Women have a important biological rhythm they experience every month that affects productivity, weight, sex drive, energy, and mood. It is essential to be aware of and take care of this rhythm, but it has been widely ignored by medical, nutrition and fitness research. So as women, we diet, we deprive, and we cram as much as possible into our day, striving to accomplish impossible to-do lists, and scheduling our lives based on a 24-hour time cycle, ignoring the intuitive time our bodies naturally keep: a monthly cycle with four hormonal phases that offer incredible advantages.