Randomized Crossover Trial

C - Click here for explanation of classification scheme.

NEUTRAL: See Quality Criteria Checklist below.

To investigate whether repeated measurements of postabsorptive resting metabolic rate (RMR) and diet-induced thermogenesis (DIT) varied systematically with time of the day, i.e., between mornings and afternoons.

 

• Understand and give written consent
• Not on a special diet
• Not using any medication
• Non-smoker
• Healthy, as assessed by a medical questionnaire.

• Refusal to consent
• Not meeting inclusion criteria.

Recruitment

Not described.

Design

Randomized cross-over trial.

Statistical Analysis

• Analysis of variance and use of the model for a single-factor experiment with repeated measurements was used to test whether RMR and DIT varied systematically between mornings and afternoons
• Paired two-tailed Student's T-tests were used to evaluate differences in mean RMR, DIT and substrate oxidation rates between morning and afternoon sessions
• Confidence intervals were used to express mean differences in RMR, DIT and substrate oxidation rates between morning and afternoon sessions
• Pearson's product-moment correlation coefficients were used in correlation analyses.

Timing of Measurements

• Post-absorptive RMR was measured six times on different days in each subject: Three times in the morning and three times in the afternoon. There were more than two days between each session. Order was randomly assigned.
• All subjects completed the experiment in four weeks
• Morning RMR measured 12 hours to 14 hours post-absorptive
• Afternoon RMR measured six hours to seven hours post-absorptive.

Dependent Variables

Diurnal variation in post-absorptive RMR and DIT

• IC type: Ventilated hood
• Equipment of calibration: Yes
• Coefficient of variation using standard gases: No
• Rest before measure (state length of time rested, if available): 30 minutes
• Measurement length: Every 30 seconds and integrated over five-minute intervals
• Steady state: During measure, subjects watched video films. Subjects were instructed to minimize movements. O₂ consumption and CO₂ production were corrected for subjects' movements.
• Fasting length: 12 to 14 hours for morning measure, six to seven hours for afternoon measure
• Exercise restrictions prior to test: Yes
• Room temperature: 23°C to 25° C
• Number of measures within the measurement period: One
• Were some measures eliminated? No
• Were a set of measurements averaged? 30-second measures were taken each morning or afternoon for one hour, then averaged with a second set of measurements taken two days later
• If average, identify length of each measure and number of measurements: For post-prandial measures, O₂ and CO₂ measures were averaged per hour using five-minute interval data
• Coefficient of variation in subjects measures: No
• Training of measurer: Not specified
• Subject training of measuring process: Yes
• Monitored heart rate?
• Body temperature?
• Medications administered: Excluded
• Dietary: On morning of afternoon measurement, subjects were allowed a Dutch breakfast of approximately 480kcal (10% protein; 35% fat; 55% carbohydrate)
• Diet prior to DIT measurement: Yogurt-based liquid formula, approximately 456kcal (10% protein; 33% fat, 57% carbohydrate).

Independent Variables

Time of day: Morning vs. afternoon measurement of RMR and DIT.

• Initial N: Not given
• Final N: 10 white males
• Age: 21 years to 25 years (mean, 22±0.05 years SEM; range, 27 years to 34 years)
• Ethnicity: Not specified (perhaps Dutch)
• Other relevant demographics: None specified.

Anthropometrics

Men	Mean(±SEM)	Range
Weight (kg)	75.4±2.2	65.2-86.1
BMI (kg/m2)	22.3±0.6	19.5-25.9
FFM (kg)	64.0±1.7	5.39-71.3
Body fat percentage	15.1±1.2	7.8-19.3

Location

The Netherlands.

Indirect Calorimetry Results

• No significant day and time of day effect on RMR [F(1,10)=not given]. The 95% confidence interval for the average difference between mean morning and afternoon values in RMR is -0.02kcal per minute to +0.08kcal per minute. [Analyst note: When extrapolated to kcal per day, difference would range from -28kcal per day to 115kcal per day]. Mean morning and afternoon RMR values were used in subsequent analysis.
• Morning RMRs were significantly correlated with afternoon RMRs (R=0.95, P<0.01)
• RMRs and FFM were 25.9±0.6kcal per day per kilogram FFM in morning measures and 25.2±0.6kcal per day per kilogram FFM in afternoons
• The mean (±SEM) morning post-absorptive RMR in 10 subjects was 1.15±0.04kcal per minute (range, 0.98±0.05kcal per minute to 1.40±0.06kcal per minute)
• The mean (±SEM) afternoon post-absorptive RMR was 1.12kcal±0.03kcal per minute (range, 1.0±0.01kcal per minute to 1.3±0.02kcal per minute). 

Diet-Induced Thermogenesis

Analysis of variance showed no significant effect of day and time of day on total DIT. Therefore, each person’s mean morning and afternoon DIT values were used in subsequent analyses.

The 95% CI for mean difference between morning and afternoon DIT values was -1.8% to +2.6% of the energy content of the test meal, i.e., -8.1kcal to +12.0kcal. Mean morning DIT values were significantly correlated with mean afternoon DIT values (R=0.89, P<0.01).

