This study aimed to determine if dietary modifications using a nutritional regimen could prevent or reduce the incidence of cancer therapy-induced diarrhea in patients with metastatic colorectal cancer and to evaluate the relationship of Vitamin D blood levels with diarrhea severity. Patients with metastatic colorectal cancer were enrolled. A Mediterranean diet, containing some special limitations aiming to reduce the risk of diarrhea, was administered before and during the entire chemotherapy program. Enrolled patients numbering 60/137 (44%) had diarrhea during chemotherapy. Adherence to the diet was high in 36 (26.3%) patients, medium in 94 (68.6%), and low in 7 (5.1%). Mean adherence to the diet was significantly lower in patients who experienced diarrhea with maximum grade 2−3 compared to those who had no diarrhea or grade 1 diarrhea (score = 5.4 ± 1.9 vs. 7.1 ± 1.5, p < 0.001). Patients with higher adherence to the diet had a lower risk of grade 2−3 diarrhea (odds ratio: 0.5 (95% CI: 0.3−0.7, p < 0.001)). In addition, patients who completed a higher number of chemotherapy cycles had an increased risk of grade 2−3 diarrhea (odds ratio: 1.2 (95% CI: 1.0−1.5, p = 0.02)). Of note, a lower level of Vitamin D correlated with an increased risk of G2-G3 diarrhea (p = 0.03). A diet based on vegetables with a controlled fiber content, Mediterranean Modified Healthy Diet (MMHD), is useful to control the incidence of cancer therapy-induced diarrhea.
Keywords: Vitamin D; cancer therapy-induced diarrhea; colorectal cancer; diet.