Any time that your body changes, it is trying to get ready for something. In this case, the time during a woman’s period signals that this is the time she could get pregnant. The body in turn will change to prepare for that. Also, her body is exerting energy during a woman’s period due to the increase in her basal metabolic rate. When a woman has her period, she will burn more calories. This could also make her hungry.
Also, during this time, the woman’s body may feel bloated. This may seem like she wouldn’t feel hungry but on the contrast she may not eat during the bloated time, but then may overeat after that. The woman may feel like her body was deprived of food.