Diet-Induced Thermogenesis in Subjects After Ingestion of a Meal on Different Times of the Day

	Percentage of Energy Content of Meal
	Morning (mean±SEM)	Afternoon (mean±SEM)	Total (mean±SEM)
1	7.5±0.6	5.2±1.5	6.6±1.0
2	6.9±1.3	13.6±6.3	10.2±1.6
3	7.8±0.7	4.8±1.3	6.3±1.0
4	9.3±4.5	9.8±1.2	9.5±1.9
5	6.1±0.5	6.4±2.8	6.2±1.2
6	6.3±1.4	4.7±1.08	5.5±0.9
7	5.2±0.9	7.6±3.4	6.4±1.6
8	6.3±0.3	5.4±0.5	5.8±0.4
9	7.0±0.8	4.6±1.2	5.8±0.9
10	10.2±0.0	6.8±1.6	8.5±1.2

The coefficient of variation for energy intake was approximately 0.5%.

The mean±SEM percentage of diet-induced thermogenesis was 7.4%±0.05% and 6.9%±0.9% for morning and afternoon measures, respectively. Overall, the mean±SEM percentage of diet-induced thermogenesis for all measures (mean of four measurements) was 7.1%±0.5%.

Diet-Induced Thermogenesis
(kcal per minute)

• No significant effect of time of day on the mean hourly DIT values was observed
• On average, DIT was slightly higher on morning sessions in the first hour after ingestion of the meal, in comparison with afternoon sessions
• In contrast, DIT was higher in the third and fourth hour in the afternoon sessions after ingestion of the meal, in comparison with afternoon sessions
• The mean DIT in the fourth hour after ingestion of the test meal was approximately 0.02kcal per minute (2% to 3%) above the corresponding post-absorptive RMR on morning sessions and approximately 0.05kcal per minute (4% to 5%) more than the corresponding post-absorptive RMR on afternoon sessions.

Substrate Oxidation

• RQs were significantly higher on mornings in the first hour after ingestion of the meal, in comparison with afternoon RQs. The reverse was true for the third and fourth hour after ingestion of the test meal.
• Carbohydrate oxidation was significantly higher and fat oxidation significantly lower in the mornings the first hour after ingestion of the test meal than in the afternoons
• During the third and fourth hour post-prandially, carbohydrate oxidation was lower in the morning in comparison with the afternoon, in contrast to fat oxidation.

Mean Carbohydrate and Fat Oxidation in Absolute Amounts and as a Percentage of Total Energy Expenditure in Subjects Before and After Ingestion of a Meal at Different Times of the Day^a

Oxidation During	Carbohydratesb		Fats
	Morning	Afternoon	Morning	Afternoon
RMR, % kcal/min (mg/min)	39 (117)	39 (115)	40 (50)	40 (47)
PEE 1, % kcal/min (mg/min)	64 (234)	57* (196*)	16 (24)	24* (33)
PEE 2, % kcal/min (mg/min)	66 (241)	66 (226)	14 (21)	14 (20)
PEE 3, % kcal/min (mg/min)	46 (152)	54* (177)	33 (46)	25* (34*)
PEE 4, % kcal/min (mg/min)	27 (84)	37* (133*)	51 (65)	42* (53)
PEE t, % kcal/min (mg/min)	52 (178)	54 (178)	28 (39)	26 (35)

a: RMR, post-absorptive resting metabolic rate; PEE, post-prandial energy expenditure (PEE 1 during first hour, PEE 2 during second hour; PEE 3 during third hour; PEE 4 during fourth hour and PEE t, during total post-prandial periods)
b: Expressed on a glucose basis
*Significantly different from morning values, P<0.05

• Protein oxidation was not significantly different between morning tests and afternoon tests: 57±3mg per minute vs. 53±3mg per minute.

Energy and Nutrient Balances

• No significant differences observed between morning and afternoon tests in total oxidation and storage or balance of the various nutrients
• On average, energy balance, i.e., energy retention, was slightly higher in afternoon than in morning sessions (mean difference in energy retention 95% CI, -0.02kcal to +31.8kcal)
• On average, less than 3% of ingested carbohydrates was converted to fat.

As stated by the author in body of report:

• "In our study, there were no significant diurnal variation in postabsorptive RMR and DIT."
• "The possibility that morning measurements would have a residual effect on afternoon assessments of energy expenditure was excluded d/t morning and afternoon measurements were performed on different days... [therefore] the normal intraindividual, between-day variation in morning and afternoon RMR and DIT was allowed"
• "In the present study, the subjects had a shorter duration of the fast on the afternoon tests than on the morning tests... this may have confounded the afternoon measurements of postabsorptive RMR."
• "Second part of the study measures systematic variation with time of the day in the response to energy metabolism to food. The time of day did not significantly influence DIT... similar to findings for RMR, this was not due to great interindividual variability in difference I DIT between morning and afternoon tests. Mean DIT had decreased almost to 0 in the fourth hour after ingestion of the meal both in the morning and in the afternoon."
• "Time of day had no significant effect on postabsorptive RMRM or DIT.  No systematic diurnal variation was observed in total preprandial and postprandial substrate oxidation."
• "Hourly postprandial substrate oxidation indicated an icreased glucose oxidation in subjects in a more prolonged fasting state."

University/Hospital:

Wageningen Agriculture Netherlands

Strengths

• Well-planned research design to control for residual effects of morning assessments on the afternoon measure
• Systematically explained IC measure.

Generalizability/Weaknesses

• Questionable validity of indirect calorimeter
• "Generalizable to nonobese young adult males and effects of high fat or high CHO diet consumption"
• These important variables on REE measurement accuracy did not clearly define steady state, however researchers stated they "adjusted for movements." Subjects watched movies during measure and thus definition of RMR (i.e., limited brain activity) may not have been accomplished. Gave a “yes” for IC measure quality due to repeat measures and aggressive adherence to measurement protocol.