The reason for low menstrual flow during fat loss is that irrational dieting leads to nutritional deficiencies, the ovaries lose their normal function, and endocrine disorders caused by taking weight loss medications cannot be ruled out, so it is necessary to consult a doctor in time to make a clear diagnosis. 1. irrational dieting leads to nutritional deficiencies and loss of normal ovarian function, generally through dieting to lose weight women, nutritional intake is far from adequate, irrational eating habits and dietary patterns, resulting in insufficient nutrients supplied to the ovaries, and can not allow the ovaries to normal secretion of estrogen and progesterone, the menstrual cycle is out of whack, and even amenorrhea and other situations occur. 2. Taking weight-loss drugs may lead to endocrine disorders, causing hormone secretion levels to be disorganized, and estrogen and progesterone secretion to lose its rhythmicity, which may result in low menstrual flow. Weight loss requires a healthy diet, should not be excessive dieting, should be appropriate exercise to maintain good health.