But can you avoid those risks if you just stay up later?
Rather than what time you go to sleep, the study findings suggest that blood sugar control is tied to your body’s circadian rhythm (aka your internal clock), says the lead author, Daisy Duan, MD, an endocrinologist with a focus on diabetes and obesity at Johns Hopkins Medicine in Baltimore.
“Overall, it still appears it is best to avoid eating a late dinner, even if you don’t go to sleep right after,” says Dr. Duan.
The Study Looked at the Effects of Early and Late Dinners
To arrive at this conclusion, Duan and her colleagues recruited 13 healthy adults who were 25 years old, on average, and closely monitored them in a sleep lab.
To determine the start of each volunteer’s “biological night,” researchers measured their melatonin levels by testing their saliva. The body naturally produces this sleep-inducing hormone in response to nightfall.
“The time that melatonin levels start to rise is indicative of the start of your biological night,” says Duan, calling this method a “gold standard” for assessing a person’s circadian rhythms.
Researchers measured each participant’s glucose and insulin levels every hour for 24 hours via IV.
The scientists evaluated these measurements in three scenarios:
- When participants ate an early dinner (three hours before the start of their unique biological night), going to sleep five hours later
- When participants ate a late dinner (one hour after the start of their unique biological night), going to sleep one hour later
- When participants ate a late dinner (one hour after the start of their unique biological night), going to sleep five hours later
Volunteers were able to get eight full hours of sleep under all three scenarios, and they seemed to get the same quality of sleep no matter the circumstance. For dinner, they all got the same meals, with total calories based on each person’s weight.
The researchers compared blood glucose levels four hours after dinner from each of the three scenarios. They found that both late-dinner scenarios resulted in glucose levels that were 11 percent higher, on average, than the early-dinner scenario. Delaying sleep didn’t have an impact.
Study Has Some Limitations
Duan and her team emphasize that these study results are preliminary. They have not yet completed a full analysis of the data or submitted the results to a medical journal for peer review and potential publication.
Ajaykumar Rao, MD, a diabetes and metabolism endocrinologist with Temple Health in Philadelphia, who was not involved in the research, calls attention to several limitations of the analysis. It was conducted with a very small group of just 13 adults, in a very controlled environment that didn’t reflect real-life behaviors. Also, the study was very short, so it may not reflect the long-term effects of late eating or late sleeping.
Because the study included only healthy young adults, he views the findings as more applicable to preventing diabetes rather than suggesting lifestyle changes for people who already have diabetes.
“The results suggest that the cumulative effects of eating late put people at risk for eventually developing insulin resistance, which is a precursor to diabetes,” says Dr. Rao.
“When you eat later, your body’s response to a glucose load may be a bit dampened because your own insulin levels are not attacking that meal the same way they would otherwise,” he says.
Your Body’s Natural Rhythms Should Determine When You Eat and Sleep
For Theresa Gentile, RDN, a spokesperson for the Academy of Nutrition and Dietetics, the study highlights the importance of being in tune with your own circadian clock.
“You should try to pay attention to your body’s natural rhythms by noting when you start to feel sleepy in the evening,” says Gentile, who was not involved in the research. “Aim to finish dinner at least a few hours before this time.”
She suggests two ways to get a better handle on your circadian rhythms. “A registered dietitian-nutritionist can help you track your typical sleep and hunger patterns,” she says. “Or you can use tools like wearable sleep trackers to help identify the start of your personal biological night, so you can time meals and sleep for optimal health.”