Delayed dinnertime impairs glucose tolerance in healthy young adults.

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• Eating dinner later than 19:00 may impact the body’s ability to manage blood sugar after a meal.

• Delaying dinner by just 1 hour may lead to higher blood glucose levels.

• Meal timing may play an important role in short-term glucose regulation, even in healthy young adults.

Introduction

This study aimed to investigate the relationship between dinnertime delay, hourly up to 3 h, on the subsequent glucose fluctuations in healthy adults.

Methods

This was a 14-day open-label, randomised, cross-over trial with fixed mealtimes at 7:00 (breakfast), 13:00 (lunch), and 19:00 (dinner; 19D). On intervention days, dinner was consumed at 20:00 (20D), 21:00 (21D), or 22:00 (22D), in random order, with only water, tea, or non-sweetened coffee permitted outside mealtimes. Interstitial glucose was measured every 15 minutes using intermittently scanned continuous glucose monitoring. Data from specified intervention days were used for comparative glucose analyses.

Results

• Compared with the 19:00 dinner condition (19D), dinners consumed at 20:00, 21:00, and 22:00 were associated with impaired postprandial glucose tolerance, characterised by higher glucose peaks and a delayed return to baseline.

• Postprandial glucose concentrations and incremental area under the curve from 0–180 min (iAUC₀–₁₈₀) were significantly higher for 20D, 21D, and 22D than for 19D.

• The postprandial glucose peak was significantly higher in the 21D condition compared with 19D.

• No significant differences in postprandial glucose parameters were observed among 20D, 21D, and 22D, indicating similar glycaemic responses across these later dinner times.

• Mean 24-h glucose, glucose standard deviation, coefficient of variation, and mean amplitude of glycaemic excursions did not differ significantly between conditions, except for a higher 24-h average glucose in the 20D condition.

• Analysis of glucose levels between 19:00 and 25:00 and corresponding iAUC₁₉–₂₅h supported poorer glucose tolerance with dinners later than 20:00.

• Findings suggest that factors beyond circadian regulation alone may contribute to glucose intolerance after 20:00, as no further deterioration was observed between 20:00 and 22:00.

Conclusion

A delay of as little as 1 hour in dinnertime may impair postprandial glucose tolerance in healthy young adults.

• Encouraging earlier evening meals (around 19:00) may help support optimal postprandial glucose control.

• Meal timing should be considered alongside diet quality in glycaemic management strategies.

• Longer-term intervention studies are needed to determine whether the observed acute effects persist over time.

• Future research could include populations with metabolic disorders to improve generalisability.

• Larger, adequately powered trials are required to explore potential sex-based differences.

• Future studies could standardise meal energy content and more tightly control physical activity.

• Mechanistic studies examining alternative meal timings, macronutrient composition, and related metabolic markers (e.g., free fatty acids, GLP-1) are warranted to better understand the pathways influencing postprandial glucose responses.