For years, intermittent fasting has been touted as a path to improved health, but a growing body of research suggests that when you fast may be just as important as how long. A new study from Northwestern Medicine reveals that aligning overnight fasting with an individual’s natural sleep-wake cycle—their circadian rhythm—can lead to significant improvements in cardiovascular and metabolic health, without requiring changes to overall calorie intake.
The research, published in Arteriosclerosis, Thrombosis, and Vascular Biology, a journal of the American Heart Association, focused on middle-aged and older adults at higher risk for cardiometabolic disease. Participants who extended their overnight fast by approximately two hours, and refrained from eating for three hours before bedtime, experienced notable benefits. These included a 3.5% dip in nighttime blood pressure and a 5% reduction in nighttime heart rate – both indicators of a healthier cardiovascular system.
“Timing our fasting window to work with the body’s natural wake-sleep rhythms can improve the coordination between the heart, metabolism and sleep, all of which work together to protect cardiovascular health,” explained Dr. Daniela Grimaldi, research associate professor of neurology in the division of sleep medicine at Northwestern University Feinberg School of Medicine, and first author of the study.
The study’s findings are particularly relevant given the concerning statistics surrounding cardiometabolic health in the United States. Previous research indicates that only 6.8% of U.S. Adults had optimal cardiometabolic health between 2017 and 2018. Poor cardiometabolic health increases the risk of chronic illnesses such as type 2 diabetes, non-alcoholic fatty liver disease, and cardiovascular diseases.
Traditionally, much of the research on time-restricted eating has centered on the duration of the fasting period, rather than its alignment with the body’s internal clock. This new study highlights the importance of considering the circadian rhythm, a key regulator of cardiovascular and metabolic function. “It’s not only how much and what you eat, but also when you eat relative to sleep that is important for the physiological benefits of time-restricted eating,” said Dr. Phyllis Zee, director of the Center for Circadian and Sleep Medicine and chief of sleep medicine in the department of neurology at Feinberg, and the study’s corresponding author.
The 7.5-week study involved 39 overweight or obese participants, aged 36 to 75. Participants were divided into two groups: an extended overnight fasting group (fasting for 13 to 16 hours) and a control group (maintaining their usual 11 to 13-hour fasting routine). Both groups were instructed to dim the lights three hours before bedtime. The intervention group was comprised of 80% women.
Beyond the improvements in blood pressure and heart rate, the extended fasting group also demonstrated better daytime blood sugar control. Their pancreas exhibited a more efficient response to glucose challenges, suggesting improved insulin sensitivity and more stable blood sugar levels. This is a crucial finding, as impaired blood sugar control is a hallmark of type 2 diabetes and a significant risk factor for cardiovascular disease.
The study authors noted that the high adherence rate – nearly 90% – suggests that this sleep-aligned approach to time-restricted eating may be more sustainable and accessible than other methods. Leveraging the sleep period as an anchor for fasting timing could be a particularly effective strategy for middle-aged and older adults, who are at increased risk for cardiometabolic disease.
While the findings are promising, it’s important to note that this is a preliminary study. The researchers plan to refine their protocol and conduct larger, multi-center trials to confirm these results and explore the long-term effects of sleep-aligned fasting.
It’s also crucial to remember that time-restricted eating is not a one-size-fits-all approach. Individuals with underlying health conditions, or those taking medications, should consult with their healthcare provider before making any significant changes to their diet or eating patterns.
The study was funded by the National Heart Lung and Blood Institute, the National Institute of Aging, and the National Center for Advancing Translational Sciences, all part of the National Institutes of Health.
