EAL

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

Citation:

Barbosa L, Butte NF, Villalpando S, Wong WW, Smith EO. Maternal energy balance and lactation performance of Mesoamerindians as a function of body mass index. Am J Clin Nutr. 1997; 66: 575-583.

PubMed ID: 9280176

Study Design:

Logitudinal cohort study

Class:

B - Click here for explanation of classification scheme.

Quality Rating:

POSITIVE: See Quality Criteria Checklist below.

Research Purpose:

To investigate the relations between maternal energy balance, lactation performance and infant growth, with the expectation that maternal energy balance would be a key determinant of lactation performance in women with lower body fat.

It was hypothesized that negative energy balance in conjunction with lower body energy reserves will adversely affect daily fat secretion and concentration of breast milk, and consequently the growth of exclusively breast-fed infants.

Inclusion Criteria:

Lower BMI (<23) and higher BMI (≥23)
Age 18 years to 35 years
Parity fewer than five
Free of chronic diseases
Not taking any medications or consuming alcohol.

Exclusion Criteria:

Not reported.

Description of Study Protocol:

Recruitment

Women recruited from local prenatal clinic in the community.

Design

Longitudinal observation study.

Statistical Analysis

Chi-square and unpaired T-tests to test for differences in maternal and infant characteristics between groups; Pearson correlation coefficients and linear regression to test relations between physiologic variables; ANOVA with repeated measures to test differences between three months and six months postpartum; P≤0.05.

Data Collection Summary:

Timing of Measurements

0.5 months, three months and six months postpartum
- Lactation performance (milk production, composition, infant growth)
- Maternal body weight and composition
- Infant growth
- Maternal energy balance.
Three months and six months postpartum
- Dietary intake
- Milk production
- Milk composition.

Dependent Variables

Lactation performance (milk production, composition, infant growth)
Maternal body weight and composition
Infant growth
Maternal energy balance, calculated at 0.5 months to three months, three months to six months and 0.5 months to six months via 1) changes in body weight converted to energetic equivalents by using 27.2Mj per kg; and by 2) changes in fat-free mass (FFM) and fat mass (FM) converted to energetic equivalents by using 4.6Mj per kg and 39.3Mj per kg, respectively
Dietary intake.

Independent Variables

BMI group (BMI<23 or ≥23).

Control Variables

Timing of measurements throughout study.

Description of Actual Data Sample:

Initial N: N=40 (21 in BMI<23; 19 in BMI≥23)

Attrition (final N): N=38 by six months

BMI<23 group (N=20): BMI 21.4±0.9, range 18.5-22.8; age 21.3 years±4.3 years; gravidity 2.9±1.4; parity 2.7±1.3

BMI≥23 group (N=18): BMI 25.7±1.9, range 23.1-29.1; age 22.4 years±3.0 years; gravidity 3.0±1.6; parity 2.7±1.6

Ethnicity: Otomi Indian

Location: San Mateo Capulhuac, Sierra Madre del Sur, Mexico.

Summary of Results:

Variables	BMI <23 (N=20)	BMI ≥23 (N=18)	Statistical Significance of Group Difference
Weight change (kg), from 0.5 months to six months	-1.25±1.94	-0.34±2.5
Body fat change (kg), 0.5 to six months	-1.4±2.77	0.82±3.55
Milk production (g/d), six months	823±222	752±148	ns
Feedings per day, six months	12.9±2.0	12.6±2.6	ns
Milk energy (kj/g), six months	2.53±0.33	2.80±0.46	P=0.01 from three months to six months
Milk fat (mg/g), six months	29.1±8.7	35.7±9.2	P=0.04 BMI group
Daily milk energy (kj/d), six months	2,061±502	2,058±363	P=0.01 from three months to six months
Daily milk fat (g/d), six months	23.4±7.7	25.7±5.3	P=0.02 from three months to six months

In both groups, weight decreased over six months (P=0.04); in BMI<23 group, body fat decreased significantly (P=0.04), and milk fat concentration was positively correlated with body fat at three and six months (r=0.32 and 0.40, P=0.04 and 0.01, respectively).

Energy balance not associated with milk production or composition, milk nutrient composition, or infant growth, except at six months when energy balance was positively correlated with milk energy and fat in BMI<23 group (r=0.55, P=0.01).

Author Conclusion:

Negative energy balance in conjunction with lower energy reserves did not adversely affect lactation performance or infant growth in this population of Otomi Indians.

Funding Source:

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?		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?	Yes
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?	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.)	Yes
	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?	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?	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)?	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?	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