MedicalResearch.com Interview with:
Benjamin D. Horne, PhD, MPH, FAHA, FACC
Director, Cardiovascular and Genetic Epidemiology, Intermountain Heart Institute
Adjunct Assistant Professor, Genetic Epidemiology Division, Department of Medicine,
University of Utah
Medical Research: What is the background for this study? What are the main findings?
Dr. Horne: A rapidly expanding set of results from animal studies exists regarding the effects of intermittent fasting among animals. Many pilot studies of intermittent fasting have been performed now, too, but the body of literature regarding the human response to fasting is incomplete. This study sought to determine how preliminary and incomplete the evidence is in humans regarding the health benefits and the harmful side-effects of intermittent fasting. The purpose was to determine how reliable the evidence is that people should be engaging in fasting to improve their health. In particular, one major concern is that diet gurus and even some scientists are marketing intermittent fasting to the public through diet books and other methods that produce additional income for them, but it is unclear whether their claims can be supported.
The main findings of the study are that only three controlled clinical trials of intermittent fasting in humans have been published that were designed rigorously and included a control group in addition to the fasting intervention arm of the study. One of the three had a pre-specified primary outcome (weight loss) and another used the Bonferroni correction to account for inflated false positive results due to multiple hypothesis tests (the third study unfortunately did neither, which is the common approach in human studies of intermittent fasting). These three controlled trials only used surrogate or intermediate endpoints, though, such as weight, cholesterol, or other risk factors for disease. The three trials also have substantial limitations, including small sample sizes (~30 people total), a fasting regimen that was studied for less than three months, and no evaluation of clinical safety outcomes. Only one of the three trials was registered on ClinicalTrials.gov, a site instituted as part of the FDA Modernization Act and a pre-requisite for trials that are published in scientifically sound medical journals and are to be reviewed by the FDA.
Two observational studies of the association of intermittent fasting with clinical events (i.e., coronary artery disease diagnosis and diabetes diagnosis) also have been published. These two studies included 200 patients and 445 patients. They were performed in patients drawn from a general population in which a large proportion of people engage in fasting intermittently over a period of decades. These observational studies provide the only evidence that fasting is associated with a lower risk of disease outcomes. Such studies are limited, though, by adjustment for only known or measured confounders, making it possible that some important factors may be unobserved in the studies that would account for the fasting benefit that was observed. No randomized controlled clinical trial of fasting for clinical events or disease outcomes has been performed, though, thus these five studies are the whole body of reliable evidence that intermittent fasting is beneficial to humans.