Researchers at Northwestern Medicine investigated whether adjusting the nighttime fasting period to a person’s natural sleep-wake cycle could improve heart and metabolic health. The circadian rhythm plays a central role in regulating cardiovascular and metabolic functions. Importantly, participants did not reduce their calorie intake. The focus was solely on adjusting meal times.

The study found that middle-aged and older adults at increased risk for cardiometabolic disease benefited from extending their nighttime fasting period by about two hours. They also refrained from eating three hours before bedtime and dimmed the lights. These changes led to measurable improvements in heart and metabolic markers during sleep and throughout the following day.

How Fasting Before Bedtime Promotes Heart Function

The results of the study can be explained by the body’s internal clock, known as the circadian rhythm. Our bodies are programmed to carry out certain metabolic and regenerative processes at fixed times of the day. When adults eat their last meal three hours before bedtime, insulin levels and metabolic processes begin to adjust to the nighttime rest phase. This improves blood sugar control because the body processes energy more efficiently and supports fat burning overnight. At the same time, dimming the lights in the evening has a positive effect on melatonin production, the hormone that induces sleep. A stable sleep-wake rhythm helps to normalize blood pressure and heart rate. It is important to note that these effects do not depend on calorie reduction; the timing of food intake and alignment with the natural internal clock are crucial. The combination of an earlier dinner, a longer nighttime fasting period, and dimmed lighting allows the body to regenerate optimally at night, which noticeably improves cardiovascular health and blood sugar regulation.

“Aligning our fasting window with the body’s natural wake-sleep rhythm can improve coordination between the heart, metabolism, and sleep, all of which work together to protect cardiovascular health,” said first author Dr. Daniela Grimaldi, a research fellow in neurology in the Division of Sleep Medicine at Northwestern University Feinberg School of Medicine. The results were published in Arteriosclerosis, Thrombosis, and Vascular Biology, a journal of the American Heart Association. “For the physiological benefits of time-restricted eating, it’s not just how much and what you eat that matters, but also when you eat in relation to sleep,” said corresponding author Dr. Phyllis Zee, director of the Center for Circadian and Sleep Medicine and head of sleep medicine in the Department of Neurology at Feinberg.

Why Cardiometabolic Health Matters

Previous data show that only 6.8% of adults in the US had optimal cardiometabolic health between 2017 and 2018. Poor cardiometabolic health increases the risk of chronic diseases such as type 2 diabetes, non-alcoholic fatty liver disease, and cardiovascular disease.

Time-restricted eating has gained popularity as studies suggest it can improve cardiometabolic markers and sometimes match the benefits of traditional calorie-restricted diets. However, most research has focused on how long people fast, rather than how well that fasting window aligns with sleep timing, which is critical for metabolic regulation.

Given nearly 90% adherence in this study, the researchers believe that anchoring time-restricted eating to the sleep phase may be a realistic and accessible non-pharmacological approach, particularly for middle-aged and older adults who are at higher cardiometabolic risk. The team plans to refine this protocol and expand testing in larger multicenter studies.

Improvements in Blood Pressure, Heart Rate, and Blood Sugar

The 7.5-week study compared individuals who stopped eating at least three hours before bedtime with those who maintained their usual eating habits. Those who adjusted their eating times experienced several significant changes. Nighttime blood pressure decreased by 3.5% and heart rate by 5%. These changes reflected a healthier daily pattern, with heart rate and blood pressure rising during daytime activities and falling at night during rest. A stronger day-night rhythm is associated with better cardiovascular health.

Participants also showed improved blood sugar control during the day. When given glucose, their pancreas responded more effectively, indicating improved insulin release and more stable blood sugar levels. The study involved 39 overweight/obese adults (aged 36 to 75). Participants were assigned to either a group with extended nighttime fasting (13 to 16 hours of fasting) or a control group that maintained their usual fasting window (11 to 13 hours). Both groups dimmed the lights three hours before bedtime. The intervention group consisted of 80% women.

Measures to Support Heart Health Optimally

Daily structure plays a central role in protecting heart health while taking the circadian rhythm into account. A regular sleep-wake rhythm, where you go to bed and get up at the same time every day, stabilizes blood pressure and heart rate and reduces inflammatory processes. Ideally, the last meal should be eaten at least three hours before bedtime, which extends the nighttime fasting period and improves blood sugar levels and cardiovascular parameters. Light management is another important factor: soaking up natural light in the morning synchronizes the internal clock, while dim light in the evening promotes melatonin production and supports healthy sleep.

Physical activity should preferably take place in the morning or at noon to activate the metabolism without disturbing sleep. Stress management through relaxation exercises in the evening can improve heart rate variability, while controlled consumption of caffeine and alcohol does not interfere with the circadian rhythm. Slight cooling in the evening (room temperature 18–20°C) supports sleep, lowers the heart rate, and relieves the heart. It is also advisable to drink water during the day and slightly reduce fluid intake in the evening to avoid nighttime trips to the bathroom and not disturb sleep. Last but not least, regular daily activities, social contacts, and fixed rituals can stabilize the internal clock and reduce stress, which protects the heart.