Breast cancer is the most common cancer in women, both in developed and less developed countries. The incidence of breast cancer is on the rise worldwide, especially postmenopausal breast cancer and estrogen receptor-positive breast cancer are the most significant. So can diet and lifestyle changes prevent breast cancer? What is the evidence? Key points ● Overweight, obesity and weight gain are all associated with postmenopausal breast cancer, while alcohol consumption and lack of exercise can increase the risk of breast cancer before and after menopause. ● Rapid height growth or exposure to tobacco and alcohol during menarche and first pregnancy may increase the risk of breast cancer, as rapidly developing breasts are particularly sensitive to carcinogenic factors. ● Maintaining a healthy diet, while not specific for reducing breast cancer risk, is still important for women because it reduces other common diseases such as cardiovascular disease, diabetes and dementia. ● Overweight, alcohol and lack of exercise increase the risk of cancer in women with a family history of the disease, but their specific association with carriers of BRCA1 and BRCA2 gene mutations needs further study. Breast cancer is the most common cancer in women in both developed and less developed countries. The incidence of breast cancer is on the rise worldwide, particularly in postmenopausal breast cancer and estrogen receptor-positive lesions. Cancer Prevention Guidelines Cancer prevention guidelines from the World Cancer Research Fund (WCRF) and the American Cancer Society (ACS) recommend maintaining a healthy weight, at least 150 minutes of moderate intensity exercise per week, limiting alcohol intake, and a plant-based diet. Observed data suggest that lifelong adherence to guidelines for physical activity and alcohol restriction reduces the risk of premenopausal and postmenopausal breast cancer. Lifetime weight control may prevent the development of postmenopausal breast cancer. Maintaining a healthy diet, while not having a specific role in reducing the risk of breast cancer, is still important for women because it reduces other common diseases such as cardiovascular disease, diabetes and dementia. Accumulating data now show that smoking during adolescence or early adulthood can increase the risk of developing breast cancer later in life. Although the impact of lifestyle factors on BRCA mutation carriers is unclear, it can influence the risk of breast cancer in women with a high family history of risk factors and in women with typical risk factors. Recent expert reports estimate that successful lifestyle changes can prevent 25-30% of breast cancer cases. To achieve these preventive effects, we should implement targeted prevention programs for women at risk and population-based breast cancer screening for the general population in childhood, adolescence and early adulthood, when rapid breast development is particularly sensitive to carcinogenic factors. BRCA1 and BRCA2 carriers: lifestyle changes to reduce risk Over the past century, there has been an increase in breast cancer incidence in both the general population and in those at high risk for mutations in the BRCA1 and BRCA2 breast cancer susceptibility genes. A published data set from Iceland shows that the cumulative incidence of breast cancer (before age 70) increased fourfold between 1920 and 2000 in BRCA2 carriers (18.6% to 71.9%) and in the general population (1.8% to 7.5%). A series of cohort studies has shown a significant increase in the epistasis of BRCA gene mutations over the years, a phenomenon thought to be a reflection of increased reproductive and lifestyle risk factors, although its exact cause is not known. High-quality large genome-wide association studies have established that genetic alterations at this locus affect BRCA epistasis. Comparatively, studies on risk factors are still mainly small case-control studies that retrospectively collect information on lifestyle-related risk factors that are inevitably subject to clinically based environmental bias and survival bias, and the findings have not been replicated and validated in independent settings. These studies have generated some evidence to be further established that among BRCA1 and BRCA2 carriers, cancer risk is increased in overweight and smoking populations and decreased in physically active individuals (occurring especially in adolescence and early adulthood), with a consistent negative effect of alcohol effects. The shortcomings of these studies have been recognized, and large prospective studies are imperative. Recent data from a prospective cohort study in New York showed that adherence to cancer prevention guidelines, maintaining a healthy weight, reducing alcohol and increasing physical activity reduced breast cancer mortality by 61% in BRCA1 and BRCA2 carriers (hazard ratio 0.39; 95% CI, 0.16 to 0.97) Preventing breast cancer with lifelong lifestyle changes In a Western cohort study , 75-80% of breast cancers occur after menopause and these cases can be well prevented, compared to 20-25% of premenopausal breast cancers, and prevention in these patients must begin early in life. The risk of breast cancer can accumulate during childhood, adolescence, and especially during the period of menarche and first pregnancy, when breast cells are undifferentiated and sensitive to carcinogenic factors (Table 2). Excessive growth in childhood and excessive alcohol and tobacco consumption in early adulthood increase the risk of cancer, whereas soy intake during this period may reduce the risk of development. Weight gain during the premenopausal and postmenopausal periods increases the risk of postmenopausal (but not premenopausal) breast cancer. Therefore, preventive interventions for breast cancer should focus on preventing premenopausal weight gain. Obesity in childhood or early adulthood does not increase the risk of breast cancer and may sometimes place this group of women at low risk. This paradox of weight on breast cancer risk is unclear, but it likely reflects the fact that young overweight women do not gain significant weight in adulthood, and it is weight gain in adulthood that places women at high risk for cancer. In addition, serum progesterone concentrations tend to be lower in young overweight women.