Researchers from Northwestern University School of Medicine confirm that adjusting meal times to the body's biological clock, especially the timing of dinner in relation to sleep, can directly impact heart health, sleep quality, and brain function.
Dr. Phyllis Zee, lead author of the study and a sleep medicine expert at Northwestern University, explains, "It's not just what we eat, but also when we eat it in relation to sleep, which is a key factor in the physiological benefits of food."
The idea of the study is based on the “three-hour rule,” which includes stopping eating at least three hours before bedtime, with the timing of dinner varying according to the personal bedtime; those who go to bed at nine in the evening prefer to finish their dinner before six, while those who go to bed at eleven can eat dinner until eight in the evening.
On the other hand, eating close to bedtime may lead to increased stomach acidity and heartburn, and keep the body active, which hinders sleep quality, in addition to the possibility of disrupting the biological clock and difficulty falling into deep sleep.
The study included 39 participants aged between 36 and 75, mostly women, who were overweight or obese, in addition to early indicators of heart and metabolic risks such as high blood sugar and glycated hemoglobin (A1c) levels.
Participants with diabetes, sleep disorders, or severe mental illness were excluded. They were randomly divided into two groups: one group that fasted for at least three hours before bedtime, and a control group that maintained their usual eating habits.
The study period lasted for seven weeks, during which participants adhered to their dietary schedule at home, with accurate measurements taken before and after the experiment, including blood pressure, heart rate, cortisol levels, and glucose tolerance tests.
The results showed a clear improvement in the group that stopped eating early; the heart rate during sleep decreased, and its normal decrease improved by approximately 5%, and the diastolic blood pressure decreased by 3.5%.
The same group also showed an improvement in the body's response to sugar, with a significant decrease in glucose levels after consuming a sugary drink, and an improvement in insulin secretion during the first minutes of the test.
A 12% decrease in nighttime cortisol levels was also recorded, indicating a reduction in the stress hormone and improved hormonal stability during the night.
The results show that the body has a biological rhythm that affects how it deals with food; insulin sensitivity is higher in the morning, making the body more efficient at dealing with food, while this regulation decreases at night with the rise of the hormone melatonin, which prepares the body for sleep and reduces insulin secretion.
Eating late disrupts this balance, which negatively affects blood sugar levels and the health of blood vessels.
The study indicates that better sleep resulting from eating earlier helps the brain get rid of metabolic waste, including proteins associated with Alzheimer's and Parkinson's diseases, and also contributes to better blood sugar regulation, which reduces damage to the brain's microvascular system and limits cognitive decline.
Controlling weight by reducing nighttime eating also contributes to improved brain health, as obesity is linked to an increased risk of dementia.
