AbstractChange in eating habits in early breast cancer (EBC) patients during chemotherapy has been poorly studied in the literature. The primary aim of this study was to prospectively evaluate food preferences and weight change in EBC patients before and after adjuvant chemotherapy. From April 2014 to June 2018, 205 EBC patients underwent a dietary assessment according to the following timeline: baseline evaluation (one week before starting chemotherapy, T0); first follow-up (approximately 2–3 months after starting chemotherapy, T1); final follow-up (one week after chemotherapy end, T2). A statistically significant reduction of the following foods was reported after the start of chemotherapy: pasta or rice, bread, breadsticks/crackers, red meat, fat and lean salami, fresh and aged cheese, milk, yogurt, added sugar, soft drinks, alcoholic beverages (wine, beer, and schnapps), and condiments (oil and butter). Conversely, fruit consumption consistently increased. As a result of these changes, a Healthy Eating Index (HEI) specifically developed for this study and suggestive of a balanced diet, significantly increased. Body weight did not increase, despite reduction in physical activity. This prospective study shows that EBC patients tend to adopt “healthier dietary patterns” during adjuvant chemotherapy, leading to a non-change in weight, despite reduction in physical activity.