One of the key factors associated with child obesity is a rapid rate of
weight gain during infancy. Infant feeding practices are a major contributor
to early rapid weight gain. Formula-fed infants consume more energy
and gain weight more rapidly than breastfed infants, even during the first
few months of life. Recent evidence indicates the effect of infant feeding on
body fatness is long term, with children and adolescents who were breastfed
being 20-30 percent less likely to be overweight than children who were
formula fed. The mechanisms underlying these differences are not well
understood. One possibility is that the composition of infant formulas has a
stimulatory effect on intake and growth, although recent data from one of
our own studies suggest that neither the protein content or quality, nor the
potential renal solute load of formula, is the trigger. Another possibility is
that bottle-feeding, not the composition of the milk in the bottle, is more
important. One hypothesis is that infants are born with the ability to self regulate
their energy intake. The bottle-feeding caregiver may miss the
infant’s satiety cues or encourage the infant to empty the bottle.
The objective of this study was to evaluate whether formula-feeding caregivers
who are encouraged to be more sensitive to their infants’ satiety cues
and to adopt feeding practices similar to those of breastfeeding mothers will
in fact alter their feeding practices. The study further examined if this action
results in a lower volume of formula consumed at 4 months of age and less
rapid weight gain from 1-4 months of age.
This project was a double-blind, randomized educational intervention
trial with exclusively formula-feeding caregivers in the Special Supplemental
Nutrition Program for Women, Infants, and Children (WIC) in
Sacramento County. Some of the ideas for this intervention were the result
of focus groups conducted with WIC mothers in spring 2003, which
revealed that overfeeding formula-fed infants is common in this population.
The intervention group received education that promoted awareness of early
satiety cues and discouraged the use of large bottles (greater than 6 ounces)
before 4 months of age. The control group received standard nutrition
education regarding introduction and feeding of solid foods. After initial
screening, caregivers completed a baseline 2-day formula intake record and
were then randomized to attend either the intervention or control nutrition
education class. Subjects were stratified by infant sex and maternal language
(English or Spanish) and were randomized using computer-generated stratified
random lists with a block size of four. All subjects who attended the
class were then followed for no less than 2 months post-class. Formula
intake records were again completed at 2 weeks post-class and at approximately
3.5 months of age. At baseline and at about 4 months of age, infant
anthropometry was completed. To identify underdilution or over-dilution of
formula, caregivers were asked to provide samples of prepared formula at
baseline and at the end of the study.
Of the 836 caregivers screened at the 2 clinic sites, 214 were eligible and
104 were willing to participate in the study. The most common reason for
refusal was lack of time. Barriers to participation included lack of transportation
to the nutrition education class, uncertainty about ability to attend
the class, and family or personal problems. Of the 104 women who agreed
to participate, 101 completed the baseline questionnaire and 61 completed
the first formula intake record. The remainder (n=43) did not complete the
baseline intake record and therefore were not included in the randomized
trial. In most of these cases, the research staff was never able to reconnect
with the caregivers, even after multiple attempts.
Of the 61 caregivers who completed the first intake record and were randomized,
17 never attended the nutrition education class (16 had been scheduled
for the class but did not show up even after repeated rescheduling). Of the
44 caregivers attending the nutrition education class, 40 caregivers
completed the final formula intake record and 38 of these attended the final
measurement session. Among the 40 caregivers who completed the final
intake record, no significant differences emerged between intervention and
control groups in maternal age, education, body mass index, number of children
or ethnicity, or infant birth weight, sex, or formula intake at baseline.
Differences between groups were not significant in formula intake at the
second record or at the end of the study, even after controlling for infant age
at baseline, baseline intake, sex, birth weight, and time in the study. No
significant differences emerged between groups in bottle-feeding behaviors
at baseline or at the final intake record, including the mean percentage of
bottles emptied, the percentage of subjects who emptied the bottle at more
than 50 percent of feedings, and the percentage of bottles offered that were
greater than 6 ounces. Bottle-emptying increased in both groups over time
(from 50-60 percent of feedings), as did the use of bottles greater than 6
ounces (from less than 5 percent to about 17 percent of subjects).
Differences were not significant between groups in infant weight, length, or
sum of skinfold thickness at baseline, after controlling for age and sex.
However, by the end of the study, infants in the intervention group were
heavier and longer than those in the control group, even after controlling for
age at measurement, sex, baseline weight or length, and time in study. In addition,
the sum of skinfold thickness was greater among infants in the intervention
group than in the control group after controlling for age at measurement
one, time in study, sex, and sum of skinfold thickness at baseline.
Response to the nutrition education class, followup phone call, and the key
messages was overwhelmingly positive. Most caregivers in the intervention
group could accurately repeat the key messages and the demonstrations used
to transmit them and felt that they were easy to comply with and to share
with friends and family. However, this response did not appear to translate
into behavioral change.
The adult learning technique used for this intervention was designed for use
in a group setting, but 95 percent of the classes were conducted with just
one caregiver because of no-shows. Although the caregivers seemed to
appreciate the one-on-one nature of the classes, the lack of group facilitation
may be one reason for not achieving changes in feeding practices. Other
possibilities include (1) inadequate reinforcement of messages, (2) insufficient
depiction of and/or practice with identifying satiety cues in human
infants, (3) not intervening early enough in the feeding relationship to
support and foster inherent infant self-regulation, (4) not following caregivers
long enough to detect a potential change in bottle-feeding behaviors,
and (5) other barriers to responsive feeding related to the desire for infants
to cry infrequently and sleep more.
In summary, the results of this study indicate that formula intake by infants
in this population are quite high—probably reflective of overfeeding—and
that modifying bottle-feeding behaviors to prevent overfeeding is a challenging
task. The more rapid growth of infants in the intervention group is
difficult to explain, given that differences were not significant in the intake
variables. The final sample size was quite small, and caregivers participating
in the project were not representative of the WIC population in
general, which limits the conclusions that can be drawn. However, even
though caregivers did not report a difference in intake or bottle-feeding
behaviors, the educational intervention was successful in improving knowledge
and awareness of the key messages.