Menstruation, or menstruation, is a period in which you may gain weight slightly, but it does not fluctuate too much. Menstruation is due to a drop in estrogen levels in the body, the endometrium loses hormonal protection and sheds, and estrogen changes can cause fluid retention, especially sodium retention. Before menstruation, estrogen levels in the body are relatively too high, causing water and sodium retention, which in some women can lead to weight gain. After the onset of menstruation, estrogen levels drop rapidly, and weight returns to normal after water is excreted from the body. In some cases, in addition to weight gain before menstruation, headaches, breast tenderness, anxiety, and emotional instability may also occur, and serious symptoms require medical attention.