Recent advancements in breast cancer treatment have significantly increased the number of cancer survivors worldwide. In the United States, Canada, Australia, Japan, and many European countries, the five-year survival rate of breast cancer has reached 85-90%; however, the risk of death from breast cancer is still high among high-risk women with certain comorbidities.
Epidemiological evidence indicates that obesity, metabolic syndrome, and high blood levels of glucose, insulin, and testosterone are major risk factors for breast cancer recurrence among women, even after menopause.
Nevertheless, several studies have reported that the metabolic and hormonal risk factors associated with breast cancer recurrence can be mitigated by adopting a healthy diet and lifestyle. The Mediterranean diet, which primarily includes plant-based food products, is known to reduce the risk of metabolic syndrome and improve body composition, insulin sensitivity, glucose metabolism, and blood lipid profiles.
In the current randomized controlled dietary intervention DIet and Androgen 5 (DIANA-5) trial, researchers investigate the effect of the macro-Mediterranean® diet, which involves the Mediterranean diet in combination with increased phytoestrogen intake, on breast cancer recurrence. Previous DIANA trials have reported the benefits of the macro-Mediterranean® diet in reducing insulin resistance, testosterone levels, and other factors associated with metabolic syndrome.
Study design
The current study included 1,542 breast cancer patients who underwent surgery for invasive breast cancer within the previous five years. All study participants were at an increased risk of breast cancer recurrence because of having estrogen receptor (ER)-negative breast cancer, metabolic syndrome, or high blood levels of insulin or testosterone.
Study participants were randomly assigned to the macro-Mediterranean dietary intervention group or control group. The intervention consisted of kitchen courses, monthly community meals, and dietary and physical activity recommendations.
Vegetables, fruits, nuts, olive oil, fish, whole grains, legumes, and soy products were among the recommended foods. Comparatively, refined foods, sugary foods, potatoes, red meat, processed meat, dairy products, and alcohol were not recommended. A compliance dietary index was defined by the difference between intake of recommended and non-recommended foods.
Participants from both intervention and control groups received general recommendations for cancer prevention.
Important observations
A total of 769 and 773 high-risk women with breast cancer were assigned to the intervention and control groups, respectively, and monitored for five years. In both groups, participants received a breast cancer diagnosis at an average of 1.8 years before enrollment.
In terms of pathological variables such as tumor type, size, and grade, nodal metastasis, and hormone receptor status at the time of diagnosis, participants from both groups had comparable characteristics.
The analysis of 24-hour food frequency reports at baseline revealed a similar intake of recommended foods by both groups. However, a slightly higher intake of non-recommended foods and a lower dietary index were observed in the control group.
Both groups exhibited significant improvements in anthropometric and metabolic parameters after one year. However, the changes in all parameters were comparatively higher in the intervention group.
A significantly higher reduction in body weight, body mass index (BMI), waist circumference, glucose level, triglyceride level, and metabolic syndrome parameters was observed in the intervention group as compared to the control group.
A significantly increased intake of recommended foods and reduced intake of non-recommended foods was observed in the intervention group as compared to the control group at the one-year follow-up visit. Similarly, the intervention group was associated with a significant improvement in dietary index than the control group throughout the follow-up.
Breast cancer incidence
Recurrence of breast cancer was observed in 95 and 98 participants from the intervention and control groups, respectively, over the five-year follow-up period. Additionally, both groups were associated with a similar incidence of distant metastasis. Survival rates without recurrence were also comparable between the two groups.
Study participants with a high dietary index were associated with a significantly reduced incidence of new breast cancer events than those with a low dietary index.
Significance
The consumption of the Mediterranean diet in combination with phytoestrogen does not appear to reduce the risk of breast cancer recurrence among high-risk women. However, a better prognosis of breast cancer has been observed among women with higher compliance with dietary recommendations.