Researchers from the University of Iowa found that babies fed lactose-free or hydrolyzed formulas gained weight faster in their first year, raising new questions about how modern formula compositions may shape lifelong health.
Study: Effects of Infant Formula Type on Early Childhood Growth Outcomes: A Retrospective Cohort Study. Image credit: New Africa/Shutterstock.com
With childhood obesity rates hitting 20% in the United States, American scientists are looking at its origin in infancy and before birth. A new study in Nutrients explores the effects of non-standard infant formulas on early childhood growth.
Introduction
What the baby eats during the first three years of life shapes its metabolism. This is traceable to its gut microbiome development and the direction in which its metabolic pathways move in response to its feeding. These early nutritional factors help shape long-term health outcomes.
Breast milk is recommended for infant food until six months of age. However, less than a quarter of American infants (23%) are exclusively breastfed for this duration. While the American Academy of Pediatrics (AAP) and American Dietary Guidelines recommend that non-breastfed babies receive iron-fortified formula, no other specific guidelines have emerged. The US Food and Drug Administration (FDA) specifies that formula must contain minimum levels of 30 essential nutrients. Still, it does not specify the type and amounts of macronutrients (proteins, sugars, and fats) in the formula.
Most powdered infant formula sold today in big American retail outlets is non-standard infant formula. About 60% of it is lactose-free or lactose-reduced. The lactose is replaced with other sugars like maltodextrin (a glucose polymer) or sucrose (table sugar). This is surprising because of the relative rarity of lactose intolerance and is concerning because lactose promotes good gut bacteria like Bifidobacteria. These bacteria form metabolically essential, immunity-promoting short-chain fatty acids like butyric and propionic acid.
Previous research suggests that the rapid breakdown of sugars in non-standard formula to glucose may increase the blood sugar levels, reduce feelings of fullness, and habituate the baby to prefer sweet-tasting food. Such changes could also shift the gut microbiome and affect later metabolic regulation.
The protein in infant formula is often hydrolyzed for easier absorption. Hydrolyzed protein may also be absorbed faster than ordinary milk protein, potentially leading to faster weight gain. However, the study did not measure appetite or obesity outcomes, so these mechanisms remain speculative.
Despite the widespread availability and use of non-standard infant formula, little evidence exists showing how it affects the infant’s growth and metabolism. The current study seeks to provide some evidence by comparing non-standard and standard formula use in full-term babies.
About the study
This was a retrospective cohort study, where the investigators used data on full-term babies who weighed more than 2,500 g at birth. Mothers were asked about the type of infant formula used, whether standard or non-standard, and whether the child was breastfed, at the two-month well-baby visits.
Growth was assessed using continuous growth scores at one and two years of age. The babies were not classified as obese or overweight because, at such young ages, there are no appropriate criteria for these conditions. The analysis of the feeding-growth relationship was adjusted for the mother’s socioeconomic characteristics.
The study included 5,515 babies. At two months, about a third (35%) received only breast milk. Of the rest, 42% and 23% received standard vs. non-standard infant formula.
Study findings
Breastfeeding mothers were more likely to be White, privately insured, and less likely to have obesity or anemia. At one year, their babies were more likely to be still receiving breast milk compared to cow’s milk or formula in the formula-fed group.
At 12 months, babies fed non-standard formula had higher growth rates than those fed standard formula. This was true for weight for age and body mass index (BMI). While the weight for length also appeared to be higher in the non-standard formula group, the difference disappeared after adjusting for other factors.
The study found that, based on subgroup analysis, female infants on non-standard formula showed a greater increase in BMI z-scores at 12 months compared with males. Infants with Medicaid or private insurance had higher BMIs with the non-standard formula at 12 months. Differences varied by subgroup, with non-Hispanic and White infants showing somewhat higher BMI z-scores at 12 months with the non-standard formula.
At 24 months, non-standard formula-fed babies remained heavier for their age than standard formula-fed babies. Both groups of formula-fed babies had a higher growth trajectory than breastfed babies at 12 and 24 months.
Implications
As expected, babies on non-standard formula showed a significantly higher BMI than those on standard formula or breast milk. The authors note that this pattern of accelerated early growth could increase the risk of later metabolic problems, though this study did not directly assess obesity or metabolic outcomes.
However, the study collected feeding information only at the two-month visit, creating an important gap in understanding how feeding practices may have changed over time. Long-term follow-up research is needed to fill this gap. Again, given that the current FDA requirement is that approved formulas should support adequate infant growth for 15 weeks, such research is needed to support the long-term safety of non-standard formulas.
Conclusions
Infant formula affects infant growth differently from exclusive breastfeeding. Non-standard infant formula appears to increase early growth rates, particularly in the first year of life, compared to standard formula. Further work is important to understand how non-standard formula affects the risk of obesity and the long-term health outcomes in users.
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