Childhood overweight affects approximately 17 percent of U.S. children and is increasing. Effective interventions performed at critical time points are likely crucial to the prevention of overweight. The first few months of life may present such a critical time point. Infant feeding practices are thought to be a major contributor to early rapid weight gain, and this gain may increase risk of childhood overweight. Significant differences have been well-established between exclusively breastfed and formula-fed infants in terms of growth and intake during the first year of life, with formula-fed infants taking in more energy and growing at a faster rate than breastfed infants. Formula-fed infants are more likely to be overfed than breastfed infants and may be less able to self-regulate energy intake than breastfed infants.
Although factors driving these differences are likely to include biological factors present in breast milk and absent in formula, behaviors inherent to bottle feeding also influence these differences. One such behavior is infant formula preparation. Properly reconstituted powdered formula should provide 20 kilocalories (kcal) per ounce. Twenty-two kcal per ounce is used to produce “catch-up” growth in preterm infants and, therefore, small differences in reconstitution can have a biologically meaningful impact. Previous work has indicated that, in spot samples collected from mothers in a Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) population, more than two-thirds were overdiluted (<18 kcal/ounce). Should infants habitually receive overdiluted infant formula, they could conceivably increase hunger cues and mothers could interpret these cues as readiness for other foods or fluids. Early introduction of solid food is a risk factor for later childhood overweight. Conversely, an infant habitually exposed to a high-energy infant formula would be expected to gain weight if unable to self-regulate intake. Developing methodology to identify mothers at risk for these behaviors, and subsequently intervening, may have an impact on long-term child weight outcomes.
Nearly half of the infants in the United States are served by the WIC program, which has recently reduced the amount of formula in some versions of the WIC food package. Although the intention of these changes is to equalize the value of the formula feeding and the breastfeeding food packages, the unintentional result may be an increase in overdilution of powdered or from-concentrate formula as caregivers anticipate a decreasing supply. This policy change, paired with the current national economic crisis and recent media reports of “watering down” infant formula, makes this project especially timely. The formula samples collected for this project were collected prior to implementation of the changes in the WIC food package and therefore establish baseline data, which will be useful in detecting any future change.
The study was a cross-sectional, observational design with two groups of formula-feeding mothers: an income-eligible WIC-participant group and a non-WIC-income-eligible group (income > 185 percent of Federal poverty level). Mothers of healthy, term, formula-fed infants up to 6 months of age were recruited from the WIC program and from a university-housed birth registry. Via telephone survey, mothers responded to a series of questions about formula preparation and infant feeding. Mothers who qualified for this larger study and who also (1) had infants up to 4 months of age and (2) were exclusively offering reconstituted powdered infant formula (no current breastfeeding or other foods or fluids) were invited to participate in a sub-study. This subset of mothers recorded infant intake for 24 hours and collected a 15-milliliter sample of infant formula from each bottle offered prior to offering the bottle to the infant. Upon collection of the samples, these mothers were asked the same series of questions and their infants were weighed and measured. Samples were stored at -20° centigrade until analyzed using the loss-on-drying method.
The average age of the 40 mothers completing the telephone interview was 30.5 years, with infants averaging 4.1 months. Eighteen mothers were WIC-income-eligible, and the remaining 22 were above this income cutoff. Twenty one of the infants were male, and 19 were female. Mothers were read several statements regarding formula preparation and asked to respond in the following manner: Disagree (1), Slightly Disagree (2), Neutral (3), Slightly Agree (4), and Agree (5). There were no differences by income level to the statements (see table). However, there was a trend in differences between infant sex and disagreement with the statement regarding “over-strong” formula, with mothers of males tending to disagree more strongly (p=0.09). Maternal age appeared to be a potential factor in formula-preparation opinions, with older mothers tending to disagree more with the statement regarding thin formula being okay (r=-0.532: p=0.0768).
Responses by formula-feeding mothers to statements regarding formula preparation (n=40):
I think it is important to be very careful when mixing up formula mean = 4.8 (0.65), range = 2-5
I think formula that is a little over-strong is okay for my baby mean = 1.2 (0.70), range = 1-4
I think formula that is a little thin is okay for my baby mean = 1.5 (1.15), range = 1-5
I think parents learn how much formula should be added to water and don’t have to measure exactly mean = 1.5 (1.18), range = 1-5
Eighteen mothers provided a 24-hour sample of prepared formula for their infants (average age of 3.1 months). “Normal” energy density was defined as 18-22 kcal/ounce. Results indicate that, although the average kcal/ounce was 18.5, 26 percent of the mothers were consistently overdiluting the infant formula (<18 kcal/ounce); the overall average range was 14.5-23.0 kcal/ounce. There were no differences by income level. In addition, results of the questions regarding infant formula preparation indicate that behaviors may be both intentional and unintentional. Although the sample size was small, overdilution appears to be a potential issue in this formula-feeding population, regardless of income level. Further research could include investigating these behaviors and their potential impact on infant anthropometry.
Direct inquiries about this study to the Project Contact listed above.