Background: Fasting during the holy month of Ramadan is a religious ritual practiced by the majority of Muslims around the globe. This daytime fasting is short-term or intermittent fasting, which may be associated with valuable health benefits, particularly in cancer patients.Methods: A prospective cohort study of pre-and post-fasting evaluation of 37 colorectal cancer (CRC) patients was conducted at King Abdulaziz Medical City (KAMC) and King Abdullah Specialized Children's Hospital (KASCH)-oncology outpatient clinics. The study aimed to assess the impact of fasting during the holy month of Ramadan on the tolerability of chemotherapy side effects and to assess changes in the levels of carcinoembryonic antigen (CEA) and lactate dehydrogenase (LDH) tumor biomarkers, which are primarily associated with certain types of carcinomas, including CRC.Results: A total of 33 patients (89.2%) had fasted at least part of the month of Ramadan. Twenty-seven patients (73%) reported "Serenity" after fasting during Ramadan with improved tolerability of chemotherapy side effects. However, the results did not reveal any significant difference in the measured laboratory variables between pre-fasting values and by the end of the 30 days of Ramadan. Although statistically insignificant, the levels of CEA and LDH were reduced in 46.9% and 55.6% of patients, respectively. The mean level of CEA in the fasting group was substantially reduced by more than 40%, attributed to the highly significant decline of CEA levels in three patients (p=0.0283). Moreover, there were no significant differences between pre-and post-fasting blood creatinine levels or estimated glomerular filtration rates, ruling out any possible adverse effects of fasting on renal function. Conclusion:The current study confirms the safety and tolerability of intermittent fasting in CRC patients actively receiving chemotherapy, which is consistent with several reports. Nonetheless, the results did not reveal a significant decrease in CEA and LDH tumor biomarkers.

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Background Fasting during the holy month of Ramadan is a religious ritual practiced by the majority of Muslims around the globe. This daytime fasting is short-term or intermittent fasting, which may be associated with valuable health benefits, particularly in cancer patients. Methods A prospective cohort study of pre- and post-evaluation of 37 colorectal cancer (CRC) patients was conducted in the oncology outpatient clinics to assess the impact of fasting during Ramadan on the tolerability of chemotherapy side effects and to assess changes in the levels of carcinoembryonic antigen (CEA) and lactate dehydrogenase (LDH) tumor biomarkers. Result The vast majority of CRC patients (89.2%) had fasted at least part of the month of Ramadan. Most (73%) reported “Serenity” after fasting during Ramadan with improved tolerability of chemotherapy side effects. The results did not reveal any significant difference in the measured laboratory variables between pre-fasting values and by the end of the 30 days of Ramadan. Although statistically insignificant, the levels of CEA and LDH were reduced in 46.9% and 55.6% of CRC patients, respectively. The mean level of CEA in the fasting group was substantially reduced by more than 40%, attributed to the highly significant decline of CEA levels in three patients only (p=0.0283). Conclusion The current study confirms the safety and tolerability of intermittent fasting in CRC patients actively receiving chemotherapy, which is consistent with several reports. Nonetheless, the results did not reveal a significant decrease in CEA and LDH tumor biomarkers.