Assessing successful completion of calorie restriction studies for the prevention and treatment of cancer

Objectives: Calorie restriction (CR) >20% has been hypothesized to aid cancer prevention and treatment. Yet, to our knowledge, there is a lack of reported studies in humans describing tolerance, adherence, or efficacy, and unpublished and incomplete dietary studies may indicate lack of tolerability and compliance. The aim of this study was to assess registered clinical trials using CR for cancer treatment and prevention, rates of completion, and published reports to determine whether barriers to publication may be indicative of either negative studies, or incompletion due to unreported compliance issues. Methods: Current registered clinical trials assessing CR in cancer prevention and treatment were assessed at clinical-trials.gov and the International Clinical Trials Registry at the World Health Organization. Assessment of study completion and publication was calculated and compared with methods of CR used, as were rates of inactive and incomplete studies, dormant studies, time of dormancy, type of study, and generalizable conclusions. Results: Twenty-nine trials were registered assessing CR in cancer treatment or prevention. Of these studies, 18 met initial criteria, and only 4 had completed and published results. Three of these tested a CR regimen incorporating exercise or intermittent restriction. Target CR ranged from 500 to 1000 kcal/d, with one study aim of 20% CR; no study reported rates of actual calorie intake. The majority of dormant and unpublished studies (69%) used general dietary CR and was without update ranging from 265 to 2518 d. Only one study reported on the side effects of the CR regimen; compliance and adherence to the regimen was described in the four completed studies that reported results. Only two studies were registered as pilot studies testing the feasibility of CR. Conclusions: Poor completion and lack of reporting of results is apparent in the majority of studies assessing CR for cancer prevention or treatment. These findings should be considered during the design of future studies assessing dietary strategies for cancer prevention or treatment. (C) 2020 Elsevier Inc. All rights reserved.