Fasting, Intermittent

Although standard neoadjuvant chemoradiotherapy (nCRT) for locally advanced rectal cancer (LARC) effectively reduces local recurrence, radiotherapy-related toxicities and surgical complications severely impair patients' quality of life, making a radiotherapy-free strategy urgently needed. However, chemotherapy alone yields a pathological complete response (pCR) rate of only 6.6%-15%, which is far from satisfactory. The pMMR/MSS subtype, accounting for 90% of rectal cancers, is "immune-cold" and shows almost no response to PD-1 monotherapy; nonetheless, chemotherapy can reshape the tumor immune microenvironment, and multiple studies have demonstrated that combining chemotherapy with PD-1 inhibitors (without radiotherapy) can elevate pCR rates to 26.8%-42.9%, yet further improvement remains desirable. A recent mechanistic study published in Cell Metabolism (2026) revealed that a single 16-hour fasting episode before treatment promotes isoleucine accumulation in the tumor microenvironment, which enhances CD8+T-cell cytotoxic function and reduces exhaustion through acetyl-CoA metabolism and epigenetic reprogramming, thereby significantly sensitizing PD-1 inhibitors-and this intervention is non-invasive, low-cost, and easily adoptable by patients. Based on the above evidence, we hypothesize that the neoadjuvant triple-combination regimen of "16-hour fasting + chemotherapy + PD-1 inhibitor" (radiotherapy-free) in pMMR/MSS locally advanced mid-to-low rectal cancer may further increase pCR rates and tumor regression, offering a novel, highly effective, and low-toxicity therapeutic option for LARC patients.

Cancer-related fatigue affects at least 30-90% of patients with cancer, depending on the type of cancer and their treatment(s) (e.g., chemotherapy, radiation). It is not relieved by sleep or rest, and it sometimes can persist for years after a person's cancer was treated. The fatigue can be so bad that people cannot return to work, hobbies, family roles, or other daily activities, thereby greatly reducing quality of life. The causes of this fatigue are unknown, and we currently do not have anything that can reliably prevent or cure the fatigue. However, there are recent data suggesting that circadian rhythm, or a person's internal body clock, may be disrupted by the cancer experience and contribute to fatigue. Food intake is an external cue that can entrain circadian rhythm. We recently showed that cancer survivors are willing and able to eat all their food within a 10-hour eating window-a practice called time-restricted eating. Herein, we are testing time-restricted eating against a control group (matched for time-, attention, and expectancy) to see if time-restricted eating can indeed alleviate cancer-related fatigue. All participants will be asked to use the myCircadianClock smartphone app to log their food intake and weekly body weight measurements. The participants assigned to the time-restricted eating group will be asked to eat all their food in a 10-hour window during the day. People can choose their start time based on their schedule and preferences, but we ask that the window is the same for the whole study (e.g., 7am-5pm,9:30am-7:30pm). Black coffee and unsweetened tea are allowed before the eating window, and water and medicines are allowed at all times. The participants in the control group will meet with a nutritionist to discuss the American Cancer Society nutrition guidelines in cancer survivorship; they will not be restricted to when they can eat. Participants in both groups will give us valuable information regarding how diet is related to the experience of fatigue. The purpose of this study is to test the effects of a 12-week TRE intervention vs. an unrestricted eating pattern on fatigue, the sustainability of the program at 24 weeks, and the effects of TRE on circadian rhythm and sugar metabolism.