Babies’ Eating Habits and Childhood Obesity

Sarah Pedersen

When are babies ready to eat solid food?  The American Academy of Pediatrics (AAP) tells us that most babies are ready at 4 to 6 months of age. You’ll know if your baby is ready to eat solid food if he or she can sit upright and hold up his or her head; is curious, looking at everything around him or her; watches you feed yourself; has mastered tongue movement; and seems hungry after getting a full day’s portion of milk (8 to 10 breastfeedings or about 32 ounces of formula). AAP recommends waiting until the baby is at least 4 months old because introducing food earlier can increase the chances of childhood obesity.

A study by researchers at Harvard University, which followed 847 children from birth to the age of 3, looked at the link between when solid food was first given to babies and obesity in preschool-age children. The study drew several important conclusions on the importance of breastfeeding and the effects of introducing solid food to babies on formula too early or too late.

Among babies who had been breastfed for 4 or more months, the timing of the introduction of solid food was not linked to obesity at age 3. In other words, breastfed babies who began eating solid foods outside of the recommended window (before 4 months of age or after 6 months) were not likely to be obese once they reached pre-school age.

This was not true for formula-fed babies, who were much more sensitive to when they first began eating solid food.

  • Babies who were introduced to solid food before 4 months of age and who were never breastfed or were breastfed for less than 4 months were 6 times more likely to be obese by age 3 compared to formula-fed babies who had been introduced to solid food between 4-5 months.
  • Formula-fed babies who had not been introduced to solid food until after 6 months of age were almost 4 times more likely to be obese than those who had started eating solid food between 4-5 months.
  • Babies who started on solid foods before 4 months of age were much more likely to be formula-fed, with 33% of “early eaters” being formula-fed compared to only 8% of breastfed babies. “Late eaters”—babies starting on solids after 6 months—however, were much more likely to be breastfed: 17% of breastfed babies compared to 9% of formula-fed babies.

It’s not clear why the timing of solid food is so important for formula-fed babies, and it is especially surprising that formula-fed babies who begin eating solids late are at almost as high a risk for being obese at 3 years of age as formula-fed babies who start on solids too early. It may be that mothers who use formula are somewhat less tuned in to their baby’s hunger cues and feed them too much (perhaps encouraging them to finish the bottle) or too often. Another reason may be that formula-fed babies significantly increase their calorie intake when solids are introduced. While breast milk changes as a baby grows, formula does not change. As a result, formula-fed babies may be eating too many calories, while breastfeeding may help babies and mothers manage the amount and type of calories consumed. Although formula producers have introduced staged formulas, they have yet to introduce a formula for children 4 to 6 months—the optimal window for introducing solid food—which would contain fewer calories. That would allow mothers to better control what and how much their baby eats.


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