Women on average have around five percent more body fat than men. Women have more enzymes for storing fat and far fewer for buring fat than men. Furthermore estrogen both activates and multiplies fat storing enzymes.
Owing to their menstrual cycle women often retain water leading to their weight fluctuating day to day. This retention and changes in hydration levels can make measuring body fat using the BIA method quite difficult.
If women regularly monitor body fat they should establish a baseline for a month and compare this to make sure they compare like with like. Monitoring this way will enable them to anticipate monthly trends.