There are three aspects of ritual of karva chauth . One is fasting the whole day without water, the other is ritual of seeing the moon through a sieve, and other is looking at your husband through a sieve .It is known that moon can cause tidal waves in ocean and since we all carry a part of ocean of same salinity with us , it can affect our biological self. The aim of the fast is to produce dehydration so that the affect of full moon ( gibbus) is not as strong on our body. Looking at the moon through a sieve is symbolic of the same. To Reduce the harmful affects of moon on your body. Along with autophagy the dehydration produced will help the body be disease free . Similarly the custom of looking a male through a sieve also signifies something. It is known that Men get violent during full moon. That the woman is fasting for her husband’s long life will pacify the most disturbed husband.Thus karva chauth is a fast to protect women from harmful moon and dangerous husbands 😄