AWM: Eating Frequency and Patterns (2013)


Gluck ME, Venti CA, Salbe AD, Krakoff J. Nighttime eating: Commonly observed and related to weight gain in an inpatient food intake study. Am J Clin Nutr. 2008; 88(4): 900-905.

PubMed ID: 18842774
Study Design:
Retrospective Cohort Study
B - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

To retrospectively assess the prevalence of nighttime eating in a population of Pima Indian and white adults who had previously participated in a carefully controlled inpatient study of food intake and to relate the effect of nighttime eating to overall calorie consumption and subsequent weight gain.

Inclusion Criteria:
  • Pima Indian and white adults who had previously participated in a controlled inpatient study of food intake
  • None were diabetic, according to the criteria of the WHO.
Exclusion Criteria:

Pima Indian and white adults who had not participated in the previous food intake study.

Description of Study Protocol:


  • 117 Pima Indians from the Gila River Indian Community 
  • 43 whites by advertisement from the Greater Phoenix area.


Retrospective cohort study.

Blinding Used

Implied with measurements.


Healthy non-diabetic Pima Indians and whites were admitted to a clinical research unit. After consuming a standardized diet for three days, participants ate ad libitum from a computer-operated vending machine that recorded the time and energy intake of food selections. Energy intake was calculated as mean kcal per day. Follow-up weights were available for 94 of these volunteers. 

Statistical Analysis

All procedures were carried out with SAS software (version 8.2; SAS Institute, Cary, NC). Pearson's correlation coefficients, the chi-square test and linear regression models were used to test for significance in relationships. Statistical significance was set at less than 0.05.


Data Collection Summary:

Timing of Measurements

  • During the final three days on the metabolic ward, subjects self-selected all food by using a computer-operated vending machine system
  • Subjects had free access to the vending machines 23.5 hours per day
  • Follow-up weights were obtained for 94 of the volunteers at six or more months after their baseline weights had been obtained for the initial metabolic study.

Dependent Variables

  • Weight (kg)
  • Body fat (%)
  • BMI (kg/m²).

Independent Variables

Nighttime mean energy intake (kcal).

Description of Actual Data Sample:
  • Initial N: 117 Pima Indians (67 males, 50 females) and 43 whites (29 males, 13 females)
  • Attrition (final N): 94 subjects had follow-up weights (87 Pima Indians and seven whites)
  • Age: 34±8 years 
  • Ethnicity: American Indians and whites
  • Anthropometrics: Weight, body fat, BMI, cholesterol, protein and fat intake (as percent of kcal) did not differ between non-nighttime eaters and nighttime eaters
  • Location: Phoenix, AZ.
Summary of Results:

Key Findings

  • 55 subjects (36%) were nighttime eaters (NEs; persons who ate between 11:00 p.m. and 5:00 a.m. on one of the three days)
  • Prevalence was similar among whites and Pima Indians (37% and 35%, respectively)
  • There were no significant differences in body mass index or percentage body fat between NEs and non-NEs
  • NEs consumed more calories per day (4,758) than did non-NEs (4,244; P=0.02), but
    the percentage of calories from macronutrients did not differ. NEs consumed approximately 15% (690kcal) of their daily energy during nighttime episodes
  • After control for baseline weight and follow-up time, NEs (N=29) gained more weight (6.2kg) than did non-NEs (N=65; 1.7kg; P=0.03).


Author Conclusion:
  • Nighttime eating was common in this controlled inpatient study of food intake and it did not vary in prevalence between Pima Indians and whites. Nighttime eaters (NE) consumed more total calories than did non-nighttime eaters (non-NE) and the difference in intake resulted from the calories ingested at night. 
  • Although the groups did not differ by either BMI or percentage of body fat at baseline, NEs gained significantly more weight during the follow-up period that did the non-NEs
  • Compared to previous studies a strength of this study was that subjects had ad libitum access to food for nearly 24 hours per day on three consecutive days and follow-up data were available for subjects (unlike either of two earlier studies referenced in the article)
  • Our findings show an association between altered sleep patterns and greater adiposity, which suggests that the identification and avoidance of nighttime eating could be a strategy for preventing weight gain.   
Funding Source:
Government: National Insitiutes of Health
Reviewer Comments:

Other similarities and differences between Pima Indians and white adults are not described. Follow-up sample may not be as representative as original sample.

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? ???
  2.4. Were the subjects/patients a representative sample of the relevant population? ???
3. Were study groups comparable? ???
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  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? ???
  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? ???
  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%.) ???
  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? Yes
  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.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? Yes
  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? 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? Yes
  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)? Yes
  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? 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