BF: Dietary Factors, Breast Milk and Infant Outcomes (2008)


Motil KJ, Montandon CM, Hachey DL, Boutton TW, Klein PD, Garza C.  Relationships among lactation performance, maternal diet, and body protein metabolism in humans. Eur J Clin Nutr. 1989; 43: 681-691. 

PubMed ID: 2612458
Study Design:
Before-After Study
D - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:

To quantify milk volume and composition in women across a range of lactation stages; to determine the relationships among milk production, stage of lactation, maternal diet and body protein metabolism.

Inclusion Criteria:

Lactating women whose duration of lactation was 1.5 months±0.2 months, 5.4 months±0.8 months or 12.2 months±0.6 months.

Exclusion Criteria:

Not reported.

Description of Study Protocol:


Not reported.


Before and after study (three groups of differing lactation durations).


All women received controlled, constant diets providing average protein intakes of 1.5g per kg per day and energy intakes simulating usual patterns.

Statistical Analysis

  • ANOVA to determine differences in maternal milk production and composition among the three groups
  • Multiple regression to determine relationships between dependent variables (milk production and composition) and the independent variables (protein, energy intakes, components of body protein metabolism and time postpartum).


Data Collection Summary:

Timing of Measurements

  • Pre-study: Medical history obtained and examination performed
  • Initial data collection outside of lab: At-home, three-day food record, followed by controlled constant diet provided for seven days
  • Data collection in-lab
    • During last four days of dietary period, subjects admitted to lab for nitrogen (N)-balance measurements
    • Milk production measured at home for three days before admittance to lab and throughout balance period
    • 24-hour milk sample obtained on last day of balance period for analysis of composition
    • On day seven of controlled diet, whole-body protein turnover studies performed. 

Dependent Variables

  • Milk production (test-weighing of infants; manual/mechanical pumping; milk consumed by infant; milk expressed by mother)
  • Milk composition (from entire contents of alternate breasts for 24 hours): N and non-protein N (automated microKjeldahl method); energy (adiabatic bomb calorimetry).

Independent Variables

  • Protein and energy intakes
    • Food intake over 72 hours measured and recorded by each subject throughout three consecutive days, including one weekend day
    • Usual intakes calculated from these records
    • All women then received controlled, constant diet providing average protein intakes of 1.5g per kg per day and energy intakes simulating usual patterns. 
  • Components of body protein metabolism
    • N-balance (N of food, milk, urine, feces+assumed unmeasured N losses of five mg per kg per day)
    • Amino acid kinetic studies (infusion of isotopically labeled amino acids, flux measured).
  • Time postpartum.

Control Variables

  • Controlled dietary intake
  • Timing of measurements.
Description of Actual Data Sample:


Initial N: 12

Attrition (final N): 12 (four per lactation-duration group)

Age: 28.0 years±3.3 years

Ethnicity: Not reported

Other relevant demographics: Not reported

Anthropometrics: 166.4cm±8.1cm; 63.0kg±11.6kg

Location: Houston, TX.


Summary of Results:

Results presented here focus on total cohort of 12 women.

Milk production was similar among the women during the three-day periods of measurement in their homes and in the lab. Milk production was highest at five months postpartum, although the differences in milk production over time were not significant.

Milk total N and protein outputs and concentrations decreased significantly with increasing time postpartum. 

No significant relationships were noted between milk energy outputs and concentrations and time postpartum. No significant relationships between milk production and milk N and energy concentrations. 

Milk production showed significant positive relationships with N and energy intakes; adjustment for time postpartum strengthened the relationship between N intakes, but not energy intakes and milk production (P<0.02, r=0.66). No significant relationships between milk N or energy concentrations and maternal diet. 

Milk total N and protein: N concentrations associated negatively with N balance after adjusting for time postpartum (P<0.05, r=0.77). There was a significant positive relationship between milk production (but not milk N or energy concentrations) and maternal body protein metabolism, and this relationship was not dependent on time postpartum (P<0.01, r=0.73).



Author Conclusion:

There are associations among lactation performance, maternal diet and metabolic responses of body protein stores in well-nourished women. 

Strategies such as provision of nutritional support to the nursing mother are warranted for the improvement of milk production in settings where nutrient insufficiency and malnutrition prevail.

Funding Source:
Government: NIH, USDA
Reviewer Comments:
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? No
  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? No
  2.2. Were criteria applied equally to all study groups? ???
  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? ???
  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? ???
  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? Yes
  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%.) N/A
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? N/A
  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? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? Yes
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? ???
  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