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AWM: Eating Frequency and Patterns (2006)

Citation:
 
Study Design:
Class:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:
To study the relationship between the amounts eaten at various times of the day and the total amount eaten over the course of the entire day.
Inclusion Criteria:
None stated.
Exclusion Criteria:
Actively dieting, pregnant or lactating, on chronic medication, or alcoholic.
Description of Study Protocol:

Recruitment Data used for this study was gathered in previous studies and re-analyzed.  Readers are referred to earlier publications for details, such as recruitment.

Design  Data from previous studies was used for the current analyses.  Subjects were recruited for a study about intake control in humans but were unaware that the time of day and intake were being studied. Weight and height were measured.  Participants were trained and given a pocket-sized diary to record intake for 7 days.  2 individuals who ate with the participant were contacted and asked to verify the reported intake. In no cases did these individuals contradict either the nature or the amount reported.  Total and meal amounts of nutrients ingested during the following time periods were calculated:  0600-0959, 1000-1359, 1400-1759, 1800-2159, and 2200-0159 h. % of total daily intake of each nutrient ingested during each period, and energy density (MJ/g) were calculated.  A 2nd energy density was calculated excluding drinks. Food diaries with a reported intake         < 110% of their estimated BMR were excluded for some of the analyses.

Blinding used (if applicable) NA

Intervention (if applicable) NA

Statistical Analysis  Correlations, t-tests,  and repeated measures ANOVA with a Bonferroni correction for multiple comparisons for the t-tests.

Data Collection Summary:

Timing of Measurements Over 7 days

Dependent Variables total intake

Independent Variables

intake during 5 periods of the day - recorded on a pocket diary;for a reported intake to be classified as an individual meal, it had to contain at least 209 kJ (49.9 kcals), and be separated in time for the preceding and following intakes by 45 minutes. (Note: other amounts and time intervals were explored and no differences were found). 

For each identified meal:

  • the meal size of food energy
  • CHO
  • fat
  • protein
  • alcohol
  • duration of the meal
  • rate of intake
  • duration of the intervals prior to and after the meal
  • the duration of the after meal interval divided by the meal size (satiety ratio)
  • time
  • number of other people eating with them 
  • self-rating of hunger
  • thirst
  • anxiety
  • depression
  • the attractiveness of the food

Control Variables  none stated

Note:  analyses were extensive and complicated and, for some analyses, intake during the 5 periods was also used as the dependent variable.

Description of Actual Data Sample:

Initial N: 867 (375 men and 492 women)

Attrition (final N): 586 subjects (gender breakdown not reported) had reported intake > 110% of BMR.  While the authors report that correlations done with this sub-group did not differ from the larger group, it is unclear if all analyses reported are done with the 867.  N is reported on some, but not all, figures and tables.

Age: 36.3 +/- 13.8 years

Ethnicity: not reported

Other relevant demographics: none reported

Anthropometrics BMI=24.5 +/- 4.3 (not reported separately for men and women)

Location: Atlanta

Summary of Results:

Time Periods:  

  • 1st = 0600-0959
  • 2nd= 1000-1359
  • 3rd = 1400-1759
  • 4th = 1800-2159
  • 5th = 2200-0159

Results:

  • Total food energy differed among the 5 time periods (F=832.4, P<0.01]) with peaks during the 2nd and 4th periods.
  • Energy density of overall intake differed over the 5 time periods (F=21.1, P<0.01) due  to the 1st period being significantly less dense than all other periods.
  • When energy density was calculated without beverages, there was a significant change over the day (F=40.0, P<0.01) with density during 1st period  being signficantly greater than the 2nd, 3rd, and 4th and density during the 5th period being greater than all other periods.
  • Mean meal sizes of food energy differed among  the periods (F=131.0, P<0.01) with meal sizes during all periods different from all other periods except that the 2nd period did not differ from the 3rd.
  • Meal size differences for macronutrients were the same as food energy except that the meal sizes for both fat and alcohol differed from all other periods.
  • The changes in meal size occurred due to an increase in the time spent eating (F=17.6, P<0.01), and not to the rate of intake (F=0.3, P>0.50).
  • Although meal size increased over the day up until the 5th period, the meal interval decreased over the same period (F=390.0,  P<0.01).
  • Satiety ratios decreased over the day (F=144.3, P<0.01); during the 1st period they were higher than the other 4 periods, and periods 2 and 3 were higher than periods 4 and 5.
  • Correlations between the proportions of food energy ingested during each time period and total energy ingested during the day were negative (and mostly significant) during the 1st 2 periods and were positive (and mostly significant) during the last 3 periods of the day. When the correlations were conducted using only the 586 who met the criterion for adequate reporting, the same pattern emerged. When weekend days and weekdays were analyzed separately, the pattern was the same.
  • Dietary energy density during the 5 time periods was significantly positively correlated with total daily intake, regardless of time period and whether density was calculated with or without the inclusion of drinks.
  • When data was re-analyzed by dividing individual days into whether or not intake for the morning, afternoon, and evening periods were above or below that individual's mean proportional intake for that period, an interaction (F=27.76, P<0.01) was seen such that, when intake was below the mean for the morning,  the participants ate more over the entire day than they did on days when they were above the mean.  Additionally,  on days when the proportion of intake was below the mean for the evening, the participants ate significantly less over the entire day than they did on days they they were above the mean.
  • When analyses were repeated with each macronutrient as the DV, there was an interaction for both fat (F=19.24, P<0.01) and protein (F=32.99, P<0.01) such that, on days when intake in the morning was higher than the mean, participants ate less total fat and protein than on days when they ate less than the mean, and on days when intake in the evening was higher than the mean, the participants ate more total protein than on days when they ate less than the mean.
  • There were no significant differences between the below and above the mean days for meal frequency, the number of people present, and the hunger and palatability ratings.
Author Conclusion:
The present study found that intake by free-living humans varies considerably over the day.  The amount of energy ingested appears to increase over the day with peaks during the lunch and dinner periods.  This is not due to an increase in energy density, except possibly late at night, but occurs as a result of increasingly larger meals of longer duration over the day.  Also, the larger meal sizes over the day were accompanied by smaller amounts of time elapsing before the next meal, producing a precipitous decline in the satiety ratio.  Hence, over the day, intake increases, but the satiating effect of intake decreases.  In essence, the present analysis suggests that intake in the morning of low density foods is satiating and can reduce the amount ingested over the rest of the day to such an extent that the total amount ingested for the day is less.  It also suggests that low density intake during any portion of the day could reduce overall intake.  Finally, it suggests that intake in the late night time period may supplement the earlier intake to the extent that it results in greater overall daily intake.
Funding Source:
University/Hospital: Georgia State University
Reviewer Comments:

This is a well-done study with extremely complicated analyses.  The author has managed to dissect the effects of intake throughout the day and relate them to total energy intake, as well as determine the effect of the social context of the meals and and the hunger of the participants.

The finding that intake earlier in the day is more satiating and that more intake earlier in the day leads to a lower total intake provides an excellent strategy for decreasing overall intake and, although this was not a focus of the study, appears to provide additional support to the finding that eating breakfast (and particularly high fiber breakfasts) is associated with lower BMIs.  Additionally, the finding that intake during the late evening increases overall intake lends support to recommendations that evening intake be minimized. The fact that these finding held up within individual participatns further strengthens them.

Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? ???
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? N/A
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? N/A
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) N/A
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? Yes
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
5. Was blinding used to prevent introduction of bias? N/A
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) N/A
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? N/A
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? N/A
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? N/A
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes