[Influence of body weight on the prognosis of breast cancer survivors; nutritional approach after diagnosis].

Obesity combined with breast cancer is a public health problem, given the high incidence and prevalence of both diseases. The aim of this review is to determine the current status of research on the relationship between the body weight of breast cancer patients and their prognosis. Overweight and obesity at the time of diagnosis are associated with a worse prognosis in breast cancer survivors. Observational studies show that breast cancer mortality is 33% higher in obese than in non-obese survivors. Furthermore, weight gain after diagnosis is common in these patients and is even greater in those receiving chemotherapy. Weight gains of 2-8 kg are observed in 68% of patients 3 years after diagnosis. Each 5 kg increase in body weight is associated with a 13% increase in breast cancer specific mortality. The mechanisms that cause this weight gain are not totally known. A higher weight gain is also associated with higher the risk of co-morbid cardiometabolic diseases, which worsen the quality of life and shorten overall survival. On the other hand, excess adipose tissue is an indirect promoter of tumor cell proliferation and releases circulating estrogens. Hence, preventing excess weight is important in these patients. An important limitation is the small number of randomised controlled trials investigating the type of diet that could be recommended specifically to breast cancer survivors. The evidence from current studies suggests that a healthy diet, low in fat and simple sugars and with a high proportion of fruit, vegetables and wholegrain products, has the potential to reduce morbidity and the risk of recurrence significantly, thus improving prognosis and quality of life in the long term.