Aligning overnight fasting with sleep improves heart health

A new Northwestern Medicine study has personalized overnight fasting by aligning it with individuals' circadian sleep-wake rhythm - an important regulator of cardiovascular and metabolic function - without changing their caloric intake. 

The study found that among middle-age and older adults who are at higher risk for cardiometabolic disease, extending the participants' overnight fast by about two hours, dimming the lights and not eating for three hours prior to bedtime improved measures of cardiovascular and metabolic health during sleep, as well as during the daytime. 

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."

Dr. Daniela Grimaldi, first author, research associate professor of neurology, division of sleep medicine at Northwestern University Feinberg School of Medicine

The study will be published Feb. 12 in the journal Arteriosclerosis, Thrombosis, and Vascular Biology, part of the American Heart Association.

"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 corresponding author Dr. Phyllis Zee, director of the Center for Circadian and Sleep Medicine and the chief of sleep medicine in the department of neurology at Feinberg.

Previous research has found only 6.8% of U.S. adults had optimal cardiometabolic health in 2017 to 2018. Poor cardiometabolic health can lead to chronic illness, including type 2 diabetes, non-alcoholic fatty liver disease and cardiovascular diseases.

Time-restricted eating has continued to surge in popularity because research has shown it can improve cardiometabolic health and rival traditional calorie‑restricted diets, but most studies have focused on how long people fast, not how their fast lines up with their sleep schedule - a key factor in metabolic regulation.

Given the nearly 90% adherence rate in the study, the study's novel approach of leveraging the sleep period as an anchor for the timing of time-restricted eating may be a more accessible non-pharmacological strategy for improving cardiometabolic health, particularly in middle-aged and older adults who are at higher risk for cardiometabolic disease, the study authors said.

The study authors said they plan refine the protocol from this study and take it to larger multi-center trials. 

Improved blood pressure, heart rate, blood-sugar control

In the 7.5‑week study, people who finished eating at least three hours before going to bed saw meaningful improvements compared with those who kept their usual eating routines. They experienced:

• Improved nighttime patterns in blood pressure (dipping by 3.5%) and heart rate (dipping by 5%): Their bodies showed a more natural drop in both measures during sleep, which is an important sign of cardiovascular health. Notably, their hearts beat faster during the day when they were active and slowed at night when they were resting. A stronger day-night pattern is linked to better cardiovascular health.
• Better daytime blood‑sugar control: Their pancreas responded more efficiently when challenged with glucose, suggesting it could release insulin more effectively and keep blood sugar steadier.

In the study, 39 overweight/obese participants (36 to 75 years old) completed either an extended overnight fasting intervention (13 to 16 hours of fasting) or a control condition (habitual fast of 11 to 13 hours). Both groups dimmed the lights three hours before bedtime. The intervention group consisted of 80% women.