Effects of Earlier Dinner Times on Glycemic Control

A recent study showed that it might be a good idea to start eating dinner earlier in the day to help keep glycemic levels in control.

Growing up, you might have heard from your family that it isn’t good to eat food when it is close to bedtime. Retrospectively, they may have had the right idea. Eating later in the night may cause a variety of adverse effects like weight gain and metabolic dysfunctions. One meta-analysis even saw a 10% increase in the risk of developing type 2 diabetes in people who partake in shift work. A possible reason for this may be due to impaired insulin secretion caused by disrupting the circadian rhythm. With all things considered, the timing of the last meal of the day may play a prominent role in glycemic variability. Many studies compared the effects of early dinner times vs. late dinner times on blood glucose (BG) levels, but very few looked at how timing affects BG over 24 hours. 

A recent randomized cross-over trial used continuous glucose monitoring to assess the effects of eating dinner earlier (18:00, or 6 PM) rather than later (21:00, or 9 PM). Subjects over 20 years old with no history of smoking or major diseases participated in the 3-day study. Everyone wore a continuous BG monitor and accelerometer from the day before the experiment until the end of day 3. The investigators instructed the subjects to eat a prescribed diet at designated times throughout the day and randomly assigned them to eat an early or late dinner. After dinner, the only thing they could consume was water. On day 1, subjects ate their scheduled meals under normal conditions. They then returned to the laboratory on days 2 and 3 to be observed under laboratory conditions while eating. In the laboratory during days 2 and 3, the investigators recorded their height, weight, and BMI before breakfast and gave them their meals for the day. The subjects also filled out an evaluation form multiple times during the day to assess their hunger, fullness, desire to eat, and capacity to eat.

Meanwhile, the continuous BG monitor would record their BG levels every minute. To assess for efficacy, the authors calculated the average BG level every 15 minutes, the mean amplitude of glycemic excursions (MAGE), the mean postprandial level up to 3 hours after meals, and the incremental AUC (iAUC) and compared them between the two groups. Additional outcomes included physical activity (step count), sleep time, and energy expenditure/substrate oxidation (measured using indirect calorimetry). The authors only analyzed data from days 2 and 3 as meals from the day before day one could have affected the results. To do this, they used ANOVA and paired t-tests to compare the two groups with a significance level of 0.05. 

By the end of day 3, 12 of 14 subjects completed the study, with one dropping out from illness and the other due to schedule conflicts.  Both groups had comparable height, weight, and BMI throughout the study. When comparing the timing effects on blood glucose, the authors found that eating dinner earlier led to significant reductions in MAGE from days 1 to 3 (-8±9 mg/dL; p=0.027). In addition, subjects who ate earlier dinners had lower mean BG levels throughout the day (p=0.010) and throughout the night to early morning (from 18:00 to 06:00). Timing also appeared to affect postprandial levels, as iAUC measurements for postprandial BG were higher after dinner but not breakfast or lunch in the late dinner group (p<0.001).

Regarding appetite, subjects who ate earlier dinners recorded higher scores for desire/capacity to eat and hunger later in the night (23:00). Overall, there were no differences in energy expenditure or substrate oxidation. Still, they did see reductions in postprandial respiratory quotient up to 1 hour after breakfast in the early dinner group (p<0.05). Finally, there were no significant differences in sleep or physical activity. 

Based on these findings, eating dinner earlier by at least 3 hours may improve 24-hour glycemic control. Specifically, earlier dinner times can help reduce post-dinner BG levels and reduce glycemic variability throughout the night. While these patients were healthy with no chronic conditions, other studies suggest that early time-restricted feeding may improve insulin sensitivity and reduce the risk of developing diabetes. Given what we know, early time-restricted feeding might be an excellent nonpharmacological strategy for patients who need additional help with glycemic control.

Practice Pearls

• Having an early dinner can help with 24-hour glycemic control, especially right after dinner. 
• A significant barrier to this strategy may be an increase in appetite as the night goes on.
• Further research is needed to see how this strategy will benefit patients with diabetes.

Nakamura, Kaho et al. “Eating Dinner Early Improves 24-h Blood Glucose Levels and Boosts Lipid Metabolism after Breakfast the Next Day: A Randomized Cross-Over Trial.” Nutrients vol. 13,7 2424. 15 Jul. 2021, doi:10.3390/nu13072424

Gao, Yinyan et al. “Association between shift work and risk of type 2 diabetes mellitus: a systematic review and dose-response meta-analysis of observational studies.” Chronobiology international vol. 37,1 (2020): 29-46. doi:10.1080/07420528.2019.1683570

Sutton, Elizabeth F et al. “Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes.” Cell metabolism vol. 27,6 (2018): 1212-1221.e3. doi:10.1016/j.cmet.2018.04.010

Andy Dao, PharmD Candidate, University of South Florida Taneja College of Pharmacy