It’s definitely true for most women, although the severity varies a lot between individuals. The menstrual cycle is regulated by a number of glands, which produce different hormones during different stages of the cycle. These hormone fluctuations are responsible for a number of side effects, including a build-up of fluid in the extremities (hands and feet) and the breasts. If fluid retention is a problem, it usually occurs during the last week of the cycle, and is one of the many well-known symptoms of pre-menstrual syndrome (PMS).
The difference this makes to a woman’s weight is usually no more than about half a kilogram, but it can be more in susceptible individuals. Once a period begins, the fluid usually dissipates within a few days.
Whilst it’s possible to treat this with diuretics, this is only usually recommended in extreme cases, where the symptoms cause major discomfort. The best approach for most women is to keep up their water consumption, watch their salt intake and just wait for it to pass. Some like to use dandelion tea, and some green vegies, such as celery, asparagus and fennel are also reputed to help.
Whilst it is annoying, it’s only a temporary effect and won’t affect weight loss in the long term. Being aware of the timing of your cycle can be helpful though, so that you don’t freak out over a minor weight gain at “that time”. This is especially important if PMS tends you make you more emotional and maybe even just a little crazy...
Just continue to eat and exercise as normal, and try not to worry about some minor fluctuations in scale weight.