The effect of meal timing on postprandial glucose and insulin response in healthy volunteers
Authors: Bonham Maxine , Leung Gloria KW , Huggins Catherine E 
Published: November 2023

Introduction

Shift workers are at increased risk of chronic conditions including obesity, cardiovascular diseases and type‐2 diabetes. Compared with a meal consumed during day hours, a meal consumed during the night triggers an exaggerated postprandial glucose response and reduced sensitivity to insulin. There is evidence to suggest that small changes in the type of food consumed at night can positively impact these responses. The aim of this study, therefore, was to investigate the postprandial glucose response to i) an oral glucose load (Test One) and ii) a low glycaemic index (GI) challenge (Test Two), in the morning compared to night in healthy volunteers.

Methods

Participants fasted for 10 hours before each meal in each test. Test one participants (n=10) consumed a glucose solution (75 g in 400 mL) at 8am and 8pm. Test two participants (n=9) consumed a low GI meal at 8am, 8pm and midnight. Postprandial glucose responses were collected at seven time points over two hours (Test One) and postprandial glucose and insulin responses were collected at nine time points over three hours (Test Two). Five participants completed both Test One and Two. Incremental AUC (iAUC) was calculated using the trapezoidal rule and significance tested using Wilcoxon‐signed rank. A p‐value <0.05 was taken as significant.

Results

Participant characteristics and postprandial responses are reported in Table one. For Test One no differences were observed in fasting glucose when morning was compared to night (p = 0.475), whereas glucose iAUC was significantly higher at night compared to the morning (p= 0.007). In Test Two no differences in fasting glucose (p=0.819) or insulin was observed (p= 0.196) between the three time points. Glucose iAUC at midnight and 8pm were both greater than 8am (p = 0.021; p = 0.008) but not between 8pm and midnight (p = 0.594). The same findings were observed for postprandial insulin with higher responses observed at 8pm (p=0.008) and midnight (p=0.008) compared to the morning. No significant difference was observed between the midnight and evening response (p = 0.374).

Conclusion

These findings confirm circadian differences in the response to eating. More importantly, it warrants further research into identifying both the optimal timing of meal intake and meal composition, for people who have no choice but to eat late at night.

Support or Funding Information

No funding was provided for this research

The effect of meal timing on postprandial glucose and insulin responses after an oral glucose load (n=10) and low glycaemic index (GI) meal (n=9) in healthy volunteers.

Oral glucose load
Low glycaemic index (GI) challenge

Gender
8 female, 2 male
7 female, 2 male

Median (IQR)
Median (IQR)

Age (years)
23 (4)
26 (15)

BMI (kg/m2)
22.6 (3.0)
23.6 (3.9)

Waist circumference (cm)
72.4 (9.2)
74.5 (4.8)

0800h
2000h
0800h
2000h
0000h

Fasting glucose (mmol/l)
4.7 (0.6)
4.8 (0.6)
5.0 (0.7)
4.8 (0.7)
5.1 (0.8)

Fasting insulin (mU/L)
‐
7.4 (6.6)
3.8 (5.5)
4.1 (2.6)

Postprandial glucose iAUC (mmol/L.2h)
181 (160)
332 (166)*
‐
‐
‐

Postprandial glucose iAUC (mmol/L.3h)

28 (41)
176 (331)*
253 (85)*

Postprandial insulin iAUC (mU/L.3h)
‐
1404 (885)
3288 (1845)*
2945 (3665)*

Significantly different from morning; p<0.05