Some people count calories. Others overhaul their menus. But this study suggests something entirely different: shift the timing.
In an experiment conducted at Northwestern School of Medicine, adults with overweight and elevated cardiometabolic risk were asked to stop eating three hours before bedtime, dim the lights and extend their overnight fast by about two hours. The result was measurable improvement in nighttime blood pressure, heart rate and glucose control, without reducing a single calorie.
The study, published last week in the journal Arteriosclerosis, Thrombosis, and Vascular Biology, adds to growing discussion around time-restricted eating. The focus is not only on how long people fast, but how well the fasting window aligns with sleep.
The broader context is concerning. According to preliminary U.S. data from 2017 to 2018, only 6.8% of adults met the criteria for optimal cardiometabolic health, defined as a state of lowered risk for chronic diseases such as Type 2 diabetes, nonalcoholic fatty liver disease and cardiovascular disease.
The 7.5-week trial included 39 adults ages 36 to 75, all with overweight or obesity. Participants were divided into two groups. The intervention group, about 80% of whom were women, extended their overnight fasting window to 13-16 hours. The control group maintained their usual eating habits, with a shorter fasting window of 11 to 13 hours.
Both groups were instructed to dim their lights three hours before bedtime. The key difference between the groups was meal timing and fasting duration, not the amount or composition of food.
Researchers sought to determine whether aligning the fasting window with the natural sleep-wake cycle and circadian rhythm could improve cardiovascular and metabolic markers. The circadian rhythm plays a central role in regulating the cardiovascular system and metabolism. The question, they said, is not only what people eat, but when, and how that timing corresponds with sleep.
The findings were notable. The intervention group experienced a 3.5% reduction in nighttime blood pressure and a 5% decrease in heart rate. Researchers said these changes reflect a healthier daily pattern, with higher levels during daytime activity and lower levels at night during rest, a pattern associated with better heart health.
Participants in the intervention group also showed improved glucose regulation the following day. When given glucose, their pancreases responded more efficiently, suggesting improved insulin response compared to the control group.
Dr. Daniela Grimaldi, the study’s first author and a researcher at Northwestern’s medical school, said timing the fasting window to align with the body's natural sleep and wake rhythms may improve coordination between the heart, metabolism and sleep, systems that work together to protect cardiovascular health.
Dr. Phyllis Zee, director of the Center for Sleep and Circadian Medicine, emphasized that the physiological benefits of time-restricted eating depend not only on how much and what people eat, but also on when they eat relative to sleep.
Further support for these findings appears in a scientific statement from the American Heart Association (AHA). The group’s experts concluded that meal timing matters. Late-night eating disrupts internal biological clocks, which are programmed to slow down in darkness. Consuming energy during typical sleep hours may adversely affect blood lipid profiles and promote insulin resistance and chronic inflammation, all well-established risk factors for heart attacks and stroke.
Unlike many previous studies that focused primarily on fasting duration, this trial emphasized alignment with sleep, a component critical to metabolic regulation. With high adherence rates of about 90%, researchers said synchronizing the fasting window with sleep may be a practical and accessible strategy to improve cardiometabolic markers without medication, particularly for middle-aged and older adults at elevated risk.