Study on the Effect of Fasting on the Tolerability of Aromatase Inhibitors in Breast Cancer

Breast cancer (mammary carcinoma) is a malignant disease of the mammary gland tissue characterized by the uncontrolled proliferation of mammary gland cells. Treatment of the disease depends on numerous factors, such as the patient’s overall health, the stage of the disease, the tumor growth rate (Ki-67 index), detectable hormone receptors (HR) on the surface of the cancer cells (estrogen receptor-positive, progesterone receptor-positive), and the increased presence of HER2 receptors on the cells (HER2-positive). Cancer cells often have hormone receptors, making antihormonal therapy a core component of treatment. Aromatase inhibitors are used primarily in postmenopausal women. These drugs reduce the production of the hormone estrogen, which promotes the growth of estrogen receptor-positive breast cancer cells. The most common side effects include joint and muscle pain and fatigue.

The goal of the FREE-AI study is to investigate whether a seven-day fast with a maximum of 350 kcal per day, followed by a dietary change, can alleviate these symptoms and improve quality of life. The fasting process is monitored online via the StudyU app. In addition, the study will be used to further optimize this app.

After the fasting week, study participants will follow a plant-based, prebiotic-rich diet that incorporates intermittent fasting (the 16/8 rule), in which food intake is limited to eight hours per day. To assess the effects, study participants are asked to complete questionnaires about pain, well-being, and quality of life after the fasting phase and again three months later, following their new eating habits. The study is single-arm and open-label, meaning that both medical staff and study participants are aware of the intervention. Since there is only one study arm, the study is not randomized (random assignment to different study arms).

Eligible participants are women between the ages of 18 and 70 with hormone receptor-positive (HR+) breast cancer who have been treated with an aromatase inhibitor for at least three months and who suffer from significant pain (NRS > 4).