STATS ARTICLES 2011
Can breastfeeding halt obesity - or is the media misreading the research?
Rebecca Goldin Ph.D, January 21, 2011
A recent study found that 32 percent of babies are obese. What are they eating?
The Surgeon General has issued a call to action on breastfeeding, saying that society should do more to encourage women to breastfeed their children. The call to action is eminently supportable, but as with many well-intentioned public health interventions - the temptation to stray beyond what the scientific data says, is great. But you don't multiply the effects of good policy simply by adducing false benefits. This is particularly the case with the increasingly widespread belief that breastfeeding is a solution to the obesity crisis among children.
A recent article published in American Journal of Health Promotion observes that 32 percent of babies are overweight at only nine months of age, a disaster of epidemic proportions on the face of it. But the study led MSNBC and AOL Health, among other media sources, to jump to a host of poorly reasoned conclusions that do little to address the problems behind a weight epidemic that has reached the youngest of us.
The study authors noted that the principal reason behind the fact that babies are packing the pounds is quite simply that they are eating bad food. The study cites French fries and sugared drinks – even soda in a bottle – as impacting the babies’ weight. Other weight-inducing activities include adding cereal to milk and introducing solid foods too early.
What did the press conclude? Mothers should breastfeed rather than use formula.
This study did not actually look at breastfeeding at all. Indeed, there is little evidence that using formula causes obesity. There is a correlation between formula use and obesity among babies and children (noted in several articles cited by the American Academy of Pediatrics), though this correlation is not consistent in all studies. Some of these studies show a relationship in only some demographics and not others. Others show that show that the disadvantage of bottle-feeding and/or formula mostly goes away by the time a child is about four years old.
However, none of these studies actually control for food consumption. The result is that we cannot discover whether breastfeeding is correlated with obesity because infant formula or bottle feeding leads to subsequent overeating or disposition to being overweight, or whether those parents who breastfeed are also more likely to offer their children green beans instead of French fries. Despite weak evidence, there is a lingering conviction that formula causes obesity among pediatricians and the press; if anything, the study about infants should make us reflect more carefully on this conclusion.
The simple observation by the study’s author that overweight kids are fed a variety of foods that are known to increase weight raises what should be an obvious question: are people who use infant formula more likely to eat at McDonald’s? If so, one cannot say that formula is the culprit for obesity rather than McDonald’s. The only way to do this is if these studies control for parental eating habits – and the problem is they do not. Typical controls include socio-economic status, education level, smoking status, and race. Fast food is not part of the equation.
There are other issues with labeling kids obese at this age. The definition of obese is that these kids’ lie in the top 5 percent of weight in growth charts published by the Centers for Disease Control. One might wonder how 32 percent can be found in the top 5 percent; the growth charts reflect the population in the 1960s. Undoubtedly, then, kids are bigger than they were 40 years ago. What we do not know is whether this is the correct number to label “obese”. In the 1960s, would one have said that a baby in the top 5 percent is obese, or simply a good eater? In other words, does being in the top 5 percent indicate an actual health problem?
Furthermore, being in the top 5 percent at age 9 months is only weakly predictive of being in the top 5 percent of weight at age 2 years. By then, more than half of those “obese” babies are no longer considered obese.
There is no indication from the study that this attrition of obesity among the fattest babies is due to intervention by parents and health care workers. If babies in the top five percent are already thinning by age 2, then the “obesity” diagnosis at age 9 months may be misplaced. At the very least, it has an impressively high false positive rate.
So why does the press continue to hound families about using formula? Babies gaining too much weight need us to focus on the real issues: large quantities of calories with poor nutritional value come from soda and junk food. Not from infant formula. At least CBS noted that the relationship was a “theory”.
An important note is that a good percentage of normal-weight children are reclassified as obese at 2 years old – pointing to the importance of good nutrition in children’s early years. The older the kids are when they are observed to be overweight or obese, the harder it is for them to lose the weight and get on a healthier lifestyle. Given that formula is recommended for use only until age 1 years old, it seems other foods given to toddlers are the culprit. Fries anyone?