Diurnal postprandial responses to low and high glycaemic index mixed meals.
Level 2 - randomized trial
Individual randomized crossover trial
PubMed 24135087 · doi:10.1016/j.clnu.2013.09.018
What was done
Ten healthy participants completed a randomized controlled crossover study after a standardized premeal and an 8-hour fast. Participants consumed macronutrient- and calorie-matched mixed meals with either a low glycemic index (GI 37) or high glycemic index (GI 73) at two different times of day: morning (08:00 h) and evening (20:00 h). Blood samples were collected for 2 hours postprandially to measure glucose area under the curve (AUC) and insulin responses.
What was found
Postprandial glucose AUC was significantly higher in the evening than in the morning after both the low-GI meal (p < 0.001) and the high-GI meal (p = 0.003). There was a trend (p = 0.06) toward a higher glycemic response in the evening for the low-GI meal. In the morning, little difference was observed between low- and high-GI meals. No differences were observed in insulin responses. Absolute values and effect sizes were not reported in the abstract.
Why it matters
Standard GI testing conducted in the morning may not accurately reflect glycemic impact across the full diurnal cycle, as metabolic handling of low-GI meals is less effective in the evening.
Limits
The sample size was very small (n = 10) and restricted to healthy individuals. The monitoring window was short (2 hours postprandially), and the abstract omitted absolute numerical values for glucose AUC and insulin concentrations.
Cited by
- supports Postprandial glucose response is significantly higher in the evening compared to the morning, and humans are more insulin sensitive in the morning.