Why has my weight increased on the third day of my period?
Nov 11, 2025
Source: Cainiu Health
Dr. Zhang Lu
Introduction
In general, weight gain on the third day of menstruation may be caused by factors such as fluid and sodium retention during the menstrual period, changes in dietary patterns, premenstrual syndrome, hypothyroidism, or polycystic ovary syndrome. It is recommended to seek medical attention promptly, identify the underlying cause, and receive symptomatic treatment under a doctor's guidance. During menstruation, it is important to maintain a relaxed mindset and avoid anxiety over short-term weight fluctuations.
Generally, weight gain on the third day of menstruation may be caused by factors such as menstrual water and sodium retention, changes in diet during menstruation, premenstrual syndrome (PMS), hypothyroidism, or polycystic ovary syndrome (PCOS). It is recommended to seek medical advice promptly, identify the underlying cause, and receive symptomatic treatment under a doctor's guidance. Detailed analysis is as follows:
1. Menstrual water and sodium retention: Hormonal fluctuations during menstruation—particularly increased estrogen—can cause the body to retain water and sodium ions, leading to tissue edema and apparent weight gain. No special treatment is required. Reducing salt intake, drinking more warm water to promote metabolism, avoiding prolonged sitting, and engaging in light walking can help. Weight typically returns to normal after the menstrual period ends.
2. Changes in diet during menstruation: Consuming excessive high-sugar, high-fat, or high-salt foods during menstruation, or increased appetite leading to caloric surplus, may result in fat accumulation and weight gain. Adjusting the diet by consuming more low-calorie, high-fiber foods such as vegetables, whole grains, and lean meats, while controlling portion sizes and avoiding binge eating, can help manage this.
3. Premenstrual syndrome (PMS): Related to hormonal changes during the menstrual cycle, PMS may present not only with weight gain but also symptoms such as breast tenderness and mood swings. Patients may follow medical advice to use medications such as vitamin B6 tablets, spironolactone tablets, or fluoxetine capsules to alleviate symptoms.
4. Hypothyroidism: Insufficient thyroid hormone secretion slows down metabolism, making the body prone to fluid and fat accumulation. This may worsen weight gain during menstruation and is often accompanied by symptoms such as fatigue and cold intolerance. Patients should follow medical instructions to take medications such as levothyroxine sodium tablets, thyroid tablets, or Yikang capsules for treatment.
5. Polycystic ovary syndrome (PCOS): Hormonal imbalances in PCOS lead to metabolic abnormalities, increasing the likelihood of water and sodium retention and fat accumulation. Weight gain during menstruation is often significant and may be accompanied by irregular periods, hirsutism, and other symptoms. Patients may follow medical advice to use medications such as ethinylestradiol/cyproterone acetate tablets, drospirenone-ethinyl estradiol tablets, or metformin hydrochloride tablets to regulate hormones and metabolism.
During menstruation, it is important to maintain a relaxed mindset and avoid anxiety over short-term weight fluctuations. Wearing loose, comfortable clothing reduces physical constriction. Attention should also be paid to personal hygiene, including frequent changing of sanitary products, while avoiding intense exercise and excessive fatigue.
