The use of tampons enables women to take part in most naturist activities. If you prefer to use pads instead, or if you would just feel more comfortable doing so, wearing shorts is perfectly acceptable during your period. That's the whole point though. Naturism isn't about looking at bodies - naturists are not exhibitionists. It's just about enjoying the freedom that a clothes optional atmosphere brings.
Naturism is about accepting the human body for what it is - nothing to be ashamed of.
So the men don't need to hit the gym for six months, buffing their muscles to within an inch of their lives in order to gain entry. And the women don't have to look like Baywatch babes. The media is largely responsible for promoting this idea of body perfection, but the truth is that the vast majority of people do not now, nor are they likely to ever resemble this false ideal. So for naturists there is no such thing as too fat, too thin, too short, too tall, too hairy. Nobody's going to comment on the size or shape of your breasts or critically evaluate your genitalia.