Research Answers to National Cancer Institute's (NCI) Provocative Questions

Intermittent energy restriction (IER) has been suggested to have important advantages over daily ER (DER) in producing sustained weight loss and reducing cancer risk. While IER is already being promoted in the general population to improve health and longevity, supportive evidence is urgently needed from rigorously conducted randomized trials. We propose a six-month randomized trial to demonstrate the superiority of IER over DER in reducing ectopic fat and total fat mass, and in improving cancer-related biomarkers and gut microbiome functions. Our previous work strongly suggests that ectopic fat, independently of total adiposity, plays an important role in the etiology of, and in the racial/ethnic disparities in, obesity-related cancers. We reported striking racial/ethnic differences in the strength of the association between body mass index (BMI) and risk of obesity-related cancers in the Multiethnic Cohort (MEC). We observed corresponding disparities in the propensity to accumulate visceral and liver fat among the same five ethnic groups in a recent MRI-based study and demonstrated an independent association of a robust biomarker-based visceral fat score with incident breast cancer in MEC. Additionally, we adapted an IER protocol combined with a Mediterranean dietary pattern (IER+MED) and demonstrated its feasibility, safety and greater efficacy over an active comparator (a hearthealthy DER approach) in reducing total and ectopic adiposity and improving beneficial gut microbiome functions in a 12-week randomized trial among 60 middle-aged adults of various Asian ethnicities with visceral obesity. We now propose the Healthy Diet and Lifestyle Study II, a 24-week randomized trial of IER+MED vs. MED/DER among 260 middle-aged Oahu adults of East-Asian, Pacific Islander or white ethnicity with VAT greater than the population median. The intervention will be delivered through 16 focused and customized consultations with research dietitians and will consist of an IER+MED (IER is 70% energy restriction on two consecutive days and a euenergetic MED diet for the other five days of the week) or the MED with a 20% daily energy restriction (MED/DER). Dietitians will monitor dietary compliance using the mobile food record (mFR) and compliance to a common physical activity recommendation using interviews and actigraphy throughout the intervention. We will compare IER+MED vs. MED/DER for reduction in MRI-measured visceral and liver fat and DXA-measured total adiposity (Aim 1) and for improvement in cancer-related biomarkers (IGF-1, IGFBP3, insulin, HOMA-IR, leptin, adiponectin, S HBG, hsCRP) and fecal metagenomic markers of microbial metabolite production (Aim 2). We will also investigate behavioral predictors of adherence to the prescribed IER, including psychosocial measures of self-efficacy and outcome expectancies, and dietary patterns based on timing and frequency of eating episodes (Aim 3). This study will provide robust effectiveness data for IER on lowering cancer related risk factors and inform future translational and dissemination research to reduce cancer risk in various US populations.

This application, in response to RFA-CA-004 “Research Answers to National Cancer Institute's (NCI) Provocative Questions (R01 Clinical Trial Optional),” will address “PQ2: How does intermittent fasting affect cancer incidence, treatment response, or outcome?” Obesity and age are two major risk factors for cancer development. Thus, therapeutic interventions that prevent or delay the development of excessive weight gain and/or age-associated physiological dysfunction hold great promise for reducing cancer risk in the increasingly obese and elderly global population. One such intervention is time-restricted eating (TRE), a pragmatic form of intermittent fasting in which daily caloric intake is constrained to a consistent window of 8–12 hours without explicitly reducing total caloric intake. In young male mice, time-restricted feeding (TRF) reduces cancer risk by preventing obesity and metabolic diseases. TRF has also been shown to reduce breast cancer xenograft progression in obese mice. In humans, short-term clinical studies of TRE have revealed metabolic improvements that predict reduced cancer risk, and epidemiological evidence suggests that prolonged nightly fasting can reduce the risk of cancer, independent of changes in body weight. This promising preliminary evidence suggests that TRE may be an effective intervention for reducing cancer risk. However, the effects of TRF in aged animals and in the context of an obesogenic Western diet have not yet been established, and the mechanisms by which TRF reduces cancer risk remain unknown. This application builds upon promising preliminary data and leverages the complementary skills of the research team to address these critical gaps in knowledge. Both obesity and aging are associated with mitochondrial dysfunction and the production of pro-tumorigenic mitochondrial metabolites. Proposed experiments test the hypothesis that TRF optimizes mitochondria function through both cell-autonomous and systemic mechanisms, thereby reducing cancer risk. In Aim 1, the impact of TRF on mitochondria function and related physiologies will be established in aged mice. Nutrient metabolism, energy consumption, and mitochondria function will be assessed in these mice. In Aim 2, an innovative combination of metabolomics and mitochondria respiration assays will be used to test the impact of TRF on mitochondria function in normal and cancer cells (assessing both cell-autonomous and non-cell-autonomous mechanisms). The effects of TRF on tumor incidence will be assessed by subjecting tumor-prone mice to TRF. In Aim 3, plasma collected from a recently concluded human TRE intervention study will be used to test the effect of TRE on mitochondria function and cancer risk in humans. The proposed comparative analysis of TRE in humans and mice will provide critical mechanistic insight into how one form of intermittent fasting can help prevent cancer onset and improve treatment outcomes.