Insulin Secretion follows a circadian rhythm. It is lowest in the morning and peaks in the evening!
See the following articles
First Article:
Am J Physiol. 1996 Aug;271(2 Pt 1):E246-52. https://www.ncbi.nlm.nih.gov/pubmed/8770017
Evidence for a circadian rhythm of insulin secretion.
Author: Boden G1, Ruiz J, Urbain JL, Chen X.
Abstract
“Insulin secretion was studied in healthy volunteers at three different levels of glycemia. Plasma glucose was clamped at approximately 5, approximately 8.8 and approximately 12.6 mM for 68 h. Measured were serum insulin concentration and insulin secretion rates (ISR), the latter by deconvolution of plasma C-peptide concentration. Rhythmic patterns of ISR were identified (with a refined first-order Fourier transform) at all three glucose concentrations tested but were most clearly seen at 12.6 mM. ISR and serum insulin concentration changed in a circadian (approximately 24 h) rhythm, increasing from a nadir between midnight and 6 A.M. and reaching a peak between noon and 6 P.M. At 12.6 mM hyperglycemia, the amplitude of the insulin concentration cycles was greater than that of the ISR cycles (+/- 13.0 vs. +/- 8.7%) due to a decrease in insulin clearance (from 1.55 to 0.5 l/min, P < 0.01). Plasma melatonin levels (a marker of light-dark rhythmicity) changed in the opposite direction, i.e., they peaked when ISR bottomed and bottomed when ISR peaked. We concluded that normal human subjects have a circadian rhythm of insulin secretion, which becomes more apparent with rising ISR, and that circadian changes in ISR, rising during the day and falling during the night, may be one explanation for the well-established observation that glucose tolerance and insulin responses to glucose and meals are higher in the morning than at night.”
Second Article:
Int J Obes (Lond). 2015 Dec;39(12):1689-95. https://www.ncbi.nlm.nih.gov/pubmed/26219416
Is the timing of caloric intake associated with variation in diet-induced thermogenesis and in the metabolic pattern? A randomized cross-over study.
“Abstract
BACKGROUND/OBJECTIVES:
Food-induced thermogenesis is generally reported to be higher in the morning, although contrasting results exist because of differences in experimental settings related to the preceding fasting, exercise, sleeping and dieting. To definitively answer to this issue, we compared the calorimetric and metabolic responses to identical meals consumed at 0800 hours and at 2000 hours by healthy volunteers, after standardized diet, physical activity, duration of fast and resting.
SUBJECTS/METHODS:
Twenty subjects (age range 20-35 years, body mass index=19-26 kg m(-)(2)) were enrolled to a randomized cross-over trial. They randomly received the same standard meal in the morning and, 7 days after, in the evening, or vice versa. A 30-min basal calorimetry was performed; a further 60-min calorimetry was done 120-min after the beginning of the meal. Blood samples were drawn every 30-min for 180-min. General linear models, adjusted for period and carry-over, were used to evaluate the ‘morning effect’, that is, the difference of morning delta (after-meal minus fasting values) minus evening delta (after-meal minus fasting values) of the variables.
RESULTS:
Fasting resting metabolic rate (RMR) did not change from morning to evening; after-meal RMR values were significantly higher after the morning meal (1916; 95% confidence interval (CI)=1792, 2041 vs 1756; 1648, 1863 kcal; P<0.001). RMR was significantly increased after the morning meal (90.5; 95% CI=40.4, 140.6 kcal; P<0.001), whereas differences in areas-under-the-curve for glucose (-1800; -2564,-1036 mg dl(-1) × h, P<0.001), log-insulin (-0.19; -0.30,-0.07 μU ml(-1) × h; P=0.001) and fatty free acid concentrations (-16.1;-30.0,-2.09 mmol l(-1) × h; P=0.024) were significantly lower. Delayed and larger increases in glucose and insulin concentrations were found after the evening meals.
CONCLUSIONS:
The same meal consumed in the evening determined a lower RMR, and increased glycemic/insulinemic responses, suggesting circadian variations in the energy expenditure and metabolic pattern of healthy individuals. The timing of meals should probably be considered when nutritional recommendations are given.”