by Mary Jessica Hammes
July 05, 2010

We know that breastfeeding reduces the risk of childhood obesity, but how? A new study published in the journal Pediatrics found that it may have to do with babies inability to self-regulate their milk intake—whether that’s expressed breast milk or formula—when they drink from bottles.

Around 17 percent of children and adolescents ages 2-19 are obese, according to the Centers for Disease Control and Prevention (CDC). For children 2-5 years old, obesity increased from 5 to 10.4 percent between 1976-1980 and 2007-2008; for children 6-11 years old, the obesity rate increased from 6.5-19.6 percent; and for 12-19-year-olds, it increased from 5 to 18.1 percent.

Obese children are more likely to become obese adults, putting them at risk for high cholesterol levels, high blood pressure, abnormal blood sugar levels, asthma, hepatic steatosis (liver damage due to high levels of liver enzymes), sleep apnea, and Type 2 diabetes.

That breastfeeding reduces the risk for childhood obesity is old news. Breastfeeding has long been linked with a reduced risk of obesity, based on research from 2004, 2006, and 2007. But this new study is the first to look at infant’s self-regulation of food intake as the possible mechanism.

Research
The question posed by the study authors—“Do Infants Fed From Bottles Lack Self-Regulation of Milk Intake Compared With Directly Breastfed Infants?” demands just one answer, and, according to the study results, that answer is yes.

Researchers Ruowei Li, Sara B. Fein, and Laurence M. Grummer-Strawn analyzed data from the 2005-2007 Infant Practices Study II, a large-scale study conducted by the Food and Drug Administration and the CDC. Participants received monthly questionnaires, and researchers were able to look at complete data for 1,250 infants.

Results
Data showed that babies who were bottle-fed in early infancy were more likely to empty their bottles or cups in late infancy, regardless of the type of milk in the bottle or cup. The numbers are substantial:

• 27 percent of babies who were exclusively breastfed in early infancy emptied their bottles in late infancy
• 54 percent of babies who were both breast- and bottle-fed emptied their bottles in late infancy
• 68 percent of exclusively bottle-fed babies emptied their bottles in late infancy

“Bottle-feeding, regardless of type of milk in the bottle, is distinct from feeding at the breast in its effect on infants’ self-regulation of milk intake,” the study’s authors wrote.

So, do babies who keep drinking until the bottle is dry—regardless of whether they are actually still hungry—repeat this behavior with food and drink as kids? Well, no one can say for sure; in fact, that is one of the study’s self-proclaimed limitations (along with underrepresenting black and Hispanic mothers, and the possibility that reporting errors may have occurred.)

It would make sense that eating patterns established in infancy would affect later childhood. But there is more at work here.

The study authors suggest three main reasons to explain the disparity in self-regulation:

1. Breastfeeding babies control intake since they decide when to start and stop suckling; bottle-fed babies are less likely to control milk intake. When babies are encouraged to finish a bottle completely despite being full, they don’t learn to regulate their intake.
2. Breastfeeding requires both non-nutritive and nutritive sucking. The baby’s sucking triggers the let-down reflex, so there are moments in which the baby is sucking but not actually getting any milk. This very transition in sucking styles may affect self-regulation: when babies control the milk flow by adjusting their sucking, “they may establish a greater level of responsiveness to internal cues of hunger and satiety,” according to the study. This way of sucking does not exist in bottle-feeding.
3. Breast milk varies in composition and taste. Near the end of a feeding, the fat content in the breast milk is higher, which may signal to the baby that the nursing session is coming to an end. This signaling doesn’t happen with bottle-feeding. The study’s authors also suggest that missing out on the “sensory experience” of varied breast milk flavors may effect the regulation of food intake later in life.

Recommendations
All children, regardless of how they were fed as infants, can maintain a healthy weight throughout their lives—with their parents’ guidance.

If you bottle-feed your baby, remember that newborns may take only an ounce or two of formula at each feeding; by two months, it may be just 3-4 ounces. Watch for hunger cues (your baby may smack his lips or put his hands to his mouth) and check for his rooting reflex (turning his head toward your hand when you touch his cheek). And remember that crying is actually a late indicator for hunger, so don’t wait for your baby to cry to feed him.

When your child is older, continue to encourage healthy eating habits and regular physical activity; you can find inspiration in the CDC’s tips on preventing childhood obesity. If you struggle with weight, become an example for your child and strive to stay healthy together. Take a look at the newest version of the food pyramid and be an active participant in your child’s life.

The best advice for new moms is to breastfeed your baby for at least a year (exclusively for the first six months). However, any amount of breastfeeding for any length of time benefits your child—and you.