Participants stopped eating and lowered the lights three hours before bedtime, extending their overnight fast by about two hours without cutting calories.

• Compared with the control group, nighttime blood pressure dropped by 3.5% and heart rate fell by 5%, signaling a healthier pattern during sleep.
• With nearly 90% of participants sticking to the plan, researchers say this simple shift in meal timing could be an accessible, non-drug approach to improving cardiometabolic health.
• As the study authors emphasize, “It’s not only how much and what you eat, but also when you eat relative to sleep that is important.”

Researchers at Northwestern Medicine tested a new way to personalize overnight fasting by timing it to match each person’s natural sleep-wake cycle, which plays a central role in regulating heart and metabolic function. Importantly, participants did not reduce calories. Instead, the focus was on when they ate.

The findings showed that middle-aged and older adults at elevated risk for cardiometabolic disease benefited from extending their overnight fast by about two hours. They also stopped eating and dimmed lights three hours before bed. This adjustment improved measures of heart and metabolic health both overnight and during the following day.

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

The study will be published today (February 12) in Arteriosclerosis, Thrombosis, and Vascular Biology, a journal 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 chief of sleep medicine in the department of neurology at Feinberg.

Why Meal Timing Matters for Cardiometabolic Health

Earlier research has shown that only 6.8% of U.S. adults had optimal cardiometabolic health in 2017 to 2018. Poor cardiometabolic health increases the risk of chronic conditions such as type 2 diabetes, non-alcoholic fatty liver disease, and cardiovascular disease.

Time-restricted eating has gained popularity because studies suggest it can improve cardiometabolic markers and, in some cases, rival traditional calorie-restricted diets. However, most research has focused on the length of the fasting window rather than how that window aligns with sleep timing, which is a critical component of metabolic regulation.

Because nearly 90% of participants followed the plan successfully, researchers believe anchoring fasting to the sleep period may be a more realistic, non-pharmacological strategy for improving cardiometabolic health, particularly for middle-aged and older adults at higher risk.

The team plans to refine the approach and test it in larger, multi-center trials.

Improved Blood Pressure, Heart Rate, and Blood Sugar

The 7.5-week study compared people who stopped eating at least three hours before bedtime with those who maintained their usual routines. Those who adjusted their timing experienced several measurable benefits.

Nighttime blood pressure decreased by 3.5%, and heart rate dropped by 5%. These changes reflected a healthier daily rhythm, with heart rate and blood pressure rising appropriately during daytime activity and falling at night during rest. A stronger day-night pattern is associated with better cardiovascular outcomes.

Participants also showed improved daytime blood-sugar control. When given glucose, their pancreas responded more efficiently, indicating better insulin release and steadier blood sugar levels.

The study included 39 overweight/obese adults (36 to 75 years old). Participants were assigned either to an extended overnight fasting group (13 to 16 hours of fasting) or to a control group that maintained a habitual fasting window (11 to 13 hours). Both groups dimmed lights three hours before bedtime. The intervention group consisted of 80% women.