Time of day difference in postprandial glucose and insulin responses: Systematic review and meta-analysis of acute postprandial studies.
Level 1 - systematic review of randomized trials
Systematic review and meta-analysis of controlled within-subject crossover feeding studies
PubMed 31782659 · doi:10.1080/07420528.2019.1683856
What was done
Authors conducted a systematic review and meta-analysis across seven electronic databases searched through February 2018. Eligible studies evaluated healthy adults who consumed identical test meals during both daytime (07:00–16:00) and nighttime (20:00–04:00) after a minimum 3-hour fast. The primary outcome measures were postprandial glucose and insulin area under the curve (AUC) or incremental AUC (iAUC). Fifteen studies met the inclusion criteria, and 10 were included in the quantitative meta-analyses.
What was found
Meta-analysis demonstrated a significantly lower postprandial glucose response in the daytime compared to nighttime following an identical meal (SMD = -1.66; 95% CI, -1.97 to -1.36; p < .001). Daytime postprandial insulin response was also significantly lower than at night (SMD = -0.35; 95% CI, -0.63 to -0.06; p = .016). Studies ineligible for quantitative synthesis qualitatively supported lower daytime glucose, but qualitative findings for insulin were inconsistent.
Why it matters
This meta-analysis demonstrates that human glucose tolerance is significantly impaired during the biological night compared to daytime. These circadian metabolic differences offer a physiological mechanism linking habitual night eating and shift work to higher rates of cardiometabolic disorders.
Limits
The abstract does not report the total participant sample size across the 15 studies. Included data reflect acute laboratory feeding protocols in healthy adults, limiting direct extrapolation to free-living chronic outcomes or individuals with metabolic disease. Insulin findings were inconsistent among studies not included in the numerical meta-analysis.
Cited by
- supports Eating the exact same meal and calorie amount in the morning produces a significantly lower insulin response than in the afternoon or evening because insulin sensitivity is highest in the morning.