by Lewis Chang, PhD
Intermittent fasting is an eating pattern where one alternates periods of eating and fasting. Overall, intermittent fasting has demonstrated efficacy in weight management and improvements in metabolism and body composition.1,2 However, it is unclear whether the observed metabolic benefits are the result of weight loss or due to other mechanisms. Also, there are a variety of fasting regimens which may have different physiological effects.
Researchers from The University of Alabama at Birmingham (Birmingham, AL) Department of Nutrition conducted a controlled feeding trial aimed to understand whether intermittent fasting was still beneficial in the absence of weight loss.3 The participants were 8 men who were overweight and had prediabetes. The method of intermittent fasting was termed early time-restricted feeding (eTRF)—eating three meals within six hours early in the day (before 3 pm) in order to be in alignment with circadian rhythms in metabolism, followed by 18 hours of fasting until the next meal.3 Each subject was randomized to eTRF (6-hour feeding and 18-hour fasting) or a control schedule (12-hour feeding and 12-hour fasting) for 5 weeks and, after a 7-week washout period, crossed over to the other schedule for 5 weeks.3 Under supervision, participants consumed all the meals provided by the study, and the food provided sufficient calories to maintain their body weight.
Compared to the control schedule, eTRF (1) dramatically reduced insulin levels and improved insulin sensitivity and β cell function, (2) significantly lowered both systolic and diastolic blood pressure, (3) improved plasma levels of 8-isoprostane (a marker of oxidative stress), (4) significantly reduced appetite in the evening.3
This study clearly demonstrated the cardiometabolic benefits of intermittent fasting in a group of men at greater risk of developing diabetes, even without weight loss. However, the investigators noticed an increase in morning fasting levels of triglycerides after eTRF that warrants further investigation. Also, eating all three meals within 6 hours was challenging according to some study participants. The study investigators suggest that eating three meals within 8 hours followed by 16 hours of fasting may be a more feasible routine for future trials.
Why is this Clinically Relevant?
- Intermittent fasting has demonstrated efficacy in weight management and improvements in various cardiometabolic endpoints1-3
- For individuals with prediabetes, a type of intermittent fasting called early time-restricted feeding (eating all three meals in six hours early in the day followed by 18 hours of fasting) may improve insulin sensitivity, oxidative stress, and blood pressure, and reduce appetite3
- Horne BD, Muhlestein JB, Anderson JL. Health effects of intermittent fasting: hormesis or harm? A systematic review. Am J Clin Nutr. 2015;102(2):464-470.
- Stockman MC, Thomas D, Burke J, Apovian CM. Intermittent fasting: is the wait worth the weight? Curr Obes Rep. 2018;7(2):172-185.
- Sutton EF, Beyl R, Early KS, Cefalu WT, Ravussin E, Peterson CM. Early time-restricted feeding improves insulin sensitivity, blood pressure, and oxidative stress even without weight loss in men with prediabetes. Cell Metab. 2018;27(6):1212-1221 e1213.