Sefer Ha’mitzvos Ha’Katzar (The concise book of mitzvos) By the Chofetz Chaim
This book lists the Torah mitzvos that can be observed today
Second Section – the Negative Commandments
152. It is a negative commandment “do not eat or drink on Yom Kippur”
As it states in Vayikra (Leviticus) 23:29, “any soul that does not have affliction will be cut off.” Anyone who eats on Yom Kippur the size of a large date, which is less than the size of an egg, of food fit for human consumption is spiritually excommunicated. If it was done in error, he is required to bring a sin offering. All foods eaten combine to add up to this minimum quantity. A person who drinks a liquid fit for human consumption that is more than a cheekful, which is less than a quarter of the size called a “log”, is spiritually excommunicated. All liquids drunk combine to add up to this minimum quantity. Less than the amounts mentioned above is forbidden from Torah law but a person is not spiritually excommunicated. He receives lashes of disobedience. According to the laws of the Sages, the following are also forbidden are Yom Kippur: washing, anointing, wearing leather shoes, and marital relations. If a person transgresses these, he receives lashes of disobedience.
This applies in all places and at all times, for men and for women.