This phenomenon is a normal fluctuation in body weight and is related to diet, water intake and physiological activity. If a large amount of food and water before measuring weight can lead to a significant increase in weight. Usually, after a normal diet weight can increase by about 4-6 pounds, if it is overeating, it can reach more than 8 pounds. If it is after a lot of exercise and sweating, it can lead to a significant reduction in weight. Because usually sweating can wet a set of underwear, probably can lose more than 3000ml of water in the body, so it is possible to cause weight loss of 8 pounds. However, if this is often the case, it is advisable to go to the hospital for a comprehensive examination to rule out whether the body has organic diseases, or even malignant diseases caused by.