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


Strode MA, Dewey KG, Lonnerdal B. Effects of short-term caloric restriction on lactational performance of well-nourished women. Acta Paediatr Scand. 1986; 75: 222-229.

PubMed ID: 3754376
Study Design:
Non-randomized crossover trial
C - Click here for explanation of classification scheme.
Quality Rating:
Negative NEGATIVE: See Quality Criteria Checklist below.
Research Purpose:

To determine the effects of caloric restriction among well-nourished lactating women on milk volume, composition and plasma prolactin levels.

Inclusion Criteria:

Women six to 24 weeks postpartum, exclusively breastfeeding, who gained at least 11kg during pregnancy. 

Exclusion Criteria:

Not reported.

Description of Study Protocol:


One-week non-randomized trial; subjects given the choice to be included in experimental or control group.


One-week self-selected assignment to one to two groups:

  • Experimental group: 20% to 30% reduction of caloric intake, while maintaining usual dietary pattern and proportion of kcal from protein, fat and carbohydrates
  • Control group: No reduction in kcal intake; maintaining usual dietary pattern.

Statistical Analysis

 Planned statistical tests not reported in Methods.

Data Collection Summary:

Timing of Measurements

  • Pre-trial: Height, pre-gravid weight and gestational weight gain recorded; subject given a choice between Experimental and Control groups.
  • First week, baseline: Infant weight and length measured and recorded at beginning and end of week; completion of seven-day weighed diet record; collection of two breast milk samples (hand pump); two-hour to 24-hour records of infant's milk consumption (test-weighing); daily record of mom's own self-weight; pre-nursing blood sample drawn at end of week for prolactin analysis. 
  • Second week, Trial One: All baseline measures repeated, with experimental group reducing kcal intake by 20% to 30%. Experimental group instructed to collect breast milk samples and complete infant test-weighings close to the end of the week. 
  • Third week: Experimental group returns to normal kcal intake (restriction removed); dietary intake not recorded, subjects advised to discontinue weight loss. Experimental group instructed to collect breast milk samples and complete infant test-weighings close to end of week. No plasma samples collected during week three.

Dependent Variables

  • Maternal energy and nutrient intake (two-day to seven-day records; nutrient analysis program)
  • Breast milk volume: Measured by infant breast milk intake (two 24-hour records of her infant's milk consumption by test-weighting, using a pediatric beam balance)
  • Breast milk nutrient composition: hand-pumped samples
  • Protein concentration of milk (modified Lowry method)
  • Fat content of milk (calorimetric phosphovanillin assay)
  • lactose content of milk (spectrophotometrically, B-galactosidas and glucose oxidase assay)
  • Energy content of milk (heats of combustion, pro 5.65kcal per g; fat 9.25kcal per g; CHO 3.95kcal per g)
  • Plasma prolactin (radioimmunoassay, liquid phase double-antibody system).

Independent Variables

Experimental group (one week kcal restriction) vs. Control group  (no restriction).

Control Variables

Duration of trial, timing of measurements.

Description of Actual Data Sample:
  • Initial N: 22
  • Attrition (Final N): 22

  Experimental Group (N=14) Control Group (N=8)
Maternal Age (Years)
Height (cm)
Pre-Pregnancy Weight (kg)
Percentage Ideal Pre-Pregnancy Weight
GWG (kg)
Week One, Study Weight (kg)
Percentage Ideal Weight, Week One
Infant Birth Weight per Age Percentile
Infant Age, Week One
Infant Sex 7 males, 7 females 6 males, 2 females

  • Ethnicity: Not reported.
  • Location: Dept of Nutrition, University of California, Davis, CA, USA.
Summary of Results:


Experimental (N=14)

Control (N=8)

Statistical Significance of Group Difference

24-Hour Infant Milk Intake (g)

Week One



 *P=0.06 from Week One

Week Two 718±150 671±114
Week Three 684±155 (N=13)* 702±101
Feedings per Day (N)

Week One



 *P<0.05 from Week One

Week Two 6.8±2.0 7.1±1.8
Week Three 6.1±1.5 (N=13)* 7.1±1.8
Infant Weight Gain (gain per day)

Week One

21.3±10.2 (N=13)


 *P=0.054 from Week One

Week Two 17.6±9.6 12.2±9.6
Week Three 13.6±9.4 (N=13)* 15.9±8.2 (N=7)
Plasma Prolactin (ng per ml)

Week One

29.3±11.0 (N=9)

33.7±12.1 (N=7)

Week Two 30.1±12.3 (N=9) 26.6±3.9 (N=7)

When controlling for maternal percent of ideal weight, marginally significant correlations were found in group E between week two caloric intake as a percentage of that in week one (caloric intake ratio 2:1) and change in milk intake, both from week one to week two (R=0.453, P=0.06) and from week one to week three (R=0.484, P=0.056). A greater decrease in caloric intake was associated with a decrease in infant milk intake. Likewise, a lower absolute caloric intake in week two was significantly associated with a decrease in infant milk intake in week three, controlling for percent of ideal weight (R=0.613, P=0.028).

Other Findings

Significantly higher GWG in Experimental group; reported mean kcal intake in Experimental group below RDA and decreased significantly (approximately 32%) during week two (restriction week). Mean intake in Control group was lower than Experimental group during baseline and remained constant during week two. 

Subjects in both groups lost weight gradually during baseline; the Experimental group showed significantly greater weight loss during week to than during week one or three; there was no significant change in Control group in the rate of weight loss during the study. 

No significant differences in mean breast milk concentrations of prolactin, fat, lactose, gross energy between weeks for either group, nor between groups.

Author Conclusion:

Energy intake recommendations during lactation are higher than necessary and lower intake are compatible with successful lactation and gradual maternal weight loss. A gradual weight loss of 0.5kg per week during lactation is unlikely to be associated with any adverse effect on breast milk output. 

Funding Source:
University/Hospital: University of California-Davis
Reviewer Comments:

Small sample size; subjects self-selected group assignment; short duration; baseline food intake self-reported and not well-measured; physical activity not accounted for at any point during study. 

Compliance to the energy restriction diet was not measured.

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? 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? No
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) No
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? No
  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? 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? N/A
  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? ???
  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? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? No
  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? No
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? No
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? ???
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? No
  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? ???
  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? ???
  7.6. Were other factors accounted for (measured) that could affect outcomes? No
  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? No
  8.1. Were statistical analyses adequately described and the results reported appropriately? No
  8.2. Were correct statistical tests used and assumptions of test not violated? No
  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)? No
  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