Breast cancer is associated with obesity and a high-calorie diet, and weight control and dietary modification are also measures that cannot be ignored to prevent breast cancer. Overweight and obese women have a significantly higher risk of developing breast cancer. In particular, the risk can increase 4.51-12.38 times in postmenopausal women. Obesity mainly in the abdomen is spindle-shaped, and obesity mainly in the hips and thighs is pear-shaped. American scholars analyzed 216 breast cancer patients and found that if the ratio of waist circumference to hip circumference is greater than 0.77, the relative risk of breast cancer is 3 times higher than normal, and if the ratio is greater than 0.8, the relative risk is 6 times higher than normal. Women’s hip and thigh fat is not easy to eliminate, but relatively less impact on breast cancer and cardiovascular disease. The opposite is true for abdominal obesity, which is easier to eliminate, but has a greater potential risk for cardiovascular disease and breast cancer. Obese women with breast cancer are more likely to develop axillary lymph node metastases. U.S. researchers examined 656 patients with recently diagnosed invasive breast cancer and found that 33% of thinner female patients had axillary lymph node metastases, compared to 66% of obese patients. Obese women with breast cancer have relatively poorer surgical outcomes and higher post-operative recurrence rates than non-obese patients. The occurrence and development of breast cancer is related to estrogen. In addition to the estrogen secreted by the ovaries, obese women also have fatty tissues that can produce considerable estrogen, and the higher the estrogen level, the more likely they are to develop breast cancer. Long-term intake of high-calorie diet leads to overweight and obesity. People who often eat fried or deep-fried food have 1.6 times more risk of breast cancer. In a controlled study conducted in Shanghai on 537 normal people and patients, it was found that the relative risk of breast cancer increased by 2.72 times for those who consumed more fat and 3.53 times for postmenopausal women who consumed more fat. People who are less active have a corresponding increase in breast cancer due to a relative excess of calories. Investigation shows that the risk of breast cancer is 1.86 times higher in women who do not exercise than in those who are physically active. The type of fat is closely related to breast cancer. Canadian scholars studied 666 female patients who were diagnosed with breast cancer and investigated their intake in the year before diagnosis. It was found that the higher the intake of saturated fatty acids from animals, the more likely lymph node metastasis occurred, while the intake of unsaturated acids from plants did not. The group with the highest intake of saturated acids had lymph node metastases in 51% of the cases. Only 41% of the group with the least amount of saturated acids had lymph node metastases. Thus, it seems that the middle-aged and elderly women should eat less animal fat and replace it with vegetable oil to prevent breast cancer and coronary heart disease.