AWM: Eating Frequency and Patterns (2013)

Study Design:
- Click here for explanation of classification scheme.
Quality Rating:
Research Purpose:

To determine whether altered meal timing patterns affected:

1) weight and body composition changes during a weight loss intervention that combined regular exercise with a controlled, moderately energy restricted diet , and

2) energy utilization under standardized conditions of rest, exercise, following meals and following exercise to determine whether altering meal patterns would affect the metabolic fate of energy-yielding nutrients.

Inclusion Criteria:
  • women
  • 20-40 years of age
  • healthy
  • premenopausal with normal menstrual cycles
  • body fat > 30%
Exclusion Criteria:
  • self-reported tobacco use
  • positive urine test for nicotine, narcotics, or mood-altering drugs
  • history of orthopedic injury
  • medical contraindication for partipation in the exercise program
Description of Study Protocol:

Recruitment Not specified        

Design 15- week metabolic unit study, consisting of a 3-week stabilization period for weight maintenance, followed by 2 consecutive 6-week experimental periods for weight loss. The macronutrient composition of the intake was kept constant throughout the study at 60% carbohydrate, 18% protein, and 22% fat. Energy intake restriction and exercise was used for weight  loss.  Each subject was assigned to one of 2 groups such that mean values for body weight and composition, physical fitness, and history of dietary restraint were similar between groups. For the 1st experimental period, group A ingested 70% of the daily energy intake in the AM and group B ingested 70% of their energy intake in the PM. For both conditions, the 70% was broken down into 4 meals - the AM with 35% at breakfast, 35% at lunch, 15% at dinner and 15% at evening snack, with the PM being 15% at breakfast, 15% at lunch, 35% at dinner, and 35% at evening snack. The mean energy intake was 107 ±6 kJ/kg.  For the 2nd experimental period, the groups switched to the alternate energy intake pattern.  For both groups, the time of the exercise sessions remained constant through both experimental periods.

Blinding used (if applicable) Not used.

Intervention (if applicable) Energy intake was individually prescribed to be 2 MJ/day below stabilization energy intake.  Exercise involved aerobic activity and weight training and was individualized depending on the subjects' ability and VO2max. Subjects lived on the metabolic ward during study.

Statistical Analysis ANOVA was used to test the effects of order, meal pattern, and period on change in weight and body composition and energy utilization.  If a significant order effect was found, the meal pattern effect was examined for each period using Student's t test.  Probability was set at < 0.05.

Data Collection Summary:

Timing of Measurements  Dietary intake was measured daily, subjects were weighed daily, body composition was determined twice weekly, and energy expenditure and utilization was measured using 2 protocols, one conducted twice during the last 2 weeks of both experimental periods, and one conducted twice during weeks 2-4 of each experiemental period.

Dependent Variables  For each 6 week experimental period: weight loss, fat-free mass loss,% fat; also energy expenditure and utilization.

Independent Variables meal pattern assignment

Control Variables none mentioned

Description of Actual Data Sample:

Initial N: 12 females    

Attrition (final N): 10 females

Age: group A mean = 29.8 ± 7.6 years, group B mean = 29.2 ±4.2 years.

Ethnicity: 8 Caucasian, 1 Asian, 1 Black

Other relevant demographics: No other demographics included

Anthropometrics  weight, height, FFM, body fat, RMR, and RER prior to weight loss are reported - although means are close, it does not appear they were tested for between group differences.

Location: Western Human Nutrition Research Center at UC-Davis

Summary of Results:

Effect of AM pattern vs. PM pattern on changes in weight and body composition during weight reduction
AM pattern PM pattern
Weight, kg/6 wk -3.90 ± 0.19 -3.27±0.26**
Fat-free mass, kg/6 wk -1.28± 0.14 -0.25±0.16*
Fat percentage, %/6 wk -1.83±0.22 -2.52±0.29***

*P<0.001, **P<0.01, ***P<0.05


Effect of AM pattern vs. PM pattern on changes in fat mass and body energy stores during the first 6 wk of weight loss (period 1) and the second 6 wk of weight loss (period 2)
AM pattern PM pattern
Fat mass, kg/6 wk
    Period 1 -2.91±0.08 -3.69±0.15*
    Period 2 -2.57±0.28 -2.02±0.20
Energy content, MJ/6 wk
    Period 1                 -116.7±3.6 -144.0±6.0*
    Period 2 -105.0±10.8 -80.4±8.1


  • Large AM meals resulted in greater loss of weight and FFM compared to large PM meals (p < 0.01 and < 0.001, respectively).
  • Large PM meal pattern resulted in a greater decrement in body fat % (p < 0.05).
  • Significantly greater loss of fat mass with the PM pattern in period 1, but not 2.
  • More body energy stores were lost with the PM pattern during period 1 (p < 0.05), but not 2.
  • The effects on energy expenditure and utilization with each pattern were as expected.
  • Meal pattern did not affect AM RMR, pre-exercise, exercise, or post-exercise metabolic rate.


Author Conclusion:

While weight loss was greater with the AM large meal pattern, there was greater loss of FFM with this pattern.  The authors suggest that this may be due to the lack of precision in their method for measuring body composition which was not able to quantify the specific components of FFM, but conclude that their results suggest that large PM meals may be effective in maintaining FFM. They also conclude that they found little evidence of consistent changes in energy utilization associated with meal pattern and that period effects may be due to greater weight loss during initial weight loss efforts.

Funding Source:
Government: USDA
Reviewer Comments:
This was a sophisticated, well-designed study. Inclusionary and exclusionary criteria ensured a homogeneous sample, eliminating many factors that might have affected results.  The cross-over design provides a more stable estimate of true effects and the authors provide a thoughtful discussion of their findings and future research questions.
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? Yes
  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? Yes
  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? No
  4.1. Were follow-up methods described and the same for all groups? N/A
  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? ???
  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? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? Yes
  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? Yes
  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? No
  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? Yes
  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