During the six-month-long hospital stay, breast cancer patients often lack effective physical activity due to the need for treatment and the care of their families, resulting in frequent bed rest and therefore a significant weight gain compared to the pre-treatment period. Some patients also experience significant weight loss as a result of heavy adverse effects during treatment. Both significant weight gain and weight loss are closely related to the prognosis of breast cancer and should be taken seriously. Why do we need to control our weight? It has been reported in the literature that breast cancer patients with ≥5.0% weight gain have a 12% increased risk of all-cause mortality and those with ≥10.0% weight gain have a 23% increased risk of all-cause mortality compared to those who maintain the same weight (<±5%). Reducing body weight by an average of 0.45 kg (6 lb in the original text) through a low-fat diet significantly reduced the risk of recurrence in postmenopausal breast cancer patients. Similarly, compared to those with no change in weight, the risk of recurrence increased by 40% if the body mass index increased by 0.5-2.0 kg/m2 after breast cancer diagnosis, and by 53% if it increased by 2.0 kg/m2 or more. Breast cancer patients should reach a healthy weight range of 18.5-23.9 kg/m2 BMI as soon as possible after treatment.(BMI = kilograms of body weight divided by the square of height) Why should I be physically active? Physical activity after breast cancer diagnosis is associated with reduced breast cancer recurrence, breast cancer mortality and overall morbidity and mortality; in addition, physical activity is associated with improved physical fitness, self-reported health status and reduced lymphedema and complications; and physical activity also relieves tension and depression and improves self-perception; performing moderate intensity aerobic and endurance training increases bone density, improves cardiorespiratory fitness, muscle strength, and increase lean body mass. Specific recommendations are as follows: 1. Avoid a sedentary lifestyle after diagnosis and resume daily physical activity as soon as possible before diagnosis. 2. For adult patients aged 18-64, adhere to at least 150 min of moderate-intensity exercise (roughly 30 min five times per week) or 75 min of high-intensity aerobic exercise per week, and strength training (large muscle group resistance exercise) at least twice per week. Exercise in groups of 10 min, preferably every day to ensure the exercise. 3, older patients > 65 years old should try to follow the above recommendations for exercise, if combined with chronic diseases that limit mobility, then according to the guidance of the physician to adjust the exercise time and exercise intensity, but should avoid prolonged inactive state.