannish so i'll probably reserve them for specific outfits and dresses that the tummy line is most annoying